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Equipment Discussions >> Cats & Casses

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Eddgie
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Reged: 02/01/06

Why do people even buy SCTs???
      #6223155 - 11/29/13 10:55 AM

Nothing is right about them.

None of the manufacturers flock the inside of the baffles, and gee, if the manufacturers only did this, it would improve the contrast by 50%.

And the obstruction is huge. If they left off the secondary baffle, they could reduce the obstruction by 4%.

And they don't come in a Truss design.

And the corrector is not in the right spot. By making the tube 30% longer and moving the corrector, they could make it better.

And seeing makes them useless for planetary observing. You can't even get the moon into focus it affects SCTs so bad.

Oh, and cooling. You can't even see stars I guess unless you put in cryogenic refrigeration plumbing. I mean why bother using them at over 75x when you can use a refractor at 75X and see the same size true field. Sure, nebula and extended targets will be brighter, but they are wiggling around so much and they are sooo blurry that what it the point????

I just don't get it. How can so many people be so happy with what is more of a kit car than a telescope it would appear. The thing is practicallly unusable out of the box. You have to take it apart and competely rebuild it to make it work as well as a 100mm APO.

I will never buy another one. I just don't have the time to rebuild it in order to get it to be even marginally useful.

Just kidding of course. I get the "ATM" spirit.

But all of these "Mod" posts really make me wonder sometimes if the commercial SCT is worth the time and effort if so many mods need to be made to get it to perform well?


I have just been so thrilled with my SCTs in the past. Most of them were really able telescopes that presented me with hundereds of hours of wonderful observing. And none of the mods I tried seemed to make any meaningful difference for my own observing needs that I stopped chasing the "Mod of the day" a long time ago. And the bigger I went, the more I enjoyed them. The more I could see. More deep sky, more planetary detail, more stars in clusters. No mods or anything. I just went bigger and bigger and saw more and more.


The SCT is not the scope people love to hate, it is the scope people hate to love.... It seems like so few people "Believe" in their SCTs.

These forums make it hard for me to continue recommending SCTs to people though. I used to make the C8 my "Standard" recommendation for people wanting their first telscopes. Enough apeture to do great all around observing. Inexpensive, easy to store and transport, comfortable to use, and just a great telecope.

But these days, I am more inclined to recommend a small refractor. Nothing to do. Just plug and play.

That is the world we live in.

I am starting to get the refractor forum's superiority complex.

Modders, please do not take offense. This is not directed at any individual. Rather it is just a rant about how so many people perceive so much wrong with a design that I have loved dearly over the decades, but now feel as if may be damaged by the perception that there is so much wrong with them.. So sad. Great telescopes.

At least one person loves them just the way they are...

Edited by Eddgie (11/29/13 11:08 AM)


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223190 - 11/29/13 11:17 AM

I love my SCT's, especially my C6! I have a large refractor
but hardly use it because of the pain in my back it gives me!
Newtonian, have that too, quite sharp, but I live in IOWA the windiest part of the Nation,dont believe me? just ask the 20,000 Migrating birds that run into all the Wind turbine
generators each year!
So I'll keep my stubby, Ugly, Blurry Worthless sct


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Martin Lyons
sage
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Reged: 10/06/08

Loc: Cape Town, South Africa
Re: Why do people even buy SCTs??? new [Re: orion61]
      #6223196 - 11/29/13 11:20 AM

Yep, SCTs suck........

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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223198 - 11/29/13 11:21 AM

They are great scopes. But, what's wrong with someone doing a lot of work. If they want to and the scope can be made even better...

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drago
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Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223205 - 11/29/13 11:23 AM

very good question.
all these may be formed to one: why people do dumb things?
What you think, why?
i think, in general, because most of people is that, about what Einstein says "Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe."

Edited by kkokkolis (11/29/13 03:55 PM)


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Roy McCoy
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Reged: 10/13/05

Loc: Glendale, AZ
Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223225 - 11/29/13 11:33 AM

You had me up until the word "thrilled".


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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Why do people even buy SCTs??? new [Re: Roy McCoy]
      #6223296 - 11/29/13 12:17 PM

SCT's have one fatal flaw. They cannot hold their own against telescopes 10x their price.

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herrointment
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Reged: 03/12/11

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Re: Why do people even buy SCTs??? new [Re: Roy McCoy]
      #6223299 - 11/29/13 12:20 PM

What the dog said.

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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: Footbag]
      #6223300 - 11/29/13 12:20 PM

Quote:

SCT's have one fatal flaw. They cannot hold their own against telescopes 10x their price.




they cannot hold even against cheaper newtonians. newtonians have smaller central obstruction, less light loss and scatter taht catadioptrics. imho only cat's pluss in general is their compact size. all another compared to newtonians and refractors, is minuses...


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Joe Aguiar
Carpal Tunnel
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Reged: 02/10/07

Loc: none of your buss
Re: Why do people even buy SCTs??? new [Re: Footbag]
      #6223307 - 11/29/13 12:23 PM

eddie your funny

i love scts they are called the best all round general telescope, not the best in a specific field, but i think it does give decent views on most stuff.

Its the size that makes it one of the best selling kinda scopes.

I cant imagine using a 12" F/10 refelctor ( i dont even think they make one)normally in this size its an F/4.8 to 5.

At about 2ft long no other scope in its size class can match the portabililty, and iam sticking to this LOL


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rmollise
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Reged: 07/06/07

Re: Why do people even buy SCTs??? new [Re: drago]
      #6223347 - 11/29/13 12:41 PM

Quote:



they cannot hold even against cheaper newtonians. newtonians have smaller central obstruction, less light loss and scatter taht catadioptrics. imho only cat's pluss in general is their compact size. all another compared to newtonians and refractors, is minuses...




Newtonians are fine if you just want to look. If you decide you want to do more than that, the SCT is far more versatile and adaptable.


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DesertRat
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Reged: 06/18/06

Loc: Valley of the Sun
Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6223362 - 11/29/13 12:55 PM

Maybe some have too many cloudy nights? Some just like to do ATM like stuff. Amateur astronomy has all kinds of people, and lets hope that's always the case.

Some just like to come to Cat&Casses and leave newt (or other) bombs. Clearly too much time or too many cloudy nights or maybe they just got lost?

By the way, my first serious scope was a 8" newt. Very nice and great memories.

Love is not a word I associate with a telescope. I am strongly attached to my Edge14. The best scope in its class I've ever used. I like my refractors and Mak, but that SCT is special.

One thing though, in my climate the TEMP-est fan system has clearly improved cooldown. At least for me. If I lived somewhere were temps did not fall like they do here I would not even need that.

The C8 is an ideal starter scope. Celestron's sales record for them is a clear indication that many have had plenty of enjoyment from them.

Can we all just get along and enjoy the heavens and avoid or ?

Glenn


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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Why do people even buy SCTs??? new [Re: drago]
      #6223378 - 11/29/13 01:07 PM

Quote:

Quote:

SCT's have one fatal flaw. They cannot hold their own against telescopes 10x their price.




they cannot hold even against cheaper newtonians. newtonians have smaller central obstruction, less light loss and scatter taht catadioptrics. imho only cat's pluss in general is their compact size. all another compared to newtonians and refractors, is minuses...




That does kind of go back to my point about their price. With an SCT, you get a build quality that you don't get in the cheaper newts. I would say the build quality of SCT's is well beyond the starting price newts. And after the starting price points, Newts jump. Personally, I think AT needs to boost the build quality and introduce premium imaging newts.

It's also nice to not need a coma corrector.

But, most people seem to be comparing Edge to refractors. An Edge vs a Newt would be an interesting shootout.


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Steve Darden
professor emeritus


Reged: 07/29/07

Loc: GA
Re: Why do people even buy SCTs??? new [Re: Footbag]
      #6223390 - 11/29/13 01:17 PM

I hate my C8 so much that it may be the last telescope I buy.

Just kidding of course. I had a 10 inch dob and while it showed more than the C8, it wasn't comfortable for me to use. I also didn't like that the optics were open and got dirty quickly.

Both designs have their benefits and while I may buy a bigger dob some time in the future, the C8 is the scope I use when I have more than an hour to view.


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David PavlichAdministrator
Transmographied
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Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223404 - 11/29/13 01:26 PM

I've been an SC owner since I attended my first outreach. Our club president at the time had a C11 on a G11 set up next to me with my C6R on an Atlas. After looking at Jupiter for a while through my scope, I wandered over to Ron's C11 and at that point, I was hooked. It was a well turned C11 that was acclimated and collimated. Jupiter looked great! The only scope on the field that bettered it was a 16" NightSky dob.

It's a very versatile design that gives a lot of options for visual and imagers alike. You just have to know how to treat them to get the best out of them.

David


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BKBrown
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Reged: 08/23/09

Loc: Northern Virginia, USA
Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223478 - 11/29/13 01:56 PM

Portability of aperture, price point, versatility...all things I associate with SCTs. I am fortunate to have an excellent C9.25 XLT and an even better C11 Edge HD; how that happened I can't imagine since "the mass market quality control" on these scopes is clearly so bad Fact is, I haven't personally owned a real dog of an SCT so I don't understand what the complaints are about. And being a lunar and planetary imager, I am content to settle for the scope of choice used by many of the top amateur LP imagers in the field today...

Clear Skies,
Brian


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rcdk
super member


Reged: 11/13/10

Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223502 - 11/29/13 02:11 PM

Good post.

I used to hate them. Then I bought one. The only mod I made was Bob's knobs, but it is rarely necessary to touch them.

Which is odd considering the main reason I never liked them before is because I had literally never looked through one that was properly collimated. Finally a friend (who knows how to properly collimate a scope) bought a used Dynamax and I was blown away by the sharpness of the image.


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coinboy1
sage
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Reged: 05/03/11

Loc: Tulsa, OK
Re: Why do people even buy SCTs??? new [Re: BKBrown]
      #6223511 - 11/29/13 02:15 PM

I love my C11. Its the older carbon fiber Nexstar 11 GPS but it has excellent optics. I make optics as a hobby and have made a 9.25" 1/13 wave parabolic mirror and I can say that my C11 image quality is very good. Its compact size is amazing. I can haul my C11 around much easier than my 9.25" newtonian. My C11 also has the ability to accept Hyperstar. You know, for imaging at F/2. What other telescope can be at a Native F/2 and a Native F/10. I can use my SCT for high focal length planetary imaging (no diffraction spikes to deal with) or SUPER wide FLAT field and SUPER FAST F/2 imaging.

I believe the SCT has an excellent bang for the buck. The SCT has some of the larger after market accessories available to them. I am an amateur telescope maker and have made several newtonians but I still much prefer my SCT for viewing and imaging for these reasons.

Also collimation in an SCT is easier than a RC telescope. I have a 6" AT6RC and collimation is a HUGE pain the but. My C11 SCT holds collimation very well and produces excellent images. Plus my SCT central obstruction is considerably smaller than the Ritchey Chretien.

I dont understand the point of this thread. The SCT is an excellent scope for viewing and imaging. And if you dont like the heavy curvature of field for your SCT for imaging, get a good field flattener/focal reducer. There are plenty of them out there made JUST for them. Other telescopes dont have as many options IMHO.


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MikeML
professor emeritus
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Reged: 10/09/04

Loc: NJ
Re: Why do people even buy SCTs??? new [Re: coinboy1]
      #6223519 - 11/29/13 02:18 PM

Because I only have space for so many telescopes.

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jimbo728
sage


Reged: 11/05/13

Loc: Central NH
Re: Why do people even buy SCTs??? new [Re: MikeML]
      #6223558 - 11/29/13 02:40 PM

There is nothing wrong with an SCT that a bigger SCT wont cure.
Jim


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JohnH
Carpal Tunnel
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Reged: 10/04/05

Loc: Squamish BC Moved!!!!!
Re: Why do people even buy SCTs??? new [Re: MikeML]
      #6223578 - 11/29/13 02:51 PM

SCT's are for the most part, the equivalent of a Ford Focus or some other car costing around $10K-15K.

They fill the need of people needing to get around to work, shopping kids from school and the occasional road trip. Good all around. Inexpensive, able to do most things well but not outstandingly.

SCTs are the telescopic version. A good scope to learn on and is all most people will ever need. Does imaging and visual; is easy to maintain and keep clean; and is useable most of the time.

Newtonians have the edge for imaging faint objects visually but are heavier and need more adjusting; Maksutovs also stay cleaner and well adjusted and are heavier and more expensive; corrected D/K's and R/C's are suited for demanding imaging with higher costs and less utility for visual use


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kkokkolisModerator
Carpal Tunnel
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Reged: 09/23/09

Loc: Piraeus, Greece
Re: Why do people even buy SCTs??? new [Re: jimbo728]
      #6223597 - 11/29/13 02:59 PM

SCTs (and all Cats) are in fact heavily moded Newtonians. Take a fast Newtonian, replace the secondary with a f/5 mirror, add a Schmidt lens to seal the tube, voilà. Then open the tube because sealing brings problems, add fans, then dew heaters, then dew shields (that make them long again) and ofcourse focal reducers to make fast again what you made slow. Fast again but with added glass! Then add a refractor/ finder for widened views and a diagonal to replace the removed diagonal/ secondary. You still see a reversed image! Have an Amici somewhere close for terrestrial. Find a capable mount. Now add Ethos corrected to f/4 although your SCT isn't f/4 at all. Or remove the secondary to make it fast again for astrophotography. Oh! I forgot the coatings! Add coatings. And the glass should be good. Beware not to brake it.
Now you have your SCT.
And you start moding it. Bob's knobs is just for start.
Somewhere in the moding process, one might make it a Newtonian again!


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: Footbag]
      #6223600 - 11/29/13 03:03 PM

built quality?
be more real. look at interferometer test on mr. Rohr or on VAGO - these objectively show us most SCT "quality" - strehl ratio even without central obstruction be about 0.5 !
http://fidgor.narod.ru/Observers/Test/test_104.html
http://fidgor.narod.ru/Observers/Test/test_22.html
http://fidgor.narod.ru/Observers/Test/test_30.html

yes, there are some exemplars who show strehl about 0.85 and up, even 0.96 or so - but when we count central obstruction, who in general is larger than on newtonians, big problem with thermal equilibrium, a rough corrector plate plishing and so on - SCT have no chances to good newtonian, imho.


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WesC
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Reged: 02/06/13

Loc: La Crescenta, CA
Re: Why do people even buy SCTs??? new [Re: kkokkolis]
      #6223608 - 11/29/13 03:08 PM

I don't agree with that. SCTs and Newtonians are very different designs. They work differently, run differently and have different pros and cons. The only similarities are that they are folder optics and need to be collimated. But even those similarities are different.

Nope. Apples to pomegranates.


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Footbag
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Reged: 04/13/09

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Re: Why do people even buy SCTs??? new [Re: drago]
      #6223609 - 11/29/13 03:08 PM

Quote:

built quality?

SCT have no chances to good newtonian, imho.




So... What is a good Newtonian?

Strehl doesn't matter if your focuser cannot hold your CCD camera.


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WesC
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Reged: 02/06/13

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Re: Why do people even buy SCTs??? new [Re: Footbag]
      #6223611 - 11/29/13 03:11 PM

And for every link you post showing a bad SCT. I can post an excellent one.

This proves NOTHING!!!!!


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Why do people even buy SCTs??? new [Re: jimbo728]
      #6223629 - 11/29/13 03:26 PM

Even without a flocking mod - man I'm bonkers over my sct. I don't care about apo arguments and the like. For my dollar and effort - my c6 is a rock star.

You are right though Ed - the sct seems to get kicked like a whipping boy at times - particularly the C11 .

Pete


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rmollise
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Reged: 07/06/07

Re: Why do people even buy SCTs??? new [Re: kkokkolis]
      #6223633 - 11/29/13 03:29 PM

Quote:

SCTs (and all Cats) are in fact heavily moded Newtonians. Take a fast Newtonian, replace the secondary with a f/5 mirror,




Well...kinda...sorta...not really. The primary mirrors are different...the Newt's primay, unless it is of a very high focal ratio, must be a parabola. The SCT's is a sphere. And the secondary is not an "f/5 mirror," it is a convex mirror that magnifies 5x. It would be just as correct to say the Newtonian is a simplification of the earlier Cassegrain design.


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kansas skies
sage


Reged: 12/02/12

Loc: Kansas, USA
Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6223637 - 11/29/13 03:32 PM

As for me, I really don't care for the Dobsonian design. I like the motorized equatorial tracking (although a mechanical clock drive would be cool). For this reason, I find the 8" SCT to be a perfect setup for adequate aperture and portability. The key here, as someone already mentioned, is proper collimation. I might add that I have nothing against Newtonians, and I really would like one day to build something in the 16" to 20" range. If and when I do, it will have either a driven fork or a driven yoke equatorial mount.

Bill


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crow
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Reged: 07/09/12

Loc: BC, Canada
Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6223662 - 11/29/13 03:46 PM

I honestly think a lot of refractor heads worry about the performance of a good sct as great optics in combo with a large amount of aperture you'd have an ideal scope. Just as portable in many respects, I think my 1100 Edge weighs as much as a TOA130, pretty easy to handle.

You pay a hell of a lot for a good refractor so SCT's have to be bad lets face it.

If you find a good one, which is far easier than its made out, stick some fans in it or buy a cooler and enjoy. Some simple cooling is about all you need. learn how to Collimate it, so as not to be intimidated and thats it.

I enjoy a good 4' refractor too, to me its the ideal combo.


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6223663 - 11/29/13 03:46 PM

Quote:

Quote:



they cannot hold even against cheaper newtonians. newtonians have smaller central obstruction, less light loss and scatter taht catadioptrics. imho only cat's pluss in general is their compact size. all another compared to newtonians and refractors, is minuses...




Newtonians are fine if you just want to look. If you decide you want to do more than that, the SCT is far more versatile and adaptable.



Possibly if you are talking about the Average SCT's of years back. But the Quality of todays Schmidts are MUCH more consistent, and I firmly believe better.
My C6 SCT regularly performs up to my Criterion RV6.
There was a Time when I'd never have believed it.
I have never owned a 9.25, but My opinion of the Celestron C6 is that it is the perfect scope. Portable, and enough Horses under the hood to perform with the Big boys!
I also agree with Rod, they are far more flexible than a Newtonian. Binoviewing, Photography, Ease of transport,and other tangible features. Including the best deal for the money.
I used to love the C5, but it cannot compete with the C6, just like the C6 cant compete with an Edge 8.
Great thread guys!


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A6Q6
professor emeritus


Reged: 05/31/11

Loc: Stroudsburg,Pa,U.S.A
Re: Why do people even buy SCTs??? new [Re: azure1961p]
      #6223668 - 11/29/13 03:51 PM

Ok Pete and Eddgie, Whats up with the "flocking mod", what will it do for my old classic orange tube C5 that I'm having so much fun with? What do I have to do and is it really worth It?

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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6223677 - 11/29/13 03:54 PM

I used a C8 only for about 10 years. It served me well. For the past 18 years, I have viewed only with Dobs. For viewing only, I agree, at least for me, that the Dob is the better choice. For AP? Probably refractors or SCTs or MAKs.

I see one important question in all this: over the years, why haven't manufacturers made adjustments and upgrades to the SCT? The Edge and AC optics are an improvement; but, I believe many more could have been done. Mirror cool down issues alone would keep me from buying another SCT. True, you can make the modifications yourself. But, why not build them in? Doing so would increase the cost? Yes, but modifying an SCT also costs, and many people would find making their own modifications to be a daunting task.


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kkokkolisModerator
Carpal Tunnel
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Reged: 09/23/09

Loc: Piraeus, Greece
Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6223700 - 11/29/13 04:11 PM

Quote:

Quote:

SCTs (and all Cats) are in fact heavily moded Newtonians. Take a fast Newtonian, replace the secondary with a f/5 mirror,




Well...kinda...sorta...not really. The primary mirrors are different...the Newt's primay, unless it is of a very high focal ratio, must be a parabola. The SCT's is a sphere. And the secondary is not an "f/5 mirror," it is a convex mirror that magnifies 5x. It would be just as correct to say the Newtonian is a simplification of the earlier Cassegrain design.




I was joking ofcourse. Lost, perhaps, in translation.


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Kon Dealer
professor emeritus


Reged: 01/05/11

Loc: Cambridge UK
Re: Why do people even buy SCTs??? new [Re: GeneT]
      #6223728 - 11/29/13 04:31 PM

I love my 6SE. My 8SE gives even better views.
That said I use my 4" refractor more than the 6 and 8SE put together.
The basic problem is at 52 North the seeing raely supports over 150x. That along with cooling..
Still for the occassional times the SCTs are well worth it.


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azure1961p
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Reged: 01/17/09

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Re: Why do people even buy SCTs??? new [Re: drago]
      #6223731 - 11/29/13 04:32 PM

Quote:

built quality?
be more real. look at interferometer test on mr. Rohr or on VAGO - these objectively show us most SCT "quality" - strehl ratio even without central obstruction be about 0.5 !
http://fidgor.narod.ru/Observers/Test/test_104.html
http://fidgor.narod.ru/Observers/Test/test_22.html
http://fidgor.narod.ru/Observers/Test/test_30.html

yes, there are some exemplars who show strehl about 0.85 and up, even 0.96 or so - but when we count central obstruction, who in general is larger than on newtonians, big problem with thermal equilibrium, a rough corrector plate plishing and so on - SCT have no chances to good newtonian, imho.




Ill say one thing about the two Parks interfero's I've seen of scopes Ive owned - the d---ned lines are STRAIGHT. None of this swirly swaying grass in the wind garbage. I feel bad for anyone owning those mirrors - not that I haven't had equal or worse in the past.

Ill tell you though - the optician who opens shop with the offer of straightening out those poor sct optics will have his work cut out.
At anyrate I can't believe the C6 I have would put out the whimsical interferograms linked to.

Pete


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Jon Isaacs
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Re: Why do people even buy SCTs??? new [Re: orion61]
      #6223758 - 11/29/13 04:52 PM

Quote:

I also agree with Rod, they are far more flexible than a Newtonian. Binoviewing, Photography, Ease of transport,and other tangible features. Including the best deal for the money.




My first serious scope was an orange tube C-8. Since then I have owned a Meade 8 inch and two 5 inch Celestron as well as setup alongside many SCTs. Just a few thoughts:

In the smaller sizes, SCT's are easier to transport but this is not true once the scopes are large enough that a Truss Dobsonian makes sense. Setup, that depends on the mount.. But typically a Dobsonian is more easily setup but part of that is simplicity of the mount. A 16 inch Dob can be an easy one person setup, a 25 inch is still a one person setup. A 16 inch SCT is not really a portable, one person setup... 25 inch SCTs, they just don't exist as portable scopes.

Versatility, flexibility: At the eyepiece, Newtonians are more versatile, more flexible, they cover a wider range of magnifications, they can compete with refractors in terms of low power, wide field views. My 130mm F/5 will do 3.7 degree TFoV. That is not happening with an SCT.

Binoviewing, as Eddgie is doing, is possible with a Newtonian as is photography though probably not as easily done as with an SCT.

Jon


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jgraham
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Re: Why do people even buy SCTs??? new [Re: Jon Isaacs]
      #6223990 - 11/29/13 06:37 PM

Hmmm, I love my SCTs. They are the best general purpose scopes that I own. None of mine have been modified in any way.

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orion61

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Re: Why do people even buy SCTs??? new [Re: azure1961p]
      #6223999 - 11/29/13 06:42 PM

Quote:

Quote:

built quality?
be more real. look at interferometer test on mr. Rohr or on VAGO - these objectively show us most SCT "quality" - strehl ratio even without central obstruction be about 0.5 !
http://fidgor.narod.ru/Observers/Test/test_104.html
http://fidgor.narod.ru/Observers/Test/test_22.html
http://fidgor.narod.ru/Observers/Test/test_30.html

yes, there are some exemplars who show strehl about 0.85 and up, even 0.96 or so - but when we count central obstruction, who in general is larger than on newtonians, big problem with thermal equilibrium, a rough corrector plate plishing and so on - SCT have no chances to good newtonian, imho.




Ill say one thing about the two Parks interfero's I've seen of scopes Ive owned - the d---ned lines are STRAIGHT. None of this swirly swaying grass in the wind garbage. I feel bad for anyone owning those mirrors - not that I haven't had equal or worse in the past.

Ill tell you though - the optician who opens shop with the offer of straightening out those poor sct optics will have his work cut out.
At anyrate I can't believe the C6 I have would put out the whimsical interferograms linked to.

Pete



About every 6-8 months someone dredges up those toilet test results.
The worst of the worst. It's a wonder they don't dig up every bad Dynamax that has been sold and resold on EBAY!
Why don't you show some of the bad mirrors from Cave that went out in the last year or so. Sad fact. I love those old Caves, and Criterion, Parks, Edmund so on, and on.
Anyone is more than welcome to stop by and compare the views from my RV6 and C6.. at least there are no annoying diffraction spikes, or in the case of the RV6, (big clips) 6 of them. I will never sell my old criterion, I love it, but it is much more limited and frankly a pain to move and
use, Especially in the slightest of breezes.
Set minds are just that. A Donkey sitting in the middle of the road..
I used to be one of them...


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jrbarnett
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6224004 - 11/29/13 06:45 PM

I can think of just one reason, really, but it's a pretty good one. SCTs offer an attractive tube-length-per-unit-of-aperture (TLPUA) ratio. How else are you going to fit an 8" mirror into a 16" long package?

- Jim


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kkokkolisModerator
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Re: Why do people even buy SCTs??? new [Re: jrbarnett]
      #6224017 - 11/29/13 06:55 PM

Show character gentlemen!
That's why there all these types of telescopes. To satisfy everyone. No need to get angry.
The op was humorous anyway, we should respect the spirit of this thread IMHO.


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ATM57
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6224026 - 11/29/13 07:01 PM Attachment (44 downloads)

Quote:


Modders, please do not take offense. This is not directed at any individual. Rather it is just a rant about how so many people perceive so much wrong with a design that I have loved dearly over the decades, but now feel as if may be damaged by the perception that there is so much wrong with them.. So sad. Great telescopes.

At least one person loves them just the way they are...




Interesting rant As a modder, I agree that SCT's can be great instruments in standard form. When I mod one, that's what I start with: A GOOD ONE. I don't know about the other modders out there but some of my reasons for performing such things are:

1. If there is extra performance to be had I want it. (I do the same with OTHER TELESCOPE DESIGNS and computers)

2. I enjoy the challenge of making things perform better if possible. As an example, I once had a 80mm refractor that was an excellent performer but one simple tweak made it perform better. The retaining ring on the lens was too tight. Once loosened, I was able to see the companion to Rigel much easier than before under the same conditions.

3. I love the shock factor when I can clearly demonstrate that SCT's can be made to perform better for lunar, planetary, multiple star work than manufactured. As we all know, they are designed to satisfy many types of astronomical uses. You have to make some compromises if you are going to be a Jack-of-all-Trades. I turn them into speciality instruments.

4. I like having a unique telescope (like putting personal touches on your car) it sets your instrument apart from the crowd.

I could go on but...

The pic shows a basket case scope I once received. It had excellent optics but came with a lot of minor dents, scrapes and scratches. I modded this scope with passive cooling and eliminated the dents in the process. Custom covers were made for the vents. This scope is an excellent performer.

My mods are not performed to "put down" a design be it refractor, reflector or compound instrument. I just like making scopes perform better. Nothing more. Nothing less.

Scopejunkie


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Awesomelenny
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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6224044 - 11/29/13 07:14 PM

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!

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azure1961p
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Re: Why do people even buy SCTs??? new [Re: kkokkolis]
      #6224118 - 11/29/13 08:16 PM

Whose angry? I thought its been fairly good thread. Differing opinions here and there but nothing Id call anger. And the spirit of the OP was tongue n cheek anyway.

Pete


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Asbytec
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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6224140 - 11/29/13 08:28 PM

I agree totally with scopejunkie. If there is extra performance to be had, I want it. I love my own CAT as is, but if it can be better, "I want it." Its like owning a nice muscle car and taking time to tune it so it runs as good as it can run. Racing is all about those fine tuning tweaks and does not speak the quality of the underlying build, per se. When you're reaching for that additional photon, a fine tuning mod may give it to you. In fact, I liked my own so much (straight out of the box), I took the time and effort to study it and to fine tune it for maximum RPMs. We cruise the skies nightly. Even well built vintage US muscle cars can be faster than stock. So, really modding is not a detriment to the versatile SCT package, IMO. I've never been unhappy with any SCT I've owned and thoroughly enjoy my current 6" CAT...before and after modding it.

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ATM57
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Re: Why do people even buy SCTs??? new [Re: Awesomelenny]
      #6224161 - 11/29/13 08:37 PM

Quote:

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie


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bremms
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Re: Why do people even buy SCTs??? new [Re: Jon Isaacs]
      #6224192 - 11/29/13 08:56 PM

I have two good SCTs. My 6" F8 Newtonian and 6" F10 achro outperform my C8 on most objects. The 6" Newtonian is a no contest..Hands down better at everything other than a little light gathering. I use my SCTs a bit. When take you into account so so optics (even good ones) field curvature, significant coma, limited FOV.... I like them for what they are. Portable aperature. Clever design. A friend and I tested three on an interferometer. Best one was just 1/2 wave p-v. Worst was about 1 wave. That was an SP C8. Another friend just bought. We managed to send it back and get another( that was the 1/2 wave). The C8s are very inexpensive for such a complex optic. They are just not going to be Zeiss quality.
I like my C8 and it has good optics for a C8. But it can't compete with a 6" newt with a 1/11wave PV mirror and small CO.


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ur7x
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Re: Why do people even buy SCTs??? new [Re: Awesomelenny]
      #6224194 - 11/29/13 08:57 PM

Quote:

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




I've had and still have them all. My 9.25 SCT kicks my F/5 6" Newts backside. So much so that the newt will likely soon be stored in a plastic box in the attic... And my newt came flocked from the factory

Put me down in the love my SCT and I have zero desire to take it apart and mess with it. It is already by far better than anything that I have tried to improve.


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ATM57
sage


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Loc: Tehachapi, CA
Re: Why do people even buy SCTs??? new [Re: Asbytec]
      #6224195 - 11/29/13 08:58 PM

Quote:

I agree totally with scopejunkie. If there is extra performance to be had, I want it. I love my own CAT as is, but if it can be better, "I want it." Its like owning a nice muscle car and taking time to tune it so it runs as good as it can run. Racing is all about those fine tuning tweaks and does not speak the quality of the underlying build, per se. When you're reaching for that additional photon, a fine tuning mod may give it to you. In fact, I liked my own so much (straight out of the box), I took the time and effort to study it and to fine tune it for maximum RPMs. We cruise the skies nightly. Even well built vintage US muscle cars can be faster than stock. So, really modding is not a detriment to the versatile SCT package, IMO. I've never been unhappy with any SCT I've owned and thoroughly enjoy my current 6" CAT...before and after modding it.




Excellent perspective

Scopejunkie


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: WesC]
      #6224199 - 11/29/13 08:58 PM

Quote:

And for every link you post showing a bad SCT. I can post an excellent one.

This proves NOTHING!!!!!




Is that true today? Less than a decade ago, there wasn't one C-11 I tested that I'd keep. If they're better now, perhaps it's time to pick up one or a C-14 and add a Hyperstar unit & camera on it.


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JJK
Carpal Tunnel


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Re: Why do people even buy SCTs??? new [Re: Awesomelenny]
      #6224206 - 11/29/13 09:01 PM

Quote:

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




If you want aperture, get a Dob-Newt.


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JJK
Carpal Tunnel


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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6224209 - 11/29/13 09:03 PM

Quote:

Quote:

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie




While SCTs have their virtues, it would take much less than a 9" refractor to outperform a 9" SCT.


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ATM57
sage


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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224268 - 11/29/13 09:39 PM

Quote:

Quote:

Quote:

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie




While SCTs have their virtues, it would take much less than a 9" refractor to outperform a 9" SCT.




Not mine.

Scopejunkie


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Dwight J
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224272 - 11/29/13 09:40 PM

I wonder why then so many of the best planetary imagers and images use and are taken by C11's and 14's. Must be their low contrast, huge obstruction, and mushy optics. Oh, I almost forgot their eons long cooling time.

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dscarpa
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6224293 - 11/29/13 09:57 PM

The only issues my regular C9.25 has is a bit of image shift, a little coma and on a humid night it dews up before I can get it out the door. My scopes mount's a push to Unistar so no power but there's always a hair drier standing by! There's a lot less coma with the SCT than my new 11" F/5 newt without it's corrector. The newt has a high end mirror and should out perform the SCT with ease but what with viewing seated comfortably with the cat vs not sure yet with the newt that might not be the case for lunar-planetary in particular. On excellent nights I've used the C9.25 at 400X on Jupiter and 500X-550X on the Moon, Saturn and Mars with very detailed, crisp, bright high contrast images! David

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JJK
Carpal Tunnel


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Re: Why do people even buy SCTs??? new [Re: Dwight J]
      #6224341 - 11/29/13 10:40 PM

Quote:

I wonder why then so many of the best planetary imagers and images use and are taken by C11's and 14's. Must be their low contrast, huge obstruction, and mushy optics. Oh, I almost forgot their eons long cooling time.




I didn't say decent SCTs don't exist. As I alluded to above, I've been looking to add one to my visual scope aresenal, but stopped a decade or so ago because none I critically tested (C-11s) could be pushed over 250 x on nights that my AP Mak-Cass was easily able to work well at 400 to 600 x. I'm thinking of looking again with the advent of Hyperstar. Looks like a lot of fun.


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JJK
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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6224351 - 11/29/13 10:42 PM

Quote:

Quote:

Quote:

Quote:

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie




While SCTs have their virtues, it would take much less than a 9" refractor to outperform a 9" SCT.




Not mine.

Scopejunkie




Which 9" refractors did you test your 9" SCT against, and on which targets?


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jgraham
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224388 - 11/29/13 11:19 PM

I've got my 10" SCT outside right now taking images of Jupiter. Simply freek'n awesome.

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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224404 - 11/29/13 11:33 PM

TOP TEN REASONS WE LOVE OUR SCTs

1..Because they are great scopes!

2..As far as comfort goes, no other scope comes close!

3..They also are more steady per pound than a GEM of the same aperture! (for the same amount of money)

4..They are also lighter per aperture than most any other computer driven scope!

5..With a day or two of work, they can be as good as almost any other design could possibly be, with the same amount of CO that is! (A Good Unit)

6..They look great! Who wants to use an ugly scope? Not me.

7..They are the most convenient!

8..There are all kinds of accessories for them!

9..They do visual, they do photography!

10..They don't cost an arm and a leg and a child to own!

So, all things considered, what's not to like???


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ATM57
sage


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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224406 - 11/29/13 11:37 PM Attachment (18 downloads)

Quote:

Quote:

Quote:

Quote:

Quote:

I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie




While SCTs have their virtues, it would take much less than a 9" refractor to outperform a 9" SCT.




Not mine.

Scopejunkie




Which 9" refractors did you test your 9" SCT against, and on which targets?




I have built 3 8" refractors. Two at F/12 and 1 at F/9. I know how 8" refractors perform and would compare to my modified C-9.

Scopejunkie

Edited by ATM57 (11/29/13 11:43 PM)


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BYoesle
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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6224455 - 11/30/13 12:34 AM

Great, just what we need: another petty and ridiculous sectarian divide.

First, let me say I’ve owned all kinds of telescopes. I don’t think it appropriate to disparage a particular type of telescope, as they all have their pluses and minuses. SCTs offer a large aperture in a compact size, among other advantages. However, they can also have their limitations and issues, and indeed often can be made to perform even better by modifying them – both optically and mechanically. Where does the concept of “believing in their SCTs” (or any telescope for that matter) come into play? Perhaps I’m just an atheist when it comes to material objects, or at least telescopes

That said, I’m having a little trouble understanding your post Ed.

Quote:

I have just been so thrilled with my SCTs in the past. Most of them were really able telescopes that presented me with hundereds of hours of wonderful observing. And none of the mods I tried seemed to make any meaningful difference for my own observing needs that I stopped chasing the "Mod of the day" a long time ago. And the bigger I went, the more I enjoyed them. The more I could see. More deep sky, more planetary detail, more stars in clusters. No mods or anything. I just went bigger and bigger and saw more and more... At least one person loves them just the way they are...




If you were so thrilled with the SCT’s you had in the past and loved them just the way they are, why did you get an Edge HD as listed in the signature? Could it have been OTA/mirror venting, a new secondary mirror and corrective optics to eliminate coma and flatten the field, and a primary mirror clutch/lock to eliminate mirror shift?

It seems you have “voted with your feet” and abandoned the very scopes you love “just the way they are.” So if someone with an older version SCT attempts via modification to gain some of the same advantages you have obtained by buying an newer version of the SCT, doesn’t that mean you have simply paid to have the mods done for you rather than attempting them yourself? Hasn’t your very action demonstrated that which you are concerned with -- enhancing the perception that there is “so much wrong” with SCTs? If you have chosen a “better mouse trap” via a manufacturer, why shouldn’t someone try some of the same via modification of their existing scope -- without being subjected to the claim that they are denigrating the SCT?

Lastly, let me just say some of us like to tinker and experiment to see what improvements we can make on our own, and how the incremental improvements can add up...

Best wishes to one and all,


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EFT
Vendor - Deep Space Products
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Re: Why do people even buy SCTs??? new [Re: BYoesle]
      #6224477 - 11/30/13 12:52 AM

My first real scope was an SCT and I doubt that I will ever be without one. They may not be perfect, but that cannot be beat for size, performance AND price. I have yet to feel the desire to haul around a 6-foot plus tube or a hugely heavy collapsible newt that must be completely disassembled for transport. Someday maybe, but I still won't give up my SCT. Nothing wrong with modding them to improve the performance, but even that may not be necessary depending on where you use the scope.

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azure1961p
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Re: Why do people even buy SCTs??? new [Re: BYoesle]
      #6224504 - 11/30/13 01:36 AM

Quote:

Great, just what we need: another petty and ridiculous sectarian divide.

First, let me say I’ve owned all kinds of telescopes. I don’t think it appropriate to disparage a particular type of telescope, as they all have their pluses and minuses. SCTs offer a large aperture in a compact size, among other advantages. However, they can also have their limitations and issues, and indeed often can be made to perform even better by modifying them – both optically and mechanically. Where does the concept of “believing in their SCTs” (or any telescope for that matter) come into play? Perhaps I’m just an atheist when it comes to material objects, or at least telescopes

That said, I’m having a little trouble understanding your post Ed.

Quote:

I have just been so thrilled with my SCTs in the past. Most of them were really able telescopes that presented me with hundereds of hours of wonderful observing. And none of the mods I tried seemed to make any meaningful difference for my own observing needs that I stopped chasing the "Mod of the day" a long time ago. And the bigger I went, the more I enjoyed them. The more I could see. More deep sky, more planetary detail, more stars in clusters. No mods or anything. I just went bigger and bigger and saw more and more... At least one person loves them just the way they are...




If you were so thrilled with the SCT’s you had in the past and loved them just the way they are, why did you get an Edge HD as listed in the signature? Could it have been OTA/mirror venting, a new secondary mirror and corrective optics to eliminate coma and flatten the field, and a primary mirror clutch/lock to eliminate mirror shift?

It seems you have “voted with your feet” and abandoned the very scopes you love “just the way they are.” So if someone with an older version SCT attempts via modification to gain some of the same advantages you have obtained by buying an newer version of the SCT, doesn’t that mean you have simply paid to have the mods done for you rather than attempting them yourself? Hasn’t your very action demonstrated that which you are concerned with -- enhancing the perception that there is “so much wrong” with SCTs? If you have chosen a “better mouse trap” via a manufacturer, why shouldn’t someone try some of the same via modification of their existing scope -- without being subjected to the claim that they are denigrating the SCT?

Lastly, let me just say some of us like to tinker and experiment to see what improvements we can make on our own, and how the incremental improvements can add up...

Best wishes to one and all,




I think you mis took his intent.

Pete


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6224509 - 11/30/13 01:46 AM

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I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie




While SCTs have their virtues, it would take much less than a 9" refractor to outperform a 9" SCT.




Not mine.

Scopejunkie




Which 9" refractors did you test your 9" SCT against, and on which targets?




I have built 3 8" refractors. Two at F/12 and 1 at F/9. I know how 8" refractors perform and would compare to my modified C-9.

Scopejunkie




Did you grind the lenses, what style (achro, apo) where they, and what were the specifications of the objectives (smoothness, zones, coatings)?


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ATM57
sage


Reged: 01/01/10

Loc: Tehachapi, CA
Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224519 - 11/30/13 02:03 AM

Quote:

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I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie




While SCTs have their virtues, it would take much less than a 9" refractor to outperform a 9" SCT.




Not mine.

Scopejunkie




Which 9" refractors did you test your 9" SCT against, and on which targets?




I have built 3 8" refractors. Two at F/12 and 1 at F/9. I know how 8" refractors perform and would compare to my modified C-9.

Scopejunkie




Did you grind the lenses, what style (achro, apo) where they, and what were the specifications of the objectives (smoothness, zones, coatings)?




I won't go into the details concerning the three 8" refractors I have built. That's not the reason for this thread. I will say that the lenses were tested before I built scopes around them though.

Scopejunkie


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doug mc
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Re: Why do people even buy SCTs??? new [Re: jrbarnett]
      #6224520 - 11/30/13 02:04 AM

I thought , what would be better than my c6---- you got it , a c8. So i went and got one. Happy camper. Versatile, comfortable viewing on a stool, no need for hyper expensive eyepieces, yada yada, the list goes on.

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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: Footbag]
      #6224537 - 11/30/13 02:25 AM

Quote:

Quote:

built quality?

SCT have no chances to good newtonian, imho.




So... What is a good Newtonian?

Strehl doesn't matter if your focuser cannot hold your CCD camera.




i there talking about visual instrument. if we talking about a photographic, then statements is another. large central obstruction and mediocre optics quality there are no problem...


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kkokkolisModerator
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Re: Why do people even buy SCTs??? new [Re: azure1961p]
      #6224542 - 11/30/13 02:38 AM

Quote:

Whose angry? I thought its been fairly good thread. Differing opinions here and there but nothing Id call anger. And the spirit of the OP was tongue n cheek anyway.

Pete




I wish, hope and consider that you are right. I'm happy as long as I am wrong!


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AlaskaWolf
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Loc: Meridian, ID
Re: Why do people even buy SCTs??? new [Re: jimbo728]
      #6224573 - 11/30/13 03:46 AM

10-in. F/12.0 Alpha Draconis Apochromatic OTA: $91,280 (used to be a naval gun)
OR
Celestron CGE PRO 1100 EdgeHD : $6,999

Yeah...I think I can deal with the SCT's faults, buy a new F-350, take that vacation to Bora Bora, and get change back

I love refractors...but if I want to see something that big, I'll just head on down to Mobile with Uncle Rod and visit the USS Alabama....


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Jon Isaacs
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Re: Why do people even buy SCTs??? new [Re: ur7x]
      #6224576 - 11/30/13 03:47 AM

Quote:

My 9.25 SCT kicks my F/5 6" Newts backside.




I imagine it does when it comes to working at high magnifications, it ought to. However there are places a 6 inch F/5 will go that a 9.25 inch F/10 cannot and that's the reason to own both these scopes. One of them is capable of a 3 degree field of view, one of them is capable of a 1 degree field of view..

The right scope for the job at hand is what it all about. There are objects that are best suited for an 80mm F/5 with a 2 inch focuser, there are objects that are best suited for a 635mm aperture.. The California nebula is not much to look at in a 0.7 degree TFoV.

Jon


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Jon Isaacs
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Re: Why do people even buy SCTs??? new [Re: EFT]
      #6224584 - 11/30/13 03:58 AM

Quote:

My first real scope was an SCT and I doubt that I will ever be without one. They may not be perfect, but that cannot be beat for size, performance AND price. I have yet to feel the desire to haul around a 6-foot plus tube or a hugely heavy collapsible newt that must be completely disassembled for transport




A data point:

I used to setup my 12.5 inch Tube Dob alongside a variety of guys with 12 inch LX-200s. I could do it in less than a minute, the tube was about 51 inches long... I never did see someone setup a 12 inch LX-200 in less than a minute...

Jon


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David Knisely
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Re: Why do people even buy SCTs??? new [Re: Jon Isaacs]
      #6224586 - 11/30/13 04:02 AM

Quote:

Quote:

My 9.25 SCT kicks my F/5 6" Newts backside.




I imagine it does when it comes to working at high magnifications, it ought to. However there are places a 6 inch F/5 will go that a 9.25 inch F/10 cannot and that's the reason to own both these scopes. One of them is capable of a 3 degree field of view, one of them is capable of a 1 degree field of view..

The right scope for the job at hand is what it all about. There are objects that are best suited for an 80mm F/5 with a 2 inch focuser, there are objects that are best suited for a 635mm aperture.. The California nebula is not much to look at in a 0.7 degree TFoV.

Jon




Well, the California Nebula is not much to look at in scopes with even a two to 2.5 degree true field of view. To see the whole thing, I need my 100mm f/6 refractor. Still, in my 9.25 inch SCT (59x, 1.12 degree true field of view) using the H-Beta filter at my dark sky site, I can see some of the broad filamentary detail in that nebula by panning around somewhat.

As for the question about why people buy SCT's, the answer is plain: Because they WORK! They may not be exactly the very best in certain areas, but they can be a very effective instrument for the amateur astronomer (I know mine is). Clear skies to you.


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junomike
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Re: Why do people even buy SCTs??? new [Re: David Knisely]
      #6224671 - 11/30/13 07:19 AM

SCT ~ Sufficient Compact Telescope.

The "Jack of all trades, master of none."

Mike


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Wmacky
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6224704 - 11/30/13 08:12 AM

Quote:

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built quality?

SCT have no chances to good newtonian, imho.




So... What is a good Newtonian?

Strehl doesn't matter if your focuser cannot hold your CCD camera.




i there talking about visual instrument. if we talking about a photographic, then statements is another. large central obstruction and mediocre optics quality there are no problem...




Who said this thread was only about visual? I don't care for ugly diffraction spikes, inherent coma which the Edge scopes lack. Limited back focus. You every look through a Newtonian while on a GEM? Was the focuser stuck underneath the scope? And no you can't use a dob mount if you have a observatory with a centrally mounted GEM unless you want to get stuck using only one scope. What's the current most used scope for Planetary imaging? I had to give away my last newtonian as the coating flaked off do to humidity exposure after 7years out in the observatory. That's what happens to unprotected mirrors in this location.

Now all that said, I DO like newtonians,and plan for a big Dob in the future, but if you think that size is the only advantage to a SCT's, well........

Edited by Wmacky (11/30/13 08:33 AM)


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kansas skies
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Reged: 12/02/12

Loc: Kansas, USA
Re: Why do people even buy SCTs??? new [Re: Jon Isaacs]
      #6224743 - 11/30/13 08:37 AM

Quote:

Quote:

My first real scope was an SCT and I doubt that I will ever be without one. They may not be perfect, but that cannot be beat for size, performance AND price. I have yet to feel the desire to haul around a 6-foot plus tube or a hugely heavy collapsible newt that must be completely disassembled for transport




A data point:

I used to setup my 12.5 inch Tube Dob alongside a variety of guys with 12 inch LX-200s. I could do it in less than a minute, the tube was about 51 inches long... I never did see someone setup a 12 inch LX-200 in less than a minute...

Jon




Are you not comparing apples to oranges here? I'm assuming that beyond the optics comparison, there's also the alt-az vs equatorial comparison. How much difference in setup time would there be if the mountings were similar?

Bill


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: Wmacky]
      #6224753 - 11/30/13 08:43 AM

Quote:

Quote:

Quote:

Quote:

built quality?

SCT have no chances to good newtonian, imho.




So... What is a good Newtonian?

Strehl doesn't matter if your focuser cannot hold your CCD camera.




i there talking about visual instrument. if we talking about a photographic, then statements is another. large central obstruction and mediocre optics quality there are no problem...




Who said this thread was only about visual? I don't care for ugly diffraction spikes, inherent coma which the Edge scopes lack. Limited back focus. You every look through a Newtonian while on a GEM? Was the focuser stuck underneath the scope? And no you can't use a dob mount if you have a observatory with a centrally mounted GEM unless you want to get stuck using only one scope. What's the current most used scope for Planetary imaging? I had to give away my last newtonian as the coating flaked off do to humidity exposure after 7years out in the observatory. That's what happens to unprotected mirrors in this location.

Now all that said, I DO like newtonians,and plan for a big Dob in the future, but if you think that size is the only advantage to a SCT's, well........




i have more concentradet on visual side, and as a result, i decide from that side. that's is psychological point \ trap
about photo - i can agree, there rules even a RC of CO about 50 percent or so on.
but on visual side - yes, i too not like a diffraction spikes, and my favorite optical system is the superrior system - refractors. most close to "ideal scope" from all sides.
but its size ( aperture) is limited, and prices, weights and gabarits grow skyhigh as aperture reaches about 200mm.
second good system is newtonian - larges apertures, but manageable, small weights, prices, relatively small central obstruction, and possibility to get high strehl numbers on whole telescope.
on GEM it is not good, i agree - i have orion optics europe 200 on EQ5, and can confirm - most of poses is very uncomfortable. but dobsonian mount, as i hear and imagine, is very good for this, as so i not see a problem, unless a GEM is a thing, without who you cannot living at all...
a catadioptrics in that matter, as there is always said, is "jack of all trades, and in all trades he give a bad result"...:D


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bobhen
professor emeritus


Reged: 06/25/05

Re: Why do people even buy SCTs??? new [Re: drago]
      #6224914 - 11/30/13 10:37 AM

I use my 11 inch Celestron mostly for what Tom Johnson intended – “astro-friendly” photography. Well, these days it’s video viewing. Their compact (with all the advantages compactness brings), have many available accessories, with video can be made to work from F2 to F20, and they don’t need to be super high quality to deliver great results. Thank you Mister Johnson.

My other 5 telescopes are all refractors – for all the right reasons.

Bob


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6224943 - 11/30/13 11:03 AM

Quote:

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I have had all ... refractors, apo's, reflectors, SCT's and sorry, aperture rules! A really sweet scope like my Meade 14"ACF is awesome. Imagine having a 14" refractor, oh my goodness, I'd need a crane to haul THAT around!




Yeah, a 14" refractor would be a monster to be sure even if it was an APO. My C-9 is currently satisfying my large planetary scope needs. A 9" refractor could not be afforded even if I built my own hence my "modded" C-9. We all satisfy our needs in different ways.

Scopejunkie




While SCTs have their virtues, it would take much less than a 9" refractor to outperform a 9" SCT.




Not mine.

Scopejunkie




Which 9" refractors did you test your 9" SCT against, and on which targets?




I have built 3 8" refractors. Two at F/12 and 1 at F/9. I know how 8" refractors perform and would compare to my modified C-9.

Scopejunkie




Did you grind the lenses, what style (achro, apo) where they, and what were the specifications of the objectives (smoothness, zones, coatings)?




I won't go into the details concerning the three 8" refractors I have built. That's not the reason for this thread. I will say that the lenses were tested before I built scopes around them though.

Scopejunkie




The answers would obviously help frame your earlier comment, but if you don't want to share them, that's your choice. Frankly, I think it's interesting to hear the lengths that some folks go through to build their own equipment. I wish I had the time to learn how to properly grind, polish, test, and coat refracting lenses with my own hands.

To my original point, I doubt a 9.25" (Celestron or Meade) SCT would outperform even a top-notch 7" apochromatic refractor (e.g., made by a company in the league of Astro-Physics or Zeiss). And that wouldn't stop me from considering one for purchase. However, I did not buy any 11" SCT I tested about a decade ago, because none of them performed well enough for the intended purpose (critical high magnification visual work). At that time, I didn't have interest in retrofitting them to see if it was a thermal issue.

In 1999, I critically tested Roland Christen's 8" and 10" Mak-Cass prototypes in very good seeing against his 180 mm and 200 mm class refractors (one was Sue & Alan French's scope that is a Moon killer). The test target was Saturn. The 8" Mak-Cass delivered images on par with the 7" apos, and the 10" just edged out the 8" refractor, but not by much. Given the compact nature of the Mak-Cass, I ordered a 10" varietal, and received it a few years later. When the seeing is good, that scope is stunning (it had better be for the list price of $10K), and I've never seen even an 11" SCT come anywhere close to this instrument's capability. I often use the Mak-Cass at 1000x to see the central star in the Ring Nebula, something I have not been able to accomplish with any 11" SCT. Roland's 10" Mak-Cass doesn't defy the laws of physics. When I want to hunt down very faint galaxies, I use a 25" Dob-Newt.

All that said, I don't expect a far lower cost SCT to perform at the same level of a much more expensive scope. However, I would like it to perform better than the ones I tested long ago. I'm in the market for one (or two).


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: Jon Isaacs]
      #6224947 - 11/30/13 11:05 AM

Quote:

Quote:

My 9.25 SCT kicks my F/5 6" Newts backside.




I imagine it does when it comes to working at high magnifications, it ought to. However there are places a 6 inch F/5 will go that a 9.25 inch F/10 cannot and that's the reason to own both these scopes. One of them is capable of a 3 degree field of view, one of them is capable of a 1 degree field of view..

The right scope for the job at hand is what it all about. There are objects that are best suited for an 80mm F/5 with a 2 inch focuser, there are objects that are best suited for a 635mm aperture.. The California nebula is not much to look at in a 0.7 degree TFoV.

Jon




I agree!


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224951 - 11/30/13 11:08 AM

Quote:

I often use the Mak-Cass at 1000x to see the central star in the Ring Nebula, something I have not been able to accomplish with any 11" SCT. Roland's 10" Mak-Cass doesn't defy the laws of physics. When I want to hunt down very faint galaxies, I use a 25" Dob-Newt.





very interested - looks like you have a 10" top quality mak, and 25" dob. do you try compare it both side by side on planets?


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JJK
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Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224952 - 11/30/13 11:09 AM

I'd like to add that I once critically viewed a C14 that performed very well. I was tempted to get one, but it was more scope than I thought I could handle at the time. I should have bought one.

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nicklane1
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Reged: 03/04/08

Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224955 - 11/30/13 11:10 AM

Eddgie, this is all tongue in cheek, right? Seems like you are just sitting back and letting others parry and counter parry.

I think you once said that you like your 8" EdgeHD so much that you hardly use your 6" A-P refractor anymore.


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EFT
Vendor - Deep Space Products
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6224992 - 11/30/13 11:32 AM

Quote:

All that said, I don't expect a far lower cost SCT to perform at the same level of a much more expensive scope. However, I would like it to perform better than the ones I tested long ago. I'm in the market for one (or two).




You need to try out an Edge HD.


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JJK
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Re: Why do people even buy SCTs??? new [Re: EFT]
      #6225051 - 11/30/13 12:03 PM

Quote:

Quote:

All that said, I don't expect a far lower cost SCT to perform at the same level of a much more expensive scope. However, I would like it to perform better than the ones I tested long ago. I'm in the market for one (or two).




You need to try out an Edge HD.




Thanks, I'll read up on them, and check them out at a star party. I had originally thought about getting an 11" SCT, but given that I got a 10" Mak-Cass, I'm now thinking of getting a 14" SCT I can share with a community.


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mmalik
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6225079 - 11/30/13 12:17 PM

Quote:

But these days, I am more inclined to recommend a small refractor. Nothing to do. Just plug and play.




This is where I have come to.

There is nothing wrong with SCTs until there is everything wrong with them and it has to do with what I refer to as their "shifty" nature; shifting collimation, shifting mirror, shifting focus/focuser, shifting cooling, shifting/bending corrector in HyperStar implementations, etc. SCTs don't seem to command the solidity that their counterparts do. This may not affect visual observing to the extent it does imaging. Regards


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johntrob
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Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6225089 - 11/30/13 12:21 PM

I love the balance of the SCT's. I can hang my raincoat over it as I come in the house and it does not move. Cannot do that with my refractor?

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ErikB
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6225116 - 11/30/13 12:36 PM

This debate is obviously being conducted by experienced people, as a lover's quarrel for the sake of having something to do and deepen the love for the subject. That is ok, as most of us come to forums just to waste some time of a favorite subject. Anyway, beginners will also be reading the thread, and with most posters taking a pro-sct stance, I will add my 2c not to fuel the tongue in cheek fun but for counterbalancing the extreme pro-sct statements made in jest. Some have said that sct's "are good for imaging". Meaning planetary, which is true. However, beginners need to know that good for planetary doesn't mean good for imaging other sky objects. The reason sct's are good for planetary imaging is that a planet needs extreme magnification (provided by the unusually long focal length) and extreme resolution, which is provided by the sct's big aperture, which is hard to match with a refractor. A newt can easily provide the aperture, but most of them these days don't provide as much focal length for a given aperture. Planets are very bright, which means exposure times generally are in the milliseconds. This means a mount good enough for visual is good enough for imaging planets. There is a reason for the saying that imagers spend more for the mount for the ota. If the mount is a GEM in the lower price range, it won't be steady enough for the long exposures needed for dim objects, except maybe for a very small sct. An sct on a cheap GEM is likely not steady enough to avoid vibration, and its periodic error may be difficult to correct for by guiding and/or PEC. A forked sct may in some cases be less prone to vibration, but may have totally unacceptable periodic error, and when you find out, you may notice that there is no easy way to replace the mount and keep the optics. Most objects do not require the extreme magnifications that planets do, so a refractor or newt provides a more suitable focal length, which is compatible with a somewhat affordable mount. Focal reducers for sct's have their own problems. Another problem with sct's for general astro imaging is contrast. Actually, contrast and resolution have to be considered together and not as separate specifications. By virtue of its large aperture the sct has high resolution, suitable for planetary imaging. However, contrast varies with the level of resolution you make use of. At the extreme resolution used for planetary imaging, the contrast of an sct tends to be very very low. Only aggressive computer processing brings up contrast to where we can see the tiniest details on the planet. Such processing tends to make things a bit unnatural. When we are looking for detail on a planet, we tend to be happy to see any at all, no matter if the image is unnatural. For most other objects, we don't need the extra magnification, and we may be better off with an instrument such as a refractor that provides better contrast without aggressive processing. Going to image tiny *and* dim objects? An SCT may be appropriate, but it had better be an Edge or ACF, and plan on spending the price of a new car on the mount. How about the visual observer? Here the convenient eyepiece position of an sct is wonderful, and if the fork mount has some jumps in the periodic error, it doesn't matter. The contrast generally doesn't match that of a refractor or newt, but again, contrast varies with resolution for a given scope. If a given detail doesn't show enough contrast in a given sct, that can be remedied with a bigger sct, which will have more contrast for a given scale of detail. Even the bigger sct may cost less than a refractor that shows the same detail comparably. I like my sct's for visual use, but I would not expect my old plain 8" to be able to resolve much at all in M13. Now, I have never tried an 8" Edge...

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ATM57
sage


Reged: 01/01/10

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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6225119 - 11/30/13 12:37 PM Attachment (21 downloads)

Quote:

Quote:

I won't go into the details concerning the three 8" refractors I have built. That's not the reason for this thread. I will say that the lenses were tested before I built scopes around them though.

Scopejunkie




The answers would obviously help frame your earlier comment, but if you don't want to share them, that's your choice. Frankly, I think it's interesting to hear the lengths that some folks go through to build their own equipment. I wish I had the time to learn how to properly grind, polish, test, and coat refracting lenses with my own hands.

To my original point, I doubt a 9.25" (Celestron or Meade) SCT would outperform even a top-notch 7" apochromatic refractor (e.g., made by a company in the league of Astro-Physics or Zeiss). And that wouldn't stop me from considering one for purchase. However, I did not buy any 11" SCT I tested about a decade ago, because none of them performed well enough for the intended purpose (critical high magnification visual work). At that time, I didn't have interest in retrofitting them to see if it was a thermal issue.

In 1999, I critically tested Roland Christen's 8" and 10" Mak-Cass prototypes in very good seeing against his 180 mm and 200 mm class refractors (one was Sue & Alan French's scope that is a Moon killer). The test target was Saturn. The 8" Mak-Cass delivered images on par with the 7" apos, and the 10" just edged out the 8" refractor, but not by much. Given the compact nature of the Mak-Cass, I ordered a 10" varietal, and received it a few years later. When the seeing is good, that scope is stunning (it had better be for the list price of $10K), and I've never seen even an 11" SCT come anywhere close to this instrument's capability. I often use the Mak-Cass at 1000x to see the central star in the Ring Nebula, something I have not been able to accomplish with any 11" SCT. Roland's 10" Mak-Cass doesn't defy the laws of physics. When I want to hunt down very faint galaxies, I use a 25" Dob-Newt.

All that said, I don't expect a far lower cost SCT to perform at the same level of a much more expensive scope. However, I would like it to perform better than the ones I tested long ago. I'm in the market for one (or two).




I didn't want to go into details because they were not needed. I'm not saying that all C-9's are as good as the one I have. Most SCT's are good but not exceptional. Every now and then you can get your hands on one that is on the "high end" in optical performance. I have owned a few.

With the right mods they can be made into excellent high power instruments. My point is: You don't have to mortgage your home to get top level high resolution performance.

I used to hate SCT's with a passion until I looked into why, with many of them, their performance was lacking. I discovered a lot of things that can make them bad. Some belong to the makers and some belong to the end user. How many times have Newtonians been compared to refractors over the years with many stating that refractors are superior?

My posts are for the tinkerers who lack the funds for high end iron and give them an alternative to costly apos and high end maks.

I have read here complaints against C-11's. That is strange to me since I have had some really good ones (and a few dogs). Just lucky I guess. The pic shows one that I put a lot of time into and should have never sold.

I enjoy the challenge of making them work well.

Scopejunkie


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rmollise
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Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6225244 - 11/30/13 01:49 PM

Quote:



There is nothing wrong with SCTs until there is everything wrong with them and it has to do with what I refer to as their "shifty" nature; shifting collimation, shifting mirror, shifting focus/focuser, shifting cooling, shifting/bending corrector in HyperStar implementations, etc. SCTs don't seem to command the solidity that their counterparts do. This may not affect visual observing to the extent it does imaging. Regards




Well, it really doesn't affect either.

--Collimation "shift" only becomes a problem if you haven't done it correctly.

--Focus shift is minimal in modern scopes and is really only (maybe) a problem for high power planetary imagers. For them, there is the Crayford.

--Never seen a focuser "shift" unless there was something badly wrong with the scope--like the owner slathering grease on the baffle tube.

--Cooling doesn't "shift." An SCT may take a while to cool, but there are easy ways to get around that.

--The correctors neither shift nor bend when using Hyperstar.

--Solidity is a function of the mount, not whether you are using an SCT. In fact, mount for mount, an SCT with its short tube is usually MORE solid on any mount.

Other than these things, though, you are 100% correct.


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shawnhar
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6225246 - 11/30/13 01:50 PM

Well for me it was about money and I assume it is for most people. I wanted a 10" scope, I read that's where the magic starts to happen.
My used 10" SCT tube costs about 500 bucks, that's the same price as an 80mm APO. No one can tell me they are going to see the spiral arms in M51 with an 80mm scope. I do love the fov in an 80mm refractor but I also like filling the fov with M13 in my 10" SCT and resolving stars to the core.
My 10" dob is great and the view is brighter and wider, but of course, it's F4.5. The stars absolutely suck at the outer 20% though, and the cost to fix that dam near is what I paid for the SCT. I also have to carefully collimate it every time I use it, not so with the SCT.
There is no way I would consider mounting the newt on my GEM, that eyepiece would be all over the place and rotating rings would cost what I paid for the SCT.
A premium 8" APO costs about the same as a Lockwood 30" F3.7, the poor little really expensive apo would fall down hard compared to that. (But it wouldn't have diffraction spikes!) Also, maybe I am wrong, but that 20 thousand dollar APO would outperform my lowly 10" SCT I'm sure, but not by that much, it's not like I would look through my scope and the 8" refractor and see a 20 thousand dolar difference. (Plus the cost of the mount to hold it!) More likely I would think, WOW, that does look better, but for the price difference I could move to Chile, set my scope up in sub-arcsec seeing at one of the best sites on the planet and smoke the view of an 8" APO every night with my junky little SCT...just sayin...


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rmollise
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Re: Why do people even buy SCTs??? new [Re: ErikB]
      #6225249 - 11/30/13 01:51 PM

Quote:

Some have said that sct's "are good for imaging". Meaning planetary, which is true. However, beginners need to know that good for planetary doesn't mean good for imaging other sky objects. The reason sct's are good for planetary imaging is that a planet needs extreme magnification (provided by the unusually long focal length) and extreme resolution, which is provided by the sct's big aperture, which is hard to match with a refractor.




An SCT can be just as good for imaging DSOs than any other design, and usually better. A Newtonian is harder to balance and mount, and a refractor lacks aperture, which is also important unless all you want is wide field.


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JJK
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Re: Why do people even buy SCTs??? new [Re: shawnhar]
      #6225318 - 11/30/13 02:32 PM

Quote:

Well for me it was about money and I assume it is for most people. I wanted a 10" scope, I read that's where the magic starts to happen.
My used 10" SCT tube costs about 500 bucks, that's the same price as an 80mm APO. No one can tell me they are going to see the spiral arms in M51 with an 80mm scope. I do love the fov in an 80mm refractor but I also like filling the fov with M13 in my 10" SCT and resolving stars to the core.
My 10" dob is great and the view is brighter and wider, but of course, it's F4.5. The stars absolutely suck at the outer 20% though, and the cost to fix that dam near is what I paid for the SCT. I also have to carefully collimate it every time I use it, not so with the SCT.
There is no way I would consider mounting the newt on my GEM, that eyepiece would be all over the place and rotating rings would cost what I paid for the SCT.
A premium 8" APO costs about the same as a Lockwood 30" F3.7, the poor little really expensive apo would fall down hard compared to that. (But it wouldn't have diffraction spikes!) Also, maybe I am wrong, but that 20 thousand dollar APO would outperform my lowly 10" SCT I'm sure, but not by that much, it's not like I would look through my scope and the 8" refractor and see a 20 thousand dolar difference. (Plus the cost of the mount to hold it!) More likely I would think, WOW, that does look better, but for the price difference I could move to Chile, set my scope up in sub-arcsec seeing at one of the best sites on the planet and smoke the view of an 8" APO every night with my junky little SCT...just sayin...




There's no doubt that commercial SCTs are a great value, and there's absolutely no need for anyone of us to justify any of your equipment. If something low-cost or high-end works for us, that's great.

However, when I was in the market for a 11"-class instrument for high resolution visual work, I wasn't concerned about the cost, I just wanted the best instrument I could handle by myself and make good use of. Regrettably, the C-11s I checked out a decade ago simply weren't up to the task. I'm pretty good at math and statistics (the thought of critically testing 100 SCTs wasn't appealing) so I decided to look elsewhere.

My particular needs at that time may have differed from yours or someone else's. That's obviously fine. I think we're all pretty fortunate that we have a decent number of relatively small companies willing to make a wide range of equipment that almost satisfies our spirit for this hobby.

Your premise about viewing in Chile is a bit more extreme than buying a high quality apo. In the latter case, you can enjoy your "investment" every clear night, and sell it when your eyes go South, as they eventually will. It's highly unlikely that many of us will quit our jobs and move to a remote mountain top in Chile. That said, I've given some thought to moving to Crete.


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JJK
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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6225322 - 11/30/13 02:34 PM

Quote:

Quote:

Quote:

I won't go into the details concerning the three 8" refractors I have built. That's not the reason for this thread. I will say that the lenses were tested before I built scopes around them though.

Scopejunkie




The answers would obviously help frame your earlier comment, but if you don't want to share them, that's your choice. Frankly, I think it's interesting to hear the lengths that some folks go through to build their own equipment. I wish I had the time to learn how to properly grind, polish, test, and coat refracting lenses with my own hands.

To my original point, I doubt a 9.25" (Celestron or Meade) SCT would outperform even a top-notch 7" apochromatic refractor (e.g., made by a company in the league of Astro-Physics or Zeiss). And that wouldn't stop me from considering one for purchase. However, I did not buy any 11" SCT I tested about a decade ago, because none of them performed well enough for the intended purpose (critical high magnification visual work). At that time, I didn't have interest in retrofitting them to see if it was a thermal issue.

In 1999, I critically tested Roland Christen's 8" and 10" Mak-Cass prototypes in very good seeing against his 180 mm and 200 mm class refractors (one was Sue & Alan French's scope that is a Moon killer). The test target was Saturn. The 8" Mak-Cass delivered images on par with the 7" apos, and the 10" just edged out the 8" refractor, but not by much. Given the compact nature of the Mak-Cass, I ordered a 10" varietal, and received it a few years later. When the seeing is good, that scope is stunning (it had better be for the list price of $10K), and I've never seen even an 11" SCT come anywhere close to this instrument's capability. I often use the Mak-Cass at 1000x to see the central star in the Ring Nebula, something I have not been able to accomplish with any 11" SCT. Roland's 10" Mak-Cass doesn't defy the laws of physics. When I want to hunt down very faint galaxies, I use a 25" Dob-Newt.

All that said, I don't expect a far lower cost SCT to perform at the same level of a much more expensive scope. However, I would like it to perform better than the ones I tested long ago. I'm in the market for one (or two).




I didn't want to go into details because they were not needed. I'm not saying that all C-9's are as good as the one I have. Most SCT's are good but not exceptional. Every now and then you can get your hands on one that is on the "high end" in optical performance. I have owned a few.

With the right mods they can be made into excellent high power instruments. My point is: You don't have to mortgage your home to get top level high resolution performance.

I used to hate SCT's with a passion until I looked into why, with many of them, their performance was lacking. I discovered a lot of things that can make them bad. Some belong to the makers and some belong to the end user. How many times have Newtonians been compared to refractors over the years with many stating that refractors are superior?

My posts are for the tinkerers who lack the funds for high end iron and give them an alternative to costly apos and high end maks.

I have read here complaints against C-11's. That is strange to me since I have had some really good ones (and a few dogs). Just lucky I guess. The pic shows one that I put a lot of time into and should have never sold.

I enjoy the challenge of making them work well.

Scopejunkie




If you're willing to describe how you built your refractors via PM, as Spock shoud have said, I'm all ears.


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ATM57
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6225343 - 11/30/13 02:47 PM Attachment (13 downloads)

Quote:

Quote:

Quote:

Quote:

I won't go into the details concerning the three 8" refractors I have built. That's not the reason for this thread. I will say that the lenses were tested before I built scopes around them though.

Scopejunkie




The answers would obviously help frame your earlier comment, but if you don't want to share them, that's your choice. Frankly, I think it's interesting to hear the lengths that some folks go through to build their own equipment. I wish I had the time to learn how to properly grind, polish, test, and coat refracting lenses with my own hands.

To my original point, I doubt a 9.25" (Celestron or Meade) SCT would outperform even a top-notch 7" apochromatic refractor (e.g., made by a company in the league of Astro-Physics or Zeiss). And that wouldn't stop me from considering one for purchase. However, I did not buy any 11" SCT I tested about a decade ago, because none of them performed well enough for the intended purpose (critical high magnification visual work). At that time, I didn't have interest in retrofitting them to see if it was a thermal issue.

In 1999, I critically tested Roland Christen's 8" and 10" Mak-Cass prototypes in very good seeing against his 180 mm and 200 mm class refractors (one was Sue & Alan French's scope that is a Moon killer). The test target was Saturn. The 8" Mak-Cass delivered images on par with the 7" apos, and the 10" just edged out the 8" refractor, but not by much. Given the compact nature of the Mak-Cass, I ordered a 10" varietal, and received it a few years later. When the seeing is good, that scope is stunning (it had better be for the list price of $10K), and I've never seen even an 11" SCT come anywhere close to this instrument's capability. I often use the Mak-Cass at 1000x to see the central star in the Ring Nebula, something I have not been able to accomplish with any 11" SCT. Roland's 10" Mak-Cass doesn't defy the laws of physics. When I want to hunt down very faint galaxies, I use a 25" Dob-Newt.

All that said, I don't expect a far lower cost SCT to perform at the same level of a much more expensive scope. However, I would like it to perform better than the ones I tested long ago. I'm in the market for one (or two).




I didn't want to go into details because they were not needed. I'm not saying that all C-9's are as good as the one I have. Most SCT's are good but not exceptional. Every now and then you can get your hands on one that is on the "high end" in optical performance. I have owned a few.

With the right mods they can be made into excellent high power instruments. My point is: You don't have to mortgage your home to get top level high resolution performance.

I used to hate SCT's with a passion until I looked into why, with many of them, their performance was lacking. I discovered a lot of things that can make them bad. Some belong to the makers and some belong to the end user. How many times have Newtonians been compared to refractors over the years with many stating that refractors are superior?

My posts are for the tinkerers who lack the funds for high end iron and give them an alternative to costly apos and high end maks.

I have read here complaints against C-11's. That is strange to me since I have had some really good ones (and a few dogs). Just lucky I guess. The pic shows one that I put a lot of time into and should have never sold.

I enjoy the challenge of making them work well.

Scopejunkie




If you're willing to describe how you built your refractors via PM, as Spock shoud have said, I'm all ears.




Which one are you interested in, the single tube, split tube or Rail Scope? They all used lenses from China (Po' Boy refractors)

BTW, the cooled C-11 in the previous picture was traded for my first 8" lens. I thought I was building my dream scope. An 8" F/12 refractor is a lot to live with when you have to set it up each night.

Scopejunkie


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6225362 - 11/30/13 02:57 PM

Quote:

Quote:

Some have said that sct's "are good for imaging". Meaning planetary, which is true. However, beginners need to know that good for planetary doesn't mean good for imaging other sky objects. The reason sct's are good for planetary imaging is that a planet needs extreme magnification (provided by the unusually long focal length) and extreme resolution, which is provided by the sct's big aperture, which is hard to match with a refractor.




An SCT can be just as good for imaging DSOs than any other design, and usually better. A Newtonian is harder to balance and mount, and a refractor lacks aperture, which is also important unless all you want is wide field.




Rod, how are you defining "better" here?

From what I've experienced and seen, SCTs are interesting and flexible imaging platforms (long to short focal lengths in one instrument with relatively small additional investments).

That said, I was fortunate to find a used Ceravolo 300 Astrograph (f/4.9 & f/9) that has none of the issues associated with lower-cost SCTs. I don't have a lot of imaging time logged on this scope (the weather has been extremely uncooperative for the last few years), but the COS 300 seems lke an ideal instrument (easy to collimate, good resolution, fixed primary, compact, great thermal response, rugged, etc.). Regrettably, Peter stopped making them for now.

While rebuilding SCTs might be fun for some, and a significant cash-saving process, I don't enjoy that process. I used to, but other stuff started consuming a lot of my time about 20 years ago.


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orion61

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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6225380 - 11/30/13 03:07 PM

I love watching people..
We are just..
If you want the most ease of use, Transportation, the best OVER ALL performance for the money, buy a Schmidt.
If you want the most light grasp,for the $ buy a...
If you want to spend your Childrens College fund for slightly better performance, buy a....
there is no changing of ones mind! I have or Have had one of each type, I CHOOSE my Schmidts as MY favorite.
If money meant nothing, and had a Dump truck of it, I'd own a Mountain home with a 30" Refractor housed in an Observatory. Right next to my 100" Schmidt!
I'll see you all at the Star Party where well all be enjoying the Skys..
see what you started Eddy....


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: orion61]
      #6225393 - 11/30/13 03:15 PM

If you want to see what a cheap scope can do with a little work, I just posted test images here...

Before & After Test Shots


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rmollise
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6225397 - 11/30/13 03:18 PM

Quote:



Rod, how are you defining "better" here?






Easier to use for imaging and capable of delivering results as good or better than any other design as attested to by over 40 years of outstanding SCT pictures.


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A6Q6
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6225399 - 11/30/13 03:19 PM

I can see a C11 or C14 in my future. After having a very good 6" Mak Cass for 35 years, I found an old orange tube C5 in a pawn shop. It has no “image” or “mirror” shift like I have seen, even in some Questars. My Mak doesn't have any ether. But what really got me about the C5 was the sharpness of the image. I had never seen that in a SCT,and the portability is unbelievable. I hate to say It, but I would take that little C5 over the RV6 that I once had and that scope you could set next to anything. So for me that's why "people even buy SCTs???" even if its an optical gamble.

Edited by A6Q6 (11/30/13 03:26 PM)


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drago
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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6225409 - 11/30/13 03:27 PM

i hear, Anatoliy Sankovich, a word famous Santel MCT maksutov scopes maker once says: "who understand, choose newtonian..."

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ErikB
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6225414 - 11/30/13 03:30 PM

Quote:

An SCT can be just as good for imaging DSOs than any other design, and usually better. A Newtonian is harder to balance and mount, and a refractor lacks aperture, which is also important unless all you want is wide field.




While it is true that an sct is easier than a newt for the mount to handle, all to often the beginner might fall into the trap of thinking the mount portion of a forked sct is of suitable quality for imaging faint objects. (Ask me how I know.) In fact I believe that for the smaller sct sizes, likely to be someone's first scope, the amount of money sunk into the design by the manufacturer for the mount portion of a forked sct is less than would be appropriate for imaging of faint objects requiring multiminute exposures at the focal length of the sct. That is of course a generalization that isn't going to be true for every case, but with a majority of new users being visual, how could it, in general, be any different? So, yes for given scope spec's, an sct is easier on the mount with respect to stability, but that means little if the beginner planning dso imaging finds that the fork drive is of insufficient quality for successful guiding. And, yes, if high magnification is desired, an sct variety may be the ticket, but the beginner may all too easily make the mistake of thinking an 8" sct will guide well with its standard fork or with a cheap GEM. Besides those issues, I believe the average standard sct (I only have experience with two 8"s and one 9.25") creates more bloated star images than good newts or refractors, even at the center, for the same aperture and magnification. This of course is another aspect of how contrast varies with the scale of object detail, but it definitely has a negative impact on both imaging and visual use.


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drago
sage


Reged: 01/11/08

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Re: Why do people even buy SCTs??? new [Re: A6Q6]
      #6225419 - 11/30/13 03:33 PM

Quote:

But what really got me about the C5 was the sharpness of the image. I had never seen that in a SCT,and the portability is unbelievable. I hate to say It, but I would take that little C5 over the RV6 that I once had and that scope you could set next to anything. So for me that's why "people even buy SCTs???" even if its an optical gamble.




as i understand, people buy SCT for that, SCT sometimes got a sharp image. not a near as sharp, as in normal APO, but a bit more sharp than a absolute messy image...?


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rmollise
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6225429 - 11/30/13 03:37 PM

Quote:

i hear, Anatoliy Sankovich, a word famous Santel MCT maksutov scopes maker once says: "who understand, choose newtonian..."




All things being equal, perhaps...but no matter what Antoiliy says, all things are rarely equal.


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rmollise
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Re: Why do people even buy SCTs??? new [Re: ErikB]
      #6225431 - 11/30/13 03:39 PM

Quote:



While it is true that an sct is easier than a newt for the mount to handle, all to often the beginner might fall into the trap of thinking the mount portion of a forked sct




Perhaps, though countless good pictures have been done with forks. AND you can put your C8 on a dadgum AP1600 if the spirit moves you.


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orion61

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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6225440 - 11/30/13 03:46 PM

Rod, Mark twain once said...
"Never get into an argument with an idiot, He will bring you down to his level and beat you with experience"?
To each their own.. You cant prove Memories, or opinions.
This one is going South.. I'm happy with my Schmidt, I wonder why people try so hard to convince me, my opinion of my equipment is wrong, when I have had all the different types of scopes, and I'm so happy with what I have, and the results I have achieved from it????


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David PavlichAdministrator
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6225460 - 11/30/13 04:05 PM

[quote
All that said, I don't expect a far lower cost SCT to perform at the same level of a much more expensive scope. However, I would like it to perform better than the ones I tested long ago. I'm in the market for one (or two).




I'm all for giving props when deserved. So many times, we have off the shelf SCs compared to what are essentially hand made refractors or high end Newts that cost much more than the SC. John has stated above what few ever do when making this type comparison. Thanks, John!

David


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: David Pavlich]
      #6225478 - 11/30/13 04:14 PM

I have an 8 inch SCT that the only reason I would trade it even for a top of the line 6 inch APO, would be so I could sell it and get another 8 inch SCT and pocket the rest!

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Geo31
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Re: Why do people even buy SCTs??? new [Re: orion61]
      #6225617 - 11/30/13 05:40 PM

Quote:

I love watching people..
We are just..




Boy howdy (obscure southern expression that essentially means: I couldn't agree more)


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: orion61]
      #6225653 - 11/30/13 06:05 PM

Quote:


To each their own.. You cant prove Memories, or opinions.
This one is going South.. I'm happy with my Schmidt, I wonder why people try so hard to convince me, my opinion of my equipment is wrong, when I have had all the different types of scopes, and I'm so happy with what I have, and the results I have achieved from it????




I don't recall anyone here suggesting you have, or anyone else has, the wrong equipment. I'm not even sure what that statement would mean.

From your signature line, and what I'd like to do in the future, you seem to have good stuff. I have enough scopes and mounts for my own personal use, but I'm thinking about setting up an observatory for public use in a mountain community. A C-14 could be a good compromise, in the sense that while it can't provide as deep a view at the EP that a 32" Dob-Newt can, it can certainly show very nice views of a lot of DSOs, and striking images of fainter ones if a CCD camera is used as an electronic eyepiece (and th C-14 is pretty compact).

Edited by JJK (11/30/13 06:06 PM)


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kkokkolisModerator
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6225722 - 11/30/13 06:56 PM

Hey people, this is the Cats and Casses field. Whoever loves mostly Newtonians and Refractors can visit their specialized subforums! It seems simple to me.

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Re: Why do people even buy SCTs??? new [Re: kkokkolis]
      #6226028 - 11/30/13 10:10 PM

As far as imaging goes... as with visual, my experience has been that an SCT makes a fine general purpose platform, particularly when paired with a modern DSLR or large format (APS-C) CCD. I usually leave mine at its native f/10 for deepsky imaging, though I'll occassionally pull it in to f/6.3. For planetary I'll stretch it out to f/30. The long focal length made imaging with small chip CCDs a challenge, but that's not the problem that it once was with the advent of affordable DSLRs and their modern CCD cousins.

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Re: Why do people even buy SCTs??? new [Re: ErikB]
      #6226052 - 11/30/13 10:27 PM

Quote:

Quote:

An SCT can be just as good for imaging DSOs than any other design, and usually better. A Newtonian is harder to balance and mount, and a refractor lacks aperture, which is also important unless all you want is wide field.




While it is true that an sct is easier than a newt for the mount to handle, all to often the beginner might fall into the trap of thinking the mount portion of a forked sct is of suitable quality for imaging faint objects. (Ask me how I know.) In fact I believe that for the smaller sct sizes, likely to be someone's first scope, the amount of money sunk into the design by the manufacturer for the mount portion of a forked sct is less than would be appropriate for imaging of faint objects requiring multiminute exposures at the focal length of the sct. That is of course a generalization that isn't going to be true for every case, but with a majority of new users being visual, how could it, in general, be any different? So, yes for given scope spec's, an sct is easier on the mount with respect to stability, but that means little if the beginner planning dso imaging finds that the fork drive is of insufficient quality for successful guiding. And, yes, if high magnification is desired, an sct variety may be the ticket, but the beginner may all too easily make the mistake of thinking an 8" sct will guide well with its standard fork or with a cheap GEM. Besides those issues, I believe the average standard sct (I only have experience with two 8"s and one 9.25") creates more bloated star images than good newts or refractors, even at the center, for the same aperture and magnification. This of course is another aspect of how contrast varies with the scale of object detail, but it definitely has a negative impact on both imaging and visual use.




Some people seem to confuse the term "SCT" with "fork mount." We are not talking about mounts here at all. Mounts are a whole other issue. We are only talking about optical tube assemblies without regard to what kind of mount you want to have it on, GEM, fork or other. A fork mount is not the "standard" mount for all SCTs, particularly for astrophotography, and there are only a couple of "fork" mounts that are designed to really handle SCTs for astrophotography but still allow the SCT to be removed and used on other mounts.

Not speaking to anyone in particular, but when it comes down to it, some people will always think that their favorite scope type is better than one of the other scope types and some even feel the need to put down the other types. The rest of us understand that every scope type is a compromise of one sort or another and each type has their value without being somehow degraded by comparison to another type of scope. I love CATs, I love refractors and can even love Newts (although I have little interest in owning another one at this time). In addition, there are variants of those three types like the MakNewt, DK, etc. that are wonderful scopes as well for certain purposes. Those that choose to strongly put down one or another type if scope are often over invested (monetarily or mentally) in the particular type of scope they own and may never be able to admit the value of one of the other types even if everyone else could see it provide better results.


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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226327 - 12/01/13 02:27 AM

drago said: "but a bit more sharp than a absolute messy image...?" Sharp is Sharp, not a little bit or almost. If you haven't experienced what a good SCT can do you don't know what your missing. I would not keep my C5 if it wasn't capable of producing a really sharp image.

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drago
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Re: Why do people even buy SCTs??? new [Re: A6Q6]
      #6226343 - 12/01/13 02:58 AM

Quote:

drago said: "but a bit more sharp than a absolute messy image...?" Sharp is Sharp, not a little bit or almost. If you haven't experienced what a good SCT can do you don't know what your missing. I would not keep my C5 if it wasn't capable of producing a really sharp image.




maybe i wrong, in that case please say, but:
image sharpness in large degree is affected by central obstruction? bigger is CO, softer image.
Also resolution is affected by CO.
the larger is CO, the worster is image.as i understand, most SCT have obstruction larger than 30 percent?
CO is a really evil, and that become undetectable only if it less than 16 percent by diameter. and that is only about CO there. we do not speak about machine-polished rough corrector plate, who also do not add benefits, and maybe about 3rd spherical aberration - dont know, it is a SCT satellite, or not? in MCT it is impossible to avoid SA, as i hear.


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A6Q6
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226660 - 12/01/13 10:23 AM

drago said:"dont know, it is a SCT satellite, or not? in MCT it is impossible to avoid SA, as i hear" Seeing is believing, so you have to go to a star party on a night of good seeing and actually look through good examples of these two optical designs. It really really will make a believer out of you.

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Cotts
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226683 - 12/01/13 10:35 AM

The CO's typical in an SCT are not so large that it has any affect at all at prime focus where the entire diffraction pattern is only a pixel or two wide.

Even for high resolution imaging the CO of an SCT does not reduce contrast to any ruinous degree or else images like these would not be possible.

CO's of 25-35% by diameter do have an effect on high magnification visual viewing of planets and the moon in scopes up to 8" in size when compared to same-sized (or slightly smaller) unobstructed scopes.

Once you get into 9" and larger scopes the central obstruction is a given in virtually every scope owned by amateurs - unless you know of some people with 9" or larger refractors in their backyards. From about 9" and up aperture and lens/mirror quality are pretty much the only variables worth considering.

I sometimes grow weary of the "CO is a disaster" way of thinking. As in so many debates here on CN, the truth is "it depends."

Dave


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Re: Why do people even buy SCTs??? new [Re: A6Q6]
      #6226691 - 12/01/13 10:38 AM

Was their a point to this whole thread? Every design has a compromise built in. Know your scopes, buy what you deem to be the best compromise to you for the application you'll use it in.

Move on and don't worry when someone spends time modding their scope. You can do it too if you want. If you never saw a difference after mods and someone else does, so what. No need to bake your noodle over it.

Enjoy your compromised scope whether its a big or small SCT, MCT, Apo, Dob, RC, Achro, or (name anything else because it all applies).



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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: Cotts]
      #6226695 - 12/01/13 10:40 AM

+1

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drago
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Re: Why do people even buy SCTs??? new [Re: A6Q6]
      #6226697 - 12/01/13 10:41 AM

i'd read a professional optical system designers things about MCT design. they said, in that design cannot be avoid of higher orders SA.
I personally never have an SCT or MCT. One time i thinking about get in my paws a 127 Synta's MCT for megaportable lunar instrument, and also be a test cats with my own experience, but i go reading, concearning, and got to a conclusion, on a planets i not win anything in comparing to 100ed, and on DSO it also be a questionable. i add this to very long thermostabilization times ( in winter there may be a delta with room temperature, to outdoors as 40 or bit more, degrees of kelvin), and stay at me 100ed, with next goal to a larger newtonian dob, who i realised in last months

P.S. about a CA: in a start of my telescopes owning i have a two scopes: a bresser 60 \ 800 achro and a "bresser pluto" - 114 / 500 scope, whose real aperture be around of 85 - 90 mm, and central obstruction is close to 40 or so, percents.
i be compare these two on moon and jupiter, and the difference on jupiter was a very terribly. on moon these newtonian looks better than achro, this is a very contrasty objects. but on jupiter is be very hard to see a cloud strips on planet discs. on a smaller achro it is impossible to miss that strips. that's my experience about CA importancy in visual observations.

Edited by drago (12/01/13 10:47 AM)


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Re: Why do people even buy SCTs??? new [Re: Vondragonnoggin]
      #6226731 - 12/01/13 10:54 AM

Quote:

Was their a point to this whole thread?





Sure, it was a perfect opportunity for a few friends to get together over the Thanksgiving weekend (at least in the USA) and enjoy a lively discussion involving something very dear to their hearts...

Cheers, Bill


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drago
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Re: Why do people even buy SCTs??? new [Re: Vondragonnoggin]
      #6226751 - 12/01/13 11:04 AM

Quote:

Was their a point to this whole thread? Every design has a compromise built in.




cannot imagine, what compromise is in an apo? :-O


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Footbag
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226754 - 12/01/13 11:06 AM

Quote:

Quote:

Was their a point to this whole thread? Every design has a compromise built in.




cannot imagine, what compromise is in an apo? :-O




Price!


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Vondragonnoggin
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226756 - 12/01/13 11:08 AM

Quote:

Quote:

Was their a point to this whole thread? Every design has a compromise built in.




cannot imagine, what compromise is in an apo? :-O




Size constraints. Mounting requirements, portability when using larger sizes. Cost prohibitive for a good majority. Doesn't have to be an optical compromise to be a compromise.


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rmollise
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226772 - 12/01/13 11:16 AM

Quote:

Quote:

Was their a point to this whole thread? Every design has a compromise built in.




cannot imagine, what compromise is in an apo? :-O





Start with small aperture.


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drago
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Re: Why do people even buy SCTs??? new [Re: Vondragonnoggin]
      #6226774 - 12/01/13 11:17 AM

on that view all is compromise. i want an 2 metres of aperture with 1 kilogramm weight, and with compactness no larger than a 10x50 binoculars.
it is like to a demagogy. price also not a optical system compromise. i think, refractors is most perfect optical scheme. second will be newtonians, especially in designs without CO....
but ok, be a happy what your have. some folks were beware of looks in another optical systems, because all is relative, and can be perceived in comparison - if you never see and sit in ferrary, you can think, a vw passat VR6 is "very good,fast and sporty car"...:D


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Vondragonnoggin
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226778 - 12/01/13 11:20 AM

Quote:

on that view all is compromise. i want an 2 metres of aperture with 1 kilogramm weight, and with compactness no larger than a 10x50 binoculars.
it is like to a demagogy. price also not a optical system compromise. i think, refractors is most perfect optical scheme. second will be newtonians, especially in designs without CO....
but ok, be a happy what your have. some folks were beware of looks in another optical systems, because all is relative, and can be perceived in comparison - if you never see and sit in ferrary, you can think, a vw passat VR6 is "very good,fast and sporty car"...:D




I'm sure many are happy with their Ferrari's even if remote control size!


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drago
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Re: Why do people even buy SCTs??? new [Re: Vondragonnoggin]
      #6226794 - 12/01/13 11:27 AM


for small sizes rules refractors, for big - newtodobs
if the climate is stable, and temperature forever is about a 17 - 25 celsium, then i think, CATs may be more or less usable instrument. in our climate is only one way in this - cut a big holes in that OTA, and put ventilators there. as so,as in newtonians, but there sometimes is ok with ventilaors to rear side of mirror cell.


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rmollise
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226899 - 12/01/13 12:10 PM

Quote:

on that view all is compromise.




No it's not. With 8-inches of aperture, you can see a lot of deep sky objects and details in may of them. In a 3 or 4-inch APO? Not so much. You can't defeat the laws of physics by throwing money at them.


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EFT
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226913 - 12/01/13 12:15 PM

It takes surprisingly little ventilation to thermally stabilize an SCT. You really need to get out and try one so that you can see how well they do. Just make sure it is well collimated. Going off the theoretical analysis and the on-line arguments is never going to be the way to judge an optical design.

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mmalik
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6226924 - 12/01/13 12:22 PM

Quote:

Solidity is a function of the mount, not whether you are using an SCT. In fact, mount for mount, an SCT with its short tube is usually MORE solid on any mount.




Missing the point Rod; I am referring to inherent fluidity of SCT design where all is shifting at times. SCTs just haven't reached that 'set-it and forget-it' solid-state quality over the years, and I understand cost is a factor but that's not to say such "shifty..." issues are not there. Regards


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drago
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6226928 - 12/01/13 12:23 PM

Quote:

Quote:

on that view all is compromise.




No it's not. With 8-inches of aperture, you can see a lot of deep sky objects and details in may of them. In a 3 or 4-inch APO? Not so much. You can't defeat the laws of physics by throwing money at them.




O'Meara look in 4" apo, btw
on beside this -i do not see a big difference in portability and weight compare 8" sct and 8" dob. dob is more compact ( if we account mount too), have less light loss, faster thermostab, and less price...:)


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Re: Why do people even buy SCTs??? new [Re: drago]
      #6226983 - 12/01/13 12:45 PM

Quote:

on that view all is compromise. i want an 2 metres of aperture with 1 kilogramm weight, and with compactness no larger than a 10x50 binoculars.
it is like to a demagogy. price also not a optical system compromise. i think, refractors is most perfect optical scheme. second will be newtonians, especially in designs without CO....
but ok, be a happy what your have. some folks were beware of looks in another optical systems, because all is relative, and can be perceived in comparison - if you never see and sit in ferrary, you can think, a vw passat VR6 is "very good,fast and sporty car"...:D




Again, unless use are very religious, I don't understand how a optical system that superimposes the sign of the cross on every bright star can be considered a perfect optical system. I think what you really state is just your opinion.


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drago
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Re: Why do people even buy SCTs??? new [Re: Wmacky]
      #6227031 - 12/01/13 01:04 PM

refractors not have crosses inducted by secondary support.
newtonians not perfect, but in that direction - newtonians without central obstruction too not have a crosses, and on traditional newtonians you have use a curved vanes, and also not have a cross.


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A6Q6
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Re: Why do people even buy SCTs??? new [Re: Vondragonnoggin]
      #6227110 - 12/01/13 01:44 PM

Vondragonnoggin said: "Was their a point to this whole thread?...Know your scopes," a lot of us sit here in the "Land of Plenty" and forget there are people who have only read about different designs and haven't had a chance to look through them. I'm sure Eddgie started this thread on a humbrum day just for fun, but a lot of good can come from a thread like this because of the info that is shared here on CN. And yes I'm still enjoying my Thanksgiving leftovers

Edited by A6Q6 (12/01/13 01:47 PM)


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A6Q6
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6227194 - 12/01/13 02:11 PM

drago said: "O'Meara look in 4" apo, btw" I will also add Rodger W Gordon: 3.5" Questar. These people have eyes that most of us mortals don't have. Individual eyesight is a topic that really needs to be covered .

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rmollise
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Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6227204 - 12/01/13 02:15 PM

Quote:



Missing the point Rod; I am referring to inherent fluidity of SCT design where all is shifting at times. SCTs just haven't reached that 'set-it and forget-it' solid-state quality over the years, and I understand cost is a factor but that's not to say such "shifty..." issues are not there. Regards




I get the point. I just disagree with you.


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Dwight J
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Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6227303 - 12/01/13 03:13 PM

I collimated my old C8 twice in the 25 yrs. I owned it. And it was not pampered by never leaving home. It was packed up and moved three times a week and often on not nice roads. Pretty stable in my book. It was on a fork mount with a Byers drive and I took many astro photos with it not noticing how inherently unstable it was supposed to be. I wonder about all the hoopla about cool down time - it must be climate related b/c I have not had an issue with it. I know one club that sold their 7" AP apo refractor because all that glass would not cool down even giving it all night.
I don't relish laying on the ground to view the zenith and having to rais the tripod all the way up just for that privilege. I equally dislike climbing a ladder and having to bring one along. Moving my big dobs required a truck, dolly, and two guys.
Easy to critcize SCT's, everyone's whipping boy, by minimizing or glossing over the shortcomings of other designs. Sure, it would be nice to have a scope of every design to fulfill every need but a SCT offers the closest to meeting all those needs with one design. An overlooked quality that other designs often lack is backfocus, a serious issue with Newts.

Edited by Dwight J (12/01/13 03:46 PM)


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mmalik
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Re: Why do people even buy SCTs??? new [Re: Dwight J]
      #6227354 - 12/01/13 03:43 PM

What gets lost in translation is visual vs. photographic performance. SCTs may be 'ok' for visual but it is a proven fact that they have lagged behind times in AP. An example here... (I hope OP wouldn't mind quoting him?) Regards

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ATM57
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Re: Why do people even buy SCTs??? new [Re: Cotts]
      #6227362 - 12/01/13 03:46 PM

Quote:

Even for high resolution imaging the CO of an SCT does not reduce contrast to any ruinous degree or else images like these would not be possible.

CO's of 25-35% by diameter do have an effect on high magnification visual viewing of planets and the moon in scopes up to 8" in size when compared to same-sized (or slightly smaller) unobstructed scopes.

Once you get into 9" and larger scopes the central obstruction is a given in virtually every scope owned by amateurs - unless you know of some people with 9" or larger refractors in their backyards. From about 9" and up aperture and lens/mirror quality are pretty much the only variables worth considering.

I sometimes grow weary of the "CO is a disaster" way of thinking. As in so many debates here on CN, the truth is "it depends."

Dave




Excellent! Your statements are very true and I base this on almost 40 years of visual observation. Once you get past 8" the secondary obstruction becomes much less of an issue than it is exaggerated to be. Overall optical correction and temperature control are much more important. Even my 8" refractors had to temp equalize for their best performance.

Many are of the misunderstanding that "if it's obstructed then it is automatically inferior to my unobstructed instrument". As you have stated "it depends"

After 8" of aperture I find these points to be the most important regardless of design:

1. Optical design produced as close as possible to the design specification.
2. Excellent overall optical correction (final wavefront)
3. Smooth optical surfaces (very important)
4. Temperature control.
5. Good mechanical support.
6. Secondary obstruction. (Has an effect but seeing is normally the limiting factor as to what is seen through the eyepiece when you reach this size level. Reducing the obstruction reduces the instrument's sensitivity to seeing conditions)

I believe that a telescope that accomplishes these items will be an excellent performer.

I know some will disagree with this but it is based on decades of visual telescope use and experimentation and I'm sticking with it

Scopejunkie


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6227365 - 12/01/13 03:49 PM

@ Dwight J

Very good post and acurate.


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MikeML
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Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6227391 - 12/01/13 04:06 PM

Quote:

What gets lost in translation is visual vs. photographic performance. SCTs may be 'ok' for visual but it is a proven fact that they have lagged behind times in AP. An example here... (I hope OP wouldn't mind quoting him?) Regards




That may be true for the stock SCTs with the ubiquitous 6.3 reducer, but there are other reducers available and a new generation of SCTs.


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: MikeML]
      #6227406 - 12/01/13 04:17 PM

I am more than happy with the images from mine, they are sharp, detailed and all shot in Alt/Az in a small amount of time.

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Footbag
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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6227459 - 12/01/13 04:42 PM

I love imaging with an SCT. Sure, it's a bit slow, but there's nothing like having that reach for small galaxies or planetary nebula.

Yes. The long FL is hard to control and an SCT isn't suggested for beginners; but that doesn't mean it doesn't perform when operating on a sufficient mount.

The Edge, though, really is amazing. Perfect stars throughout the field. For long FL imaging, you cannot beat the price performance.


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Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6227463 - 12/01/13 04:44 PM

Quote:

What gets lost in translation is visual vs. photographic performance. SCTs may be 'ok' for visual but it is a proven fact that they have lagged behind times in AP. An example here... (I hope OP wouldn't mind quoting him?) Regards




"Proven?" Maybe for you.


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kansas skies
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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6227468 - 12/01/13 04:45 PM

Quote:

Quote:

Even for high resolution imaging the CO of an SCT does not reduce contrast to any ruinous degree or else images like these would not be possible.

CO's of 25-35% by diameter do have an effect on high magnification visual viewing of planets and the moon in scopes up to 8" in size when compared to same-sized (or slightly smaller) unobstructed scopes.

Once you get into 9" and larger scopes the central obstruction is a given in virtually every scope owned by amateurs - unless you know of some people with 9" or larger refractors in their backyards. From about 9" and up aperture and lens/mirror quality are pretty much the only variables worth considering.

I sometimes grow weary of the "CO is a disaster" way of thinking. As in so many debates here on CN, the truth is "it depends."

Dave




Excellent! Your statements are very true and I base this on almost 40 years of visual observation. Once you get past 8" the secondary obstruction becomes much less of an issue than it is exaggerated to be. Overall optical correction and temperature control are much more important. Even my 8" refractors had to temp equalize for their best performance.

Many are of the misunderstanding that "if it's obstructed then it is automatically inferior to my unobstructed instrument". As you have stated "it depends"

After 8" of aperture I find these points to be the most important regardless of design:

1. Optical design produced as close as possible to the design specification.
2. Excellent overall optical correction (final wavefront)
3. Smooth optical surfaces (very important)
4. Temperature control.
5. Good mechanical support.
6. Secondary obstruction. (Has an effect but seeing is normally the limiting factor as to what is seen through the eyepiece when you reach this size level. Reducing the obstruction reduces the instrument's sensitivity to seeing conditions)

I believe that a telescope that accomplishes these items will be an excellent performer.

I know some will disagree with this but it is based on decades of visual telescope use and experimentation and I'm sticking with it

Scopejunkie




Brings to mind that half-blind Cassegrain floating around out there in space.

Bill


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: kansas skies]
      #6227511 - 12/01/13 05:06 PM

Yes and only the best images ever seen. Why doesn't someone contact them and let them know it should of been an APO or Newtonian.

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ATM57
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Re: Why do people even buy SCTs??? new [Re: kansas skies]
      #6227568 - 12/01/13 05:40 PM

Quote:

Quote:

Quote:

Even for high resolution imaging the CO of an SCT does not reduce contrast to any ruinous degree or else images like these would not be possible.

CO's of 25-35% by diameter do have an effect on high magnification visual viewing of planets and the moon in scopes up to 8" in size when compared to same-sized (or slightly smaller) unobstructed scopes.

Once you get into 9" and larger scopes the central obstruction is a given in virtually every scope owned by amateurs - unless you know of some people with 9" or larger refractors in their backyards. From about 9" and up aperture and lens/mirror quality are pretty much the only variables worth considering.

I sometimes grow weary of the "CO is a disaster" way of thinking. As in so many debates here on CN, the truth is "it depends."

Dave




Excellent! Your statements are very true and I base this on almost 40 years of visual observation. Once you get past 8" the secondary obstruction becomes much less of an issue than it is exaggerated to be. Overall optical correction and temperature control are much more important. Even my 8" refractors had to temp equalize for their best performance.

Many are of the misunderstanding that "if it's obstructed then it is automatically inferior to my unobstructed instrument". As you have stated "it depends"

After 8" of aperture I find these points to be the most important regardless of design:

1. Optical design produced as close as possible to the design specification.
2. Excellent overall optical correction (final wavefront)
3. Smooth optical surfaces (very important)
4. Temperature control.
5. Good mechanical support.
6. Secondary obstruction. (Has an effect but seeing is normally the limiting factor as to what is seen through the eyepiece when you reach this size level. Reducing the obstruction reduces the instrument's sensitivity to seeing conditions)

I believe that a telescope that accomplishes these items will be an excellent performer.

I know some will disagree with this but it is based on decades of visual telescope use and experimentation and I'm sticking with it

Scopejunkie




Brings to mind that half-blind Cassegrain floating around out there in space.

Bill




I'd like to share a real experience that I have shared elsewhere. Small telescope users please don't be offended:

I will share my own obstructed aperture eyeopener many years ago. While at a star party, a friend and I were basking in the glow of how well our refractors were showing Saturn to the attendees. My Vixen 4" F/10 and his 4" F/15 Unitron were kicking butt. A lowly Celestron 8 was near by. We lowered ourselves for a look-see at Saturn and to our pleasure, the image couldn't match our views. Enjoying our obvious telescope superiority, we continued to show the planet to any and all who wanted a view. As the evening progressed, unknown to us, the C-8 (which happened to be a good one) was coming into it's own. The owner never said a word as to the stunning view the scope was beginning to produce. After a couple of hours, to give myself another pat on the back for bringing such a good scope to the star party, I went over to the C-8 for another view. To my amazement the view was stunning. I would guess the scope was running at about 350x. The view was so nice that I had a hard time walking away. My puny 4" couldn't come close to the view the C-8 was putting up. No matter how much magnification I tried to run, I couldn't touch it. Talk about a large slice of humble pie. The owner of the C-8 never said a word but he could tell that I had just been blown away by his scope.

On this date I came to the realization that all SCT's were not bad as I had thought they were.

Scopejunkie


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Rick Woods
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Re: Why do people even buy SCTs??? new [Re: Vondragonnoggin]
      #6227616 - 12/01/13 06:00 PM

Quote:

Was their a point to this whole thread? Every design has a compromise built in. Know your scopes, buy what you deem to be the best compromise to you for the application you'll use it in.

Move on and don't worry when someone spends time modding their scope. You can do it too if you want. If you never saw a difference after mods and someone else does, so what. No need to bake your noodle over it.

Enjoy your compromised scope whether its a big or small SCT, MCT, Apo, Dob, RC, Achro, or (name anything else because it all applies).






How dare you introduce common sense into a telescope debate!


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JJK
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6227622 - 12/01/13 06:04 PM

Quote:

Quote:

Quote:

Was their a point to this whole thread? Every design has a compromise built in.




cannot imagine, what compromise is in an apo? :-O





Start with small aperture.




No need to go small with an apo.


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JJK
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6227630 - 12/01/13 06:08 PM

Quote:

Quote:

on that view all is compromise.




No it's not. With 8-inches of aperture, you can see a lot of deep sky objects and details in may of them. In a 3 or 4-inch APO? Not so much. You can't defeat the laws of physics by throwing money at them.




You can see far more with a 20" Dob, and they aren't prohibitively expensive.


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rmollise
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6227639 - 12/01/13 06:11 PM

Quote:

Quote:

Quote:

on that view all is compromise.




No it's not. With 8-inches of aperture, you can see a lot of deep sky objects and details in may of them. In a 3 or 4-inch APO? Not so much. You can't defeat the laws of physics by throwing money at them.




You can see far more with a 20" Dob, and they aren't prohibitively expensive.




But it's hard to take pictures with one. Or spectra...or... That's the thing...the SCT does many things well. And there's also no doubt that you'll see a hell of a lot more with an 8-inch as your primary scope than a freaking four.


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Itz marcus
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6227698 - 12/01/13 06:37 PM

Hi,
I didn't go for a sct because I was afraid of collimation and I also believed what was said about the co. I used my Eon 120 for he last 7 years? Man do I love he scope but I did want something bigger and I couldn't afford a six inch apo or a long focus achro (and I wanted an eight inch scope ). I finally took the plunge and bought. Used c8 at a fraction of the price of a used 120 Ed scope. Although I have to service it as the scope wouldn't hold collimation, when it was in collimation the views were amazing. Things were easier to see and I was able to see more in my light poisoned city than the 120. I hope to be able to keep the 120 but if I can't afford to keep both then it looks like the c8 will be the scope to stay and as much as I really love the Eon 120 I will reluctantly let it go.
Clear skies
Itz


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JJK
Carpal Tunnel


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Re: Why do people even buy SCTs??? new [Re: Dwight J]
      #6227738 - 12/01/13 07:04 PM

Quote:

I collimated my old C8 twice in the 25 yrs. I owned it. And it was not pampered by never leaving home. It was packed up and moved three times a week and often on not nice roads. Pretty stable in my book. It was on a fork mount with a Byers drive and I took many astro photos with it not noticing how inherently unstable it was supposed to be. I wonder about all the hoopla about cool down time - it must be climate related b/c I have not had an issue with it. I know one club that sold their 7" AP apo refractor because all that glass would not cool down even giving it all night.
I don't relish laying on the ground to view the zenith and having to rais the tripod all the way up just for that privilege. I equally dislike climbing a ladder and having to bring one along. Moving my big dobs required a truck, dolly, and two guys.
Easy to critcize SCT's, everyone's whipping boy, by minimizing or glossing over the shortcomings of other designs. Sure, it would be nice to have a scope of every design to fulfill every need but a SCT offers the closest to meeting all those needs with one design. An overlooked quality that other designs often lack is backfocus, a serious issue with Newts.




Dwight, I don't see SCTs as "everyone's whipping boy". It's a legitimate and versatile design, and has brought real time astronomy to many folks at bargain-basement prices (I think they are still a great deal).

Oddly, some here use refractors and Newtonians as their whipping boys, which is silly. Those scopes, and others, are legitimate designs, and some manfacturers have implemented them exceptionally well.

For example, AP and Zeiss apos are indeed very expensive per inch or aperture. So what? They are a pleasure to use and the ones I've played with (and still do) produce stunning lunar, solar, and planetary images. The larger ones give some much larger scopes (e.g., Tak Mewlon 300) a run for their money on some DSOs (I have both, so I have no pony in that race).

Instead of getting a C-11, I decided to buy an AP 10" f/14.6 Mak-Cass. It is a well designed instrument (great optics and thermal management), and it too provides stunning views of the Moon, planets, and brighter DSOs.

Rod, with all due respect, this scope is much better than an equivalent aperture SCT (of course, this is meaningless, because one can't get this AP scope anymore), but when I want to look at DSOs in detail, I use a much larger Dob-Newt. Of course, if one can only have one scope, then you learn to get the most out of it. For the longest time, I observed solely with an AP Traveler (105 mm f/5.9). I pushed that thing to its limit and even star hopped to find DSOs (I used to enjoy that process over the use of go-to mounts). However, if one can afford more than one scope, or have friends with different scopes, that opens up new possibilities.

To others here, ignoring the limitations of any scope design or implementation, doesn't help anyone. When I was looking into getting an 11"-class scope over decade ago, I was put off by the poor image quality and the poor focusing mechanics of Celestron's offerings at the time (I never had and still don't have a preferred one scope design, so don't over interpret my observations). I looked into the latter and realized why it worked so poorly and how that issue could be easily mitigated. When I mentioned this on a SCT blog, I was soundly chastised for my blasphemy! Keeping one's head in the sand is absurd. Now, if the new crop of SCTs have improved optical and thermal performance, I could be interested.


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EFT
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6227811 - 12/01/13 07:49 PM

Quote:

Quote:

Quote:

on that view all is compromise.




No it's not. With 8-inches of aperture, you can see a lot of deep sky objects and details in may of them. In a 3 or 4-inch APO? Not so much. You can't defeat the laws of physics by throwing money at them.




You can see far more with a 20" Dob, and they aren't prohibitively expensive.




The 20" Newt (Dob is a mount) is great, but I prefer not to have to climb up a 16 foot ladder to start at f/10.


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WadeH237
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Re: Why do people even buy SCTs??? new [Re: EFT]
      #6227890 - 12/01/13 08:24 PM

Quote:

The 20" Newt (Dob is a mount) is great, but I prefer not to have to climb up a 16 foot ladder to start at f/10.




Why would you do that? A 20" F/3.8 is about the same focal length as an 8" F/10 SCT and doesn't require a ladder. For big light grasp at an achievable price, it's hard to beat a newt on a dobsonian mount.

Of course, everything is a tradeoff. That fast newt is going to be extremely sensitive to collimation. Its critical focus zone is going to be razor thin. It may have issues with narrow band filters. It's going to have limited back focus.

I've not had time to go through this thread, but I see two advantages to SCTs: Versatility and packaging. They may not be the best option at any given use, but they are going to be "good enough" at just about every use. The second advantage is that they pack a lot of aperture into their size and weight.

If I were forced to live with only one telescope, it would be an 8" SCT.


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jgraham
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Re: Why do people even buy SCTs??? new [Re: WadeH237]
      #6227928 - 12/01/13 08:45 PM

+1 on the 8" SCT.

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JJK
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Re: Why do people even buy SCTs??? new [Re: EFT]
      #6227980 - 12/01/13 09:17 PM

Quote:

Quote:

Quote:

Quote:

on that view all is compromise.




No it's not. With 8-inches of aperture, you can see a lot of deep sky objects and details in may of them. In a 3 or 4-inch APO? Not so much. You can't defeat the laws of physics by throwing money at them.




You can see far more with a 20" Dob, and they aren't prohibitively expensive.




The 20" Newt (Dob is a mount) is great, but I prefer not to have to climb up a 16 foot ladder to start at f/10.




Almost everyone here knows that the term "Dob" is colloquially applied to large Newtonian telescopes. I'm sure Newton wouldn't care about such usage.

FWIW, the 20" Obsession Dob-Newt I had didn't require a 16-foot ladder. These things used to come in relatively short focal ratios like 4.5 and 5 (even faster now in others' models). If you require a relatively long focal length for image scale, you don't need f/10 when you have a 20" primary mirror (the math is easy). I used a 3 step ladder (Little Giant Type 1A Safety Step Step-stool) with 7" deep non-slip rubber-coated steps, with a safety bar at the top one can hold onto). I usually used 0, 1, or 2 steps and it was a really comfortable viewing experience.

If you're really afraid of heights (I would certainly understand not wanting to go higher than 5' off the ground in the dark), the 18" Obsession or its equivalent requires at most a 6-pack of beer as a step stool to observe at Dobson's Hole.

Why would you want a 20" f/10 scope?

I regrettably sold that 20" Obsession (that had a pick of the litter Galaxy Optics primary). It provided phenomenal tack-sharp images. I used to store the scope in my Living Room and when I wheeled it outside, the thermals were terrible (no surprise; I should have stored it in my garage to shorten the equilibration time). Over time, what others call "tube currents" improved and a few hours after bringing it outside, the mirrors figure snapped into place. After that, M42 was a sight to behold (tack sharp E & F Trap stars, a sprinkling of reddish-appearing jewel-like stars in the heart of the nebula just S of the Trap, very deep and smokey nebulosity, the obvious blue/green nebulosity, thundercloud purple in the gossamer wings, obvious pastel rose, orange, yellows). The North American Nebular looked better than any B & W film image I've seen, the even the Trifid showed pastel colors (beyond the normal green and blue one perceives with any decent size scope). I resolved Omega Centauri to the core from a mountain ridge in WV (the cluster was only 3* off the horizon, we had great seeing that night).


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JJK
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Re: Why do people even buy SCTs??? new [Re: WadeH237]
      #6227991 - 12/01/13 09:23 PM

Quote:

Quote:

The 20" Newt (Dob is a mount) is great, but I prefer not to have to climb up a 16 foot ladder to start at f/10.




Why would you do that? A 20" F/3.8 is about the same focal length as an 8" F/10 SCT and doesn't require a ladder. For big light grasp at an achievable price, it's hard to beat a newt on a dobsonian mount.

Of course, everything is a tradeoff. That fast newt is going to be extremely sensitive to collimation. Its critical focus zone is going to be razor thin. It may have issues with narrow band filters. It's going to have limited back focus.

I've not had time to go through this thread, but I see two advantages to SCTs: Versatility and packaging. They may not be the best option at any given use, but they are going to be "good enough" at just about every use. The second advantage is that they pack a lot of aperture into their size and weight.

If I were forced to live with only one telescope, it would be an 8" SCT.




Mine would be the AP 175 f/8. It's a great astrograph (the optional focal reducer/flattener gets you to f/6.1 or it can be used near prime focus at f/8.3 with the standard field flattener), and a superb visual instrument.


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Ed Wiley
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Re: Why do people even buy SCTs??? new [Re: Cotts]
      #6228050 - 12/01/13 09:58 PM

I'm with Cotts on this one, otherwise it would not be possible for me to image doubles at F50 with my C11 and get within 0.2" of the Dawes Limit.

Ed


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Dwight J
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6228115 - 12/01/13 10:46 PM

SCT's may not be everyone's whipping boy, certainly not mine nor Uncle Rod's and many satisfied users. As far as bargain prices, they may be more economical to buy now but in 1983 my Super C8 cost $2000.
I do know what it is like to look through top quality optics. When I obtained my MN and compared it to my C8, the difference in contrast was obvious and my C8 was no slouch. It tested out as a very good example by Peter Cerevolo. The MN is optimized for visual and many cameras do not reach focus and the fan needs to run for optimal views. So even though it is a premium scope, it isn't completely capable in all areas. It also weighs more than my C11. The SCT design is capable in all areas but excels in almost none.


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JJK
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Re: Why do people even buy SCTs??? new [Re: Ed Wiley]
      #6228129 - 12/01/13 10:51 PM

Quote:

I'm with Cotts on this one, otherwise it would not be possible for me to image doubles at F50 with my C11 and get within 0.2" of the Dawes Limit.

Ed




Ed, are these doubles with roughly equally bright partners?

As you know, a central obstruction (CO) can make it easier to split close double stars of nearly equal intensity because it takes some energy out of the central peaks. However, a CO is presumably less helpful if the binary is composed of a relatively bright star and a relatively dim partner. I'd be interested in knowing at which point the advantage the CO brings to the table in this measurement is lost.


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kbastro
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Re: Why do people even buy SCTs??? new [Re: Dwight J]
      #6228286 - 12/02/13 01:08 AM

My on again and off again relationship with the SCT is that the bloody things are heat traps and dew magnets..

BUT on the good side they are not wind magnets and are easy to work with,,

the bad, they don't beat my refractors or reflectors for sharpness..

the good, a one man portable observatory type instrument (C14) with tons of accessories..

the bad, just calculate how many lens/mirror surfaces an edge hd scope has to go through with an attached focal reducer as compared to a Mak newt to form an image on your ccd

kbastro


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drago
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Re: Why do people even buy SCTs??? new [Re: Itz marcus]
      #6228319 - 12/02/13 01:57 AM

Quote:

Hi,
I didn't go for a sct because I was afraid of collimation and I also believed what was said about the co. I used my Eon 120 for he last 7 years? Man do I love he scope but I did want something bigger and I couldn't afford a six inch apo or a long focus achro (and I wanted an eight inch scope ). I finally took the plunge and bought. Used c8 at a fraction of the price of a used 120 Ed scope. Although I have to service it as the scope wouldn't hold collimation, when it was in collimation the views were amazing. Things were easier to see and I was able to see more in my light poisoned city than the 120. I hope to be able to keep the 120 but if I can't afford to keep both then it looks like the c8 will be the scope to stay and as much as I really love the Eon 120 I will reluctantly let it go.
Clear skies
Itz




Traitor!
But - you say, you want a 8" size. there are any objective limitation to this size, or you also can be get a 10 - 12" dob?
i think, if you compare 12" with your 8" sct, you fast "let 8" to go"...;)


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mmalik
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Re: Why do people even buy SCTs??? new [Re: Dwight J]
      #6228364 - 12/02/13 03:29 AM

Quote:

The SCT design is capable in all areas but excels in almost none.




Well, isn't that the whole point? I think we are all going in circles trying to say the same thing but in different ways. Regards


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aa6ww
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Re: Why do people even buy SCTs??? new [Re: jrbarnett]
      #6228377 - 12/02/13 04:03 AM

I keep buying and selling C8's. I don't get it. Ive had 6 or 8 of them now since the mid 80's. They have all been excellent scopes. I have tons of scopes, but the my Orange tube C8 gets the most use when I'm just by myself in my back yard. Especially now that the weather is colder, my vixen mount sets up fast and the my entire set up takes 5 minutes to get running. When I'm out with my friends under darker skies, my C11 gets the most uses.
I have tons of expensive refractors. I should just keep my TOA and sell the rest of them. I never use them.
SCT's are addicting. I have some weird love affair with C8's. It's very strange.

It's a fun addiction. I just sold an Edge 8 and want another one again! They shoulda made a C6 Edge. They should also make a carbon fiber C8 Edge!

...Ralph


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Baxstar
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Re: Why do people even buy SCTs??? new [Re: aa6ww]
      #6228399 - 12/02/13 05:07 AM

I really like my C9,25! I really like the viewing position, and with a newton i can be very awkward to look in the EP.

But I get your point. No it isn't the best scope right of the bet.. BUT! If you correct it you have a very very powerful scope! A dutch astronomer has corrected several scopes and the and now they are way and i mean WAY BETTER than any Newton or Dobson. No coma or any other errors, very stable image because they air inside the SCT is blown around. Just the air inside, not taking are from the outside. This way the air in de SCT get more homogeneous. And he re coated the corrector! AMAZING machine!

Casper


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: Baxstar]
      #6228408 - 12/02/13 05:25 AM

2Baxstar: air inside too can boil from thermal currents.
and try understand: light from observing objects cross tube inside currents ( if any):
in refractor: one time
in newtonian: two times
in SCT and MCT: three times.
as you would expect, the more crosses - the more is influence.
i not comment another your allegations...


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Joe Aguiar
Carpal Tunnel
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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6228605 - 12/02/13 09:00 AM

OMG
i leave CN for one weekend and this thread goes from page 2 to 9 pages??


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orion61

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Re: Why do people even buy SCTs??? new [Re: Joe Aguiar]
      #6228903 - 12/02/13 11:30 AM

I guess then the perfect optical system should be,
1.. Somewhat easy to make,

2..Not have a central obstruction,

3..No false color

4..Inexpensive to Produce
Ladies and Gentlemen you have just described a *********************Schiefspiegler!************************


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TG
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6229084 - 12/02/13 01:01 PM

Quote:

When I was looking into getting an 11"-class scope over decade ago, I was put off by the poor image quality and the poor focusing mechanics of Celestron's offerings at the time (I never had and still don't have a preferred one scope design, so don't over interpret my observations).
<snip>
Now, if the new crop of SCTs have improved optical and thermal performance, I could be interested.




JJK, here's my take on Celestron SCTs, having owned 4 (3 Celestron, 1 Takahashi):

- Optical quality: mine ranged from run of the mill (a NexStar C11) to superb (my current C11HD). In the middle were a C9.25 (excellent) and a TSC-225, (slightly better than the C9.25 but not by a whole lot). See this recent thread about the C11HD's performance. My erstwhile C9.25 Roddier tested at 1/6 wave, 1/30 wave RMS (in green), an excellent optic by any measure. Taking it to 400x on Saturn was easy. The C11HD has such a good star test that I haven't bothered Roddier testing it, though that's on the todo list. To top it, it has a very flat field and is coma corrected. E.g., the components of the Double-Double look the same no matter where you place them in the field. But where it really shines is with lunar viewing because the entire field, with a decent eyepiece, is sharp. I sold the NS11 because I just couldn't stand its field curvature and coma. Otherwise, it had the terrific Gen 1 NS fork mount.

One thing that Celestron really paid attention to with the HD scopes is properly centering the corrector. I think a mis-centered corrector was the SCT bugaboo for the longest time resulting in poorer optical performance. They used to put in cork shims to center it and this probably wasn't very accurate to begin with and who knows what happened to the shims with time. My C9.25 showed a small amount of astigmatism in the Roddier test and I suspect that came from the corrector not being absolutely centered. Removing its effect made its RMS score distinctly better so there some performance lost here. With the HD scopes (and possibly some non-HD ones), they use centering screws on the corrector cell.

It's also recently come to light (with photographic proof) that Celestron assembles C11HD and C14HDs in California. So, I think they're paying more attention to at least this subclass.

- Focusing shift: It's gotten better over time. Celestron claims that they reject scopes showing more than 30 arcsec. My C11HD arrived with about 20 arcsec but it's gotten worse over time. I wonder if the primary mirror locknut has worked loose. The TSC225 was the best in this regard: almost no shift at all but the focuser was much harder to turn so I suspect it had some kind of spring loading. The HD scopes come with mirror locks, of course. It's a pity Celestron didn't re-introduce the 3-spindle belt-driven shift-free focuser which they probably invented and A-P borrowed for their Mak.

- Thermal management: The vents on the HD scopes help but are insufficient by themselves. Fortunately, there are the TEMPest fans from Deep Space Products which fit into the vents and both Starizona and DSP sell fans to put into the secondary. I am really uncomfortable with the secondary fan: taking the secondary out to cool the scope gives me heartburn but if you have a limited amount of time, it will cool your scope really fast. However, I find that in our climate, even the fans are unable to keep up with drops in temperature. I've constructed a Reflectix thermal blanket to keep the tube temperature stable once it cools to ambient and it really helps. This isn't scope specific, I think even the AP Mak would run into trouble with the top part of the tube cooling more than the bottom part.

- Misc. mechanicals: The Fastar secondary retaining ring still has the seizing problem. A simple solution, which Starizona sells, would be to install a better gasket. Fortunately, I don't do remove it often so I'm not particularly affected.

Digression: Many people worry unnecessarily about sub-mm play of the secondary in the corrector. It doesn't matter because the secondary is spherical. Any lateral shift can be corrected out by tilting it. All that'll happen is that the secondary shadow may be a tiny bit off-center, with uneven field illumination as well but this would take careful measurement with a CCD to figure out. But what you don't want is a loose secondary holder causing play. Every time it shifts it'll mess collimation up. Tighten it down but centering it is not required.

All this said, if you're looking for an A-P like guarantee, you won't find it, not at Celestron prices. Buying used may be a good strategy since you can recover all of the cost if you don't like the scope.

Tanveer.


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ATM57
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Re: Why do people even buy SCTs??? new [Re: Baxstar]
      #6229198 - 12/02/13 01:50 PM

Quote:

I really like my C9,25! I really like the viewing position, and with a newton i can be very awkward to look in the EP.

But I get your point. No it isn't the best scope right of the bet.. BUT! If you correct it you have a very very powerful scope! A dutch astronomer has corrected several scopes and the and now they are way and i mean WAY BETTER than any Newton or Dobson. No coma or any other errors, very stable image because they air inside the SCT is blown around. Just the air inside, not taking are from the outside. This way the air in de SCT get more homogeneous. And he re coated the corrector! AMAZING machine!

Casper




I wonder where he got the idea to recirculate the air in the ota? I have been doing this for a long time and have published articles on the subject.

Scopejunkie


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WesC
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6229208 - 12/02/13 01:57 PM

Quote:

2Baxstar: air inside too can boil from thermal currents.
and try understand: light from observing objects cross tube inside currents ( if any):
in refractor: one time
in newtonian: two times
in SCT and MCT: three times.
as you would expect, the more crosses - the more is influence.
i not comment another your allegations...





At the speed of light? Really? That's just silly. False logic. It could cross 10,000 times and you would not see any detectable difference. Moving air in a tube is billions of times slower than the speed of light, it will not influence the light more just because its in the tube for a trillionth of a second longer.

Anyway, once you stabilize the tube, its a non-issue. My C11 Edge stabilizes in around 20-30 minutes with the TEMPest fans I have. That's about as long as it takes me to setup, balance and align the GEM.


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saemark30
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Re: Why do people even buy SCTs??? new [Re: WesC]
      #6229234 - 12/02/13 02:06 PM

My old C11 has a problem with mirror tilting with changing azimuth. Has anyone experienced this, it would throw the collimation way off.

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csrlice12
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Re: Why do people even buy SCTs??? new [Re: jimbo728]
      #6229257 - 12/02/13 02:17 PM

Well, we needed some way to recycle all those toilet paper tubes........and they aren't long enough for dobs.

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ATM57
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Re: Why do people even buy SCTs??? new [Re: saemark30]
      #6229259 - 12/02/13 02:20 PM

Quote:

My old C11 has a problem with mirror tilting with changing azimuth. Has anyone experienced this, it would throw the collimation way off.




I had an orange tube that did this. The primary retaining ring was loose. A loose secondary holder can mimic this as well.

Scopejunkie


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drago
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Re: Why do people even buy SCTs??? new [Re: WesC]
      #6229281 - 12/02/13 02:30 PM

Quote:



At the speed of light? Really? That's just silly. False logic. It could cross 10,000 times and you would not see any detectable difference. Moving air in a tube is billions of times slower than the speed of light, it will not influence the light more just because its in the tube for a trillionth of a second longer.




hot air speed over a campfire is also lot less speed than a speed of light, but you can see, it changes view throught it very dramatically. turbulence in atmosphere, as so as tube currents also is not faster speed than speed of light, but that also destroy a views. looks like you can have a very big problems with elementar physic understanding...


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ATM57
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Re: Why do people even buy SCTs??? new [Re: orion61]
      #6229439 - 12/02/13 03:27 PM Attachment (13 downloads)

Quote:

I guess then the perfect optical system should be,
1.. Somewhat easy to make,

2..Not have a central obstruction,

3..No false color

4..Inexpensive to Produce
Ladies and Gentlemen you have just described a *********************Schiefspiegler!************************




Bulit one. True optical perfection in a minimalist design in both optics and mechanics. High res performance was off the chart for a 6". At F/29 is was a specialised instrument. I have a 10" two mirror on the drawing board but I can't find anyone who can make the optics. No, I'm not a glass pusher

Scopejunkie


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orion61

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Re: Why do people even buy SCTs??? new [Re: ATM57]
      #6229674 - 12/02/13 05:01 PM

I agree 100% the standard SCT's can be made to perform much better, I have been using a Micrometer and lasers to align
mirrors for years now. It is a part of the service i go.
The problem is when you get into Commercial manufacturing
it begins to be good money thrown after bad time in the form of performance. The ave. SCT with 10 extra hours can be made to perform better, but if they took the extra time
during fabrication it would add hundreds of dollars to the price.
I have learned not to trust the alignment marks 100%.
I believe newer scopes have developed ways to get some of these things much closer.
I had a Meade 10" where the corrector factor markings were close to 1/3 of a rotation out. The difference in views was enough to change the system from fair to VG.
Factory installed active cooling will be the next big thing. The optics are pretty much there now.
BTW Nice Schief ATM57! Beautiful build quality.
Now a shorter FL with a field corrector and they will be an every day scope...


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maknewtnut
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Re: Why do people even buy SCTs??? new [Re: saemark30]
      #6229760 - 12/02/13 05:36 PM

Quote:

My old C11 has a problem with mirror tilting with changing azimuth. Has anyone experienced this, it would throw the collimation way off.




Ask Rod. He'll tell you you and everyone else that has ever experienced such a condition is wrong.


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rmollise
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Re: Why do people even buy SCTs??? new [Re: maknewtnut]
      #6229767 - 12/02/13 05:40 PM

Quote:


Ask Rod. He'll tell you you and everyone else that has ever experienced such a condition is wrong.




No but I'll tell you you're wrong to start with.

OP: This condition as you were told can afflict some C11s, and is due to the primary being loose on the baffle due to a problem with the retainer.


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Vondragonnoggin
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6229787 - 12/02/13 05:48 PM

Where's the OP? He threw a ball of catnip into the cats and casses forum and hasn't returned yet. Watching the cats walk around with tape on their feet most likely....



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NHRob
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Re: Why do people even buy SCTs??? new [Re: Vondragonnoggin]
      #6229804 - 12/02/13 05:53 PM

He's probably scared away.
Likely looking in the reflector and refractor forums now.


Quote:

Where's the OP? He threw a ball of catnip into the cats and casses forum and hasn't returned yet. Watching the cats walk around with tape on their feet most likely....






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kansas skies
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6229881 - 12/02/13 06:24 PM

Why do people even buy SCTs???

Come on guys, it was the Celestron girls...

Bill


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Doug Culbertson
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Re: Why do people even buy SCTs??? new [Re: kansas skies]
      #6229893 - 12/02/13 06:28 PM

Quote:

Why do people even buy SCTs???

Come on guys, it was the Celestron girls...

Bill




That and the Leonard Nimoy ad!


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: Doug Culbertson]
      #6230002 - 12/02/13 07:21 PM

Mirror Flop: I don't know if it's a problem with the retainer ring or they just leave them loose for fear of pinching the optics. I just rebuilt my new C90 and the mirror was so loose, I had the issue with that little thing. I also used masking tape on the baffle slider to take up the slop of the difference in the mirror bore and the size of the slider tube. The alignment is much better as is the image. I did some bumping it around hard and alignment is still dead on.

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TG
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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6230068 - 12/02/13 07:45 PM

Quote:

Mirror Flop: I don't know if it's a problem with the retainer ring or they just leave them loose for fear of pinching the optics. I just rebuilt my new C90 and the mirror was so loose, I had the issue with that little thing.




Somebody at Celestron needs to be told about neoprene gaskets.

Tanveer


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WesC
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6230078 - 12/02/13 07:49 PM

Quote:

Quote:



At the speed of light? Really? That's just silly. False logic. It could cross 10,000 times and you would not see any detectable difference. Moving air in a tube is billions of times slower than the speed of light, it will not influence the light more just because its in the tube for a trillionth of a second longer.




hot air speed over a campfire is also lot less speed than a speed of light, but you can see, it changes view throught it very dramatically. turbulence in atmosphere, as so as tube currents also is not faster speed than speed of light, but that also destroy a views. looks like you can have a very big problems with elementar physic understanding...




Nice cheap shot there. You know nothing about me or my level of education. But thanks for taking potshots anyway.

FWIW, you're still incorrect.


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WesC
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Re: Why do people even buy SCTs??? new [Re: TG]
      #6230079 - 12/02/13 07:49 PM

Quote:


Somebody at Celestron needs to be told about neoprene gaskets.

Tanveer




And modern lubricants.


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: WesC]
      #6230092 - 12/02/13 07:55 PM

The bad thing is, it's got a 1/32" cardboard washer on the front side and a 1/8" O-ring on the back side under the jam nut. A quarter turn would of been enough to do the job once the nut was touching. The right parts are there, they just didn't use them right...

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rmollise
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Re: Why do people even buy SCTs??? new [Re: TG]
      #6230164 - 12/02/13 08:33 PM

Quote:

Quote:

Mirror Flop: I don't know if it's a problem with the retainer ring or they just leave them loose for fear of pinching the optics. I just rebuilt my new C90 and the mirror was so loose, I had the issue with that little thing.




Somebody at Celestron needs to be told about neoprene gaskets.

Tanveer




Mirror flop is not caused by the retainer ring being loose. If it is loose, you will have problems, sure, but that is rare. Mirror flop is the mirror/carrier moving on the baffle.


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6230250 - 12/02/13 09:08 PM

In my C90, it was the ring being loose. The bore in the mirror was about .060" larger than the baffle slider tube. Even with it out in hand, you could turn it and the mirror would go clunk each time. Holding the slider in hand, without it being on the primary baffle, you could just touch the mirror with the other hand and wiggle it back and forth with no effort. Also, in this C90, there was no play between the primary baffle and the slider, even with all the grease washed off and the unit squeaky clean. Proof is, I put the unit back together with only a film of grease from a paper towel. I have no play or flop now. While that may not be the norm, it was the cause 100% in this C90.

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azure1961p
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Re: Why do people even buy SCTs??? new [Re: WesC]
      #6230337 - 12/02/13 09:43 PM

Quote:

Quote:

Quote:



At the speed of light? Really? That's just silly. False logic. It could cross 10,000 times and you would not see any detectable difference. Moving air in a tube is billions of times slower than the speed of light, it will not influence the light more just because its in the tube for a trillionth of a second longer.




hot air speed over a campfire is also lot less speed than a speed of light, but you can see, it changes view throught it very dramatically. turbulence in atmosphere, as so as tube currents also is not faster speed than speed of light, but that also destroy a views. looks like you can have a very big problems with elementar physic understanding...




Nice cheap shot there. You know nothing about me or my level of education. But thanks for taking potshots anyway.

FWIW, you're still incorrect.




I've got to agree with Wesc here it is apparent for the reasons mentioned. It seems infinitesimally minuscule and how after all could such a fine discrepancy be witnessed by and eye/brain but alas light spells it out unmistakably - even exceedingly sensitive at that. I had questions of this sort - and not THAT long ago. At the point of focus (and on either side) its plain as day. I am sympathetic to your questioning it - but once you see how light fleshes out these discrepancies it all makes sense. Even within the extremely short distance of an optical assembly. Doesn't matter. It reveals all.

Pete


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orion61

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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6230356 - 12/02/13 09:51 PM

A lot of mirror shift is from the grease being too thick,
Super Lube cut with Synthetic oil, has eliminated mirror shift in about a dozen scopes I have worked on.
ESPECIALLY 7" Meade Maks, & 10" Cats. Meade 12 & up have a Coil Spring that assists focus. Meade scopes seem to suffer more than Celestron
Someone mentioned it but I agree, the belt drive focus of the 127 Maksutov I have is a great example of smooth focus..
I think it is time to say, we like the type of scopes we do for reasons "individual as we are". There isn't a wrong type of scope design (well possibly Jones-Bird)
I stand by my Schmidts because they fit my direction in this hobby, ease of storage, transportation,optical quality and purchase price.,
IF I had about 10k laying around I might think about a Premium APO for Lunar/Planetary work.
But a 9.25-11" Cat with a mid FL eyepiece (ND or polarizer filter to cut down on the overwhelming brightness) can match an APO working hard to reach the same power.
Newtonians, are harder to compete against. I have an old 826
Meade F6 tube that is pretty tough for an average 8" Schmidt to equal, I have seen it done with my Henzl C8 but it has custom optics. But wind loading and the large GEM's
are just too much of a pain for me.
I will stick to my Kitty Cats.


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EFT
Vendor - Deep Space Products
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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6230360 - 12/02/13 09:53 PM

Quote:

In my C90, it was the ring being loose. The bore in the mirror was about .060" larger than the baffle slider tube. Even with it out in hand, you could turn it and the mirror would go clunk each time. Holding the slider in hand, without it being on the primary baffle, you could just touch the mirror with the other hand and wiggle it back and forth with no effort. Also, in this C90, there was no play between the primary baffle and the slider, even with all the grease washed off and the unit squeaky clean. Proof is, I put the unit back together with only a film of grease from a paper towel. I have no play or flop now. While that may not be the norm, it was the cause 100% in this C90.




I think that the C90 must be different than the larger Celestron SCTs. The 8 inch and above have the primary glued in place. The only primary mirror shift in those OTAs comes from the clearance between the baffle tube the primary mirror carrier. I have never seen a primary loose on the carrier in a larger Celestron SCT.

Meade SCTs on the other hand have the primary sandwitched between a couple of gaskets and held in place by a retaining ring. Those I have seen those loose.


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: EFT]
      #6230388 - 12/02/13 10:03 PM Attachment (20 downloads)

Here's what mine looked like:

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EFT
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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6230456 - 12/02/13 10:31 PM

That looks a lot more like the Meade SCTs I have worked on where the primary is held onto the carrier by being sandwitched between a support and locking ring and can move around on the carrier if the ring or the gaskets are loose. The Celestron method is more stable, but if you ever run into the rare occasion where you want to recoat a primary, the Meade system is a lot easier to take apart. Of course the Meade OTA is more difficult to take apart since it is glued together. Both companies apply glue in different places.

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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: WesC]
      #6230515 - 12/02/13 11:05 PM

Quote:

Quote:

Quote:



At the speed of light? Really? That's just silly. False logic. It could cross 10,000 times and you would not see any detectable difference. Moving air in a tube is billions of times slower than the speed of light, it will not influence the light more just because its in the tube for a trillionth of a second longer.




hot air speed over a campfire is also lot less speed than a speed of light, but you can see, it changes view throught it very dramatically. turbulence in atmosphere, as so as tube currents also is not faster speed than speed of light, but that also destroy a views. looks like you can have a very big problems with elementar physic understanding...




Nice cheap shot there. You know nothing about me or my level of education. But thanks for taking potshots anyway.

FWIW, you're still incorrect.





Wes, are you suggesting that the path of a light beam passing through turbulent air (i.e., spatially varying indices of refraction) isn't perturbed?

Edited by JJK (12/02/13 11:10 PM)


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: EFT]
      #6230527 - 12/02/13 11:17 PM

My C6 is the same as the C90, no glue. My Meade LX200's, the 8 and 14 also have no glue. People say Meade uses glue but it is not in mine that I can see, which are older units. I have had the 8 and 14 Meade units apart a few times for a good cleaning and found no glue. I did find that Meade press fits the OTA end caps to the tube which I like better as there can be no shift to the end caps and there could be some glue there that can not be seen. However, they are easy enough to pull down if you know the units. The Meade units I have, have better light baffles. But they are the larger units. I have not been into the larger Celestron units though.

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EFT
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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6230587 - 12/03/13 12:23 AM

Quote:

My C6 is the same as the C90, no glue. My Meade LX200's, the 8 and 14 also have no glue. People say Meade uses glue but it is not in mine that I can see, which are older units. I have had the 8 and 14 Meade units apart a few times for a good cleaning and found no glue. I did find that Meade press fits the OTA end caps to the tube which I like better as there can be no shift to the end caps and there could be some glue there that can not be seen. However, they are easy enough to pull down if you know the units. The Meade units I have, have better light baffles. But they are the larger units. I have not been into the larger Celestron units though.




It's the glue where the front and rear cells are pressed onto the tube that I was referring to. I haven't had the occasion to take apart a C6 so that could be the same as the C90. The C8 and above has the primary glued onto the carrier.


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WesC
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6230653 - 12/03/13 01:43 AM

Quote:


Wes, are you suggesting that the path of a light beam passing through turbulent air (i.e., spatially varying indices of refraction) isn't perturbed?





Absolutely not!

What I am, and have been saying is that it doesn't become visibly MORE perturbed by the light passing through the disturbed air more than once. Its does it all so fast and to such a small degree that the cumulative effect isn't much different that it would be if it passed though that same air once.

Could it be mathematically measured? Maybe, but I'm doubtful.

Could the human eye detect it? No way.


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drago
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Re: Why do people even buy SCTs??? new [Re: WesC]
      #6230722 - 12/03/13 02:49 AM

Quote:

Quote:


Wes, are you suggesting that the path of a light beam passing through turbulent air (i.e., spatially varying indices of refraction) isn't perturbed?





Absolutely not!

What I am, and have been saying is that it doesn't become visibly MORE perturbed by the light passing through the disturbed air more than once. Its does it all so fast and to such a small degree that the cumulative effect isn't much different that it would be if it passed though that same air once.

Could it be mathematically measured? Maybe, but I'm doubtful.

Could the human eye detect it? No way.





but that light beam no cross the air in same manner.
until it drops to primary - it carrier a wide beam. when it was in way from primary to secondary - it is a conical beam from prinmary to secondary diameter, and so on. as so, turbulent layer each time the light cross it, disturb the image in various way.
even it is not that, if cross always is the same light, the errors from turbulence summs. 1+1+1 =! 1
deformed wavefront becomes more deformed, when you get it throught the same deforming conditions again.

P.S. do you also think, your understanding cannot be see from your posts? Do you also think, "education" is equal to "understanding", and become a anyone "smart" ?


Edited by drago (12/03/13 02:50 AM)


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JJK
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Re: Why do people even buy SCTs??? new [Re: WesC]
      #6230762 - 12/03/13 04:30 AM

Quote:

Quote:


Wes, are you suggesting that the path of a light beam passing through turbulent air (i.e., spatially varying indices of refraction) isn't perturbed?





Absolutely not!

What I am, and have been saying is that it doesn't become visibly MORE perturbed by the light passing through the disturbed air more than once. Its does it all so fast and to such a small degree that the cumulative effect isn't much different that it would be if it passed though that same air once.

Could it be mathematically measured? Maybe, but I'm doubtful.

Could the human eye detect it? No way.




Perhaps I don't understand your point, but in a compound telescope like a SCT, a given light ray doesn't trace the same path after hitting either the f/2 primary or the secondary. In addition, it's extremely likely that at a fixed distance from the corrector, the index of refraction of the air in the tube varies along the radius. The same is true of all rays entering the scope. Thus, at a given distance from the corrector, a given ray will likely pass through three different index of refraction "boundaries".

Now, because the sum of all light rays become focused as they are reflected into the baffle tube, it's conceivable that some of the "tube currents" are caused by the single pass through a relatively warm narrow baffle. It's also possible that the turbulent boundary layer above a relatively warm primary contributes to the patterns visible at the focal plane.


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JJK
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Re: Why do people even buy SCTs??? new [Re: azure1961p]
      #6230763 - 12/03/13 04:31 AM

Quote:

Quote:

Quote:

Quote:



At the speed of light? Really? That's just silly. False logic. It could cross 10,000 times and you would not see any detectable difference. Moving air in a tube is billions of times slower than the speed of light, it will not influence the light more just because its in the tube for a trillionth of a second longer.




hot air speed over a campfire is also lot less speed than a speed of light, but you can see, it changes view throught it very dramatically. turbulence in atmosphere, as so as tube currents also is not faster speed than speed of light, but that also destroy a views. looks like you can have a very big problems with elementar physic understanding...




Nice cheap shot there. You know nothing about me or my level of education. But thanks for taking potshots anyway.

FWIW, you're still incorrect.




I've got to agree with Wesc here it is apparent for the reasons mentioned. It seems infinitesimally minuscule and how after all could such a fine discrepancy be witnessed by and eye/brain but alas light spells it out unmistakably - even exceedingly sensitive at that. I had questions of this sort - and not THAT long ago. At the point of focus (and on either side) its plain as day. I am sympathetic to your questioning it - but once you see how light fleshes out these discrepancies it all makes sense. Even within the extremely short distance of an optical assembly. Doesn't matter. It reveals all.

Pete




???


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saemark30
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6231602 - 12/03/13 02:42 PM

Rod so the mirror flop only occurs with some C11s? How about C14s with heavier mirrors?
I know of one Meade 16 SCT LX200 had issues.


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rmollise
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Re: Why do people even buy SCTs??? new [Re: saemark30]
      #6231638 - 12/03/13 03:05 PM

Mirror flop can occur with ANY SCT in that there is always a little slop between carrier and baffle tube. If your focusing leaves it in an offbalance condition, it can move slightly when the scope changes in attitude, like from one side of the Meridian to the other. What was mentioned here is entirely different and much worse. I suppose it could afflict other scopes, but I have only seen it in older C11s.

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JJK
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6231648 - 12/03/13 03:12 PM

Quote:

Mirror flop can occur with ANY SCT in that there is always a little slop between carrier and baffle tube. If your focusing leaves it in an offbalance condition, it can move slightly when the scope changes in attitude, like from one side of the Meridian to the other. What was mentioned here is entirely different and much worse. I suppose it could afflict other scopes, but I have only seen it in older C11s.




Rod, many years ago, the issue with SCT mirror slop (non-uniform mirror movement when the focuser was turned) was caused by a poor design (two points do not define a plane), no doubt used to keep costs down (its hard to sell scopes at great prices by putting in Ferrari-level components). Do you know if Celestron & Meade have improved this issue, and if so, do you know how they did it? I'm a bit reluctant to ask someone at a star party if I can take the back of their scope off!


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Bruce FitzGerald
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6231652 - 12/03/13 03:14 PM

Sayonara, Eddgie! Guess we won't be seeing you around here anymore!

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Spacetravelerx
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6231668 - 12/03/13 03:23 PM

Quote:

Quote:

Mirror flop can occur with ANY SCT in that there is always a little slop between carrier and baffle tube. If your focusing leaves it in an offbalance condition, it can move slightly when the scope changes in attitude, like from one side of the Meridian to the other. What was mentioned here is entirely different and much worse. I suppose it could afflict other scopes, but I have only seen it in older C11s.




Rod, many years ago, the issue with SCT mirror slop (non-uniform mirror movement when the focuser was turned) was caused by a poor design (two points do not define a plane), no doubt used to keep costs down (its hard to sell scopes at great prices by putting in Ferrari-level components). Do you know if Celestron & Meade have improved this issue, and if so, do you know how they did it? I'm a bit reluctant to ask someone at a star party if I can take the back of their scope off!




JJK,

My Meade 14" f/8 ACF (new) does not experience focus shift, at least none I can detect. With my very old 10" LX200 it would drive me crazy! Mirror flop is also no existent with my 14", however this because I can lock the mirror.

Oh, I purchased my 14" SCT for the aperture and very good optics. Though I have also purchased 2 APOs. And I have a 125ETX…and… That is how I dealt with the issue - buy all types!


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: Spacetravelerx]
      #6231689 - 12/03/13 03:37 PM

Meade has not only improved it, but eliminated it! Their new baffle slider, is no longer a slider. It now rolls on six high precision bearings, like a Crayford focuser tube. All mirror flop is gone!

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JJK
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Re: Why do people even buy SCTs??? new [Re: Spacetravelerx]
      #6231696 - 12/03/13 03:42 PM

Quote:

Quote:

Quote:

Mirror flop can occur with ANY SCT in that there is always a little slop between carrier and baffle tube. If your focusing leaves it in an offbalance condition, it can move slightly when the scope changes in attitude, like from one side of the Meridian to the other. What was mentioned here is entirely different and much worse. I suppose it could afflict other scopes, but I have only seen it in older C11s.




Rod, many years ago, the issue with SCT mirror slop (non-uniform mirror movement when the focuser was turned) was caused by a poor design (two points do not define a plane), no doubt used to keep costs down (its hard to sell scopes at great prices by putting in Ferrari-level components). Do you know if Celestron & Meade have improved this issue, and if so, do you know how they did it? I'm a bit reluctant to ask someone at a star party if I can take the back of their scope off!




JJK,

My Meade 14" f/8 ACF (new) does not experience focus shift, at least none I can detect. With my very old 10" LX200 it would drive me crazy! Mirror flop is also no existent with my 14", however this because I can lock the mirror.

Oh, I purchased my 14" SCT for the aperture and very good optics. Though I have also purchased 2 APOs. And I have a 125ETX…and… That is how I dealt with the issue - buy all types!





That is very good news.

I agree that it doesn't pay to favor one kind of instrument. So far, mine run the gamut from apos, apos w/fluorite, Mak-Cass, Newt-Dob, CDKs. A good 14" SCT would be fun to play with for visual and imaging work.


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rmollise
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6231954 - 12/03/13 06:49 PM

Quote:

Quote:

Mirror flop can occur with ANY SCT in that there is always a little slop between carrier and baffle tube. If your focusing leaves it in an offbalance condition, it can move slightly when the scope changes in attitude, like from one side of the Meridian to the other. What was mentioned here is entirely different and much worse. I suppose it could afflict other scopes, but I have only seen it in older C11s.




Rod, many years ago, the issue with SCT mirror slop (non-uniform mirror movement when the focuser was turned) was caused by a poor design (two points do not define a plane), no doubt used to keep costs down (its hard to sell scopes at great prices by putting in Ferrari-level components). Do you know if Celestron & Meade have improved this issue, and if so, do you know how they did it? I'm a bit reluctant to ask someone at a star party if I can take the back of their scope off!




In my experience, flop and focus shift are better now. With the mirror locks on the Edge SCTs flop is, naturally, not a problem.


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The Ardent
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6232027 - 12/03/13 07:31 PM

Any chance there will be SCT's with fixed mirrors?

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EFT
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Re: Why do people even buy SCTs??? new [Re: The Ardent]
      #6232124 - 12/03/13 08:24 PM

Quote:

Any chance there will be SCT's with fixed mirrors?




You can already have this by either using a rear cell focuser or using one of Optec's SCT secondary focusers (I can't find them on the website, but they had them out at ASAE). Using either of those methods, the primary can be locked in place and left. Of course the secondary focuser still result in a moving mirror similar to that in a Mewlon 300.


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kbastro
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Re: Why do people even buy SCTs??? new [Re: EFT]
      #6232142 - 12/03/13 08:35 PM

there was one SCT that I would have liked to buy

takahashi tsc 225


kb


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jgraham
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Re: Why do people even buy SCTs??? new [Re: kbastro]
      #6232182 - 12/03/13 08:53 PM

I made a simple tensioner for my 10" LX6 that greatly reduced my focus-shift to he point that it has become a non-issue.

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JJK
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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6232260 - 12/03/13 09:33 PM

Quote:

Quote:

Quote:

Mirror flop can occur with ANY SCT in that there is always a little slop between carrier and baffle tube. If your focusing leaves it in an offbalance condition, it can move slightly when the scope changes in attitude, like from one side of the Meridian to the other. What was mentioned here is entirely different and much worse. I suppose it could afflict other scopes, but I have only seen it in older C11s.




Rod, many years ago, the issue with SCT mirror slop (non-uniform mirror movement when the focuser was turned) was caused by a poor design (two points do not define a plane), no doubt used to keep costs down (its hard to sell scopes at great prices by putting in Ferrari-level components). Do you know if Celestron & Meade have improved this issue, and if so, do you know how they did it? I'm a bit reluctant to ask someone at a star party if I can take the back of their scope off!




In my experience, flop and focus shift are better now. With the mirror locks on the Edge SCTs flop is, naturally, not a problem.




Thanks. I'll check out the new offerings.


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PowellAstro
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6232271 - 12/03/13 09:36 PM

Any of the meades with mirror lock are nice. Add a Crayford focuser, then adjust the main mirror where you need it, then lock it down.

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fjs
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6232290 - 12/03/13 09:47 PM

To the original post: The answer is obvious. It's all about convenience. Unit of aperture per unit of bulk, and at a reasonable price. The O.P. knows this. He wanted to start a discussion. I await the reason for it. What answer was he looking for?

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Spacetravelerx
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Re: Why do people even buy SCTs??? new [Re: PowellAstro]
      #6232374 - 12/03/13 10:38 PM

Quote:

Any of the meades with mirror lock are nice. Add a Crayford focuser, then adjust the main mirror where you need it, then lock it down.




The new Meade f/8 ACFs all have Internal Crayford focusers, and the LX850 and LX200 also come with Zero Image-Shift Microfocuser.

It was an epic leap from my old SCT. I won't lose any hair focussing, lol.


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maknewtnut
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Re: Why do people even buy SCTs??? new [Re: fjs]
      #6232473 - 12/03/13 11:39 PM

Quote:

To the original post: The answer is obvious. It's all about convenience. Unit of aperture per unit of bulk, and at a reasonable price. The O.P. knows this. He wanted to start a discussion. I await the reason for it. What answer was he looking for?




Frank nailed it.

Some continue their love affair with the design after decades. Others might seek attributes they feel the SCT can't provide, or don't provide on a consistent basis. Whatever attribute one might desire, it's impossible to deny those listed by Frank.

Damn near every telescope has what one person might consider pros and cons. The next person might recognize the same list of attributes, yet not consider a con to be of any consequence to them.

IMHO, issues such as the occasional poor fit between primary mirror and baffle or ever-thickening grease are minor (regardless of the design type or who produces it). They are easy and inexpensive to eliminate or minimize. The list goes on in that regard. Other issues that are not easy or cheap to 'fix' are a different story, and yet still subject to individual preference or perception.

Regardless of minor or major, common or uncommon, it's in the best interest of every participant of this forum to learn about how to maximize the performance of their scope, if they so desire. A majority of telescope mechanics really aren't that complex. Those with some mechanical ability and a few simple tools can handle much. A few extra tools, a bit of analysis and patience, attention to detail, and a never ending focus on keeping optical surfaces clean will allow you to accomplish most any mechanical issue a telescope could throw at you.

On a personal note...
Rod, I got a little feisty earlier in this thread. My apologies. You are considered by many to be an authority on the SCT. Tips about the cause of primary mirror flop is a fine example. It helps some folks make the very best of theirs. At the very least, it helps all to be informed and aware.

Is the mass produced the cat's meow for everyone? No. Nothing is.


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Ed Holland
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Re: Why do people even buy SCTs??? new [Re: maknewtnut]
      #6232498 - 12/04/13 12:14 AM

I appreciate the skepticism about SCTs, it keeps the second hand prices so affordable

That wonky used C8 turns out to be the best scope I have viewed with...


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Roy McCoy
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Re: Why do people even buy SCTs??? new [Re: Ed Holland]
      #6232508 - 12/04/13 12:26 AM

Quote:

I appreciate the skepticism about SCTs, it keeps the second hand prices so affordable




You're welcome.


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donnie3
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Re: Why do people even buy SCTs??? new [Re: jimbo728]
      #6232528 - 12/04/13 12:39 AM

my take on this subject with the experience I have through the years in the city and at dark sites is this, refractors shine in dark skies, if I lived in the Oklahoma hills (osage county)where its so dark you cant see 2 feet in front of you, the refractor would be the master scope but in town with sky glow, I consider them useless. reflectors and cats for the city. just my simple option. donnie

Edited by donnie3 (12/04/13 12:50 AM)


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drago
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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6232601 - 12/04/13 01:59 AM

Quote:


I agree that it doesn't pay to favor one kind of instrument. So far, mine run the gamut from apos, apos w/fluorite, Mak-Cass, Newt-Dob, CDKs. SCT would be fun to play with for visual and imaging work.




oh yes!
that CDK was great, isn't?
http://fidgor.narod.ru/Observers/Test/test_84.html

sorry, it's ODK, but anyway....


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JJK
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6232870 - 12/04/13 08:52 AM

Quote:

Quote:


I agree that it doesn't pay to favor one kind of instrument. So far, mine run the gamut from apos, apos w/fluorite, Mak-Cass, Newt-Dob, CDKs. SCT would be fun to play with for visual and imaging work.




oh yes!
that CDK was great, isn't?
http://fidgor.narod.ru/Observers/Test/test_84.html

sorry, it's ODK, but anyway....




You don't know much about CDKs, do you? I have a Tak Mewlon 300 CRS (which provides stunning refractor-like views) and a rare Ceravolo 300 f/4.9-f/9 Astrograph. The top manufacturers consider them as CDKs. These instruments have considerably better performance than the scope in that Russian report. BTW, do you read Russian?

http://www.optcorp.com/takahashi-mewlon-300crs-cdk-telescope-tlk3201.html
http://www.ceravolo.com/

Edited by JJK (12/04/13 09:07 AM)


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orion61

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Re: Why do people even buy SCTs??? new [Re: JJK]
      #6232885 - 12/04/13 09:00 AM

I thought Trolling threads were prohibited? That is what this one has turned out to be.

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ATM57
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Re: Why do people even buy SCTs??? new [Re: orion61]
      #6233472 - 12/04/13 02:22 PM

Quote:

I thought Trolling threads were prohibited? That is what this one has turned out to be.




Hey Orion61,
Let's see if we can get this thread back on track:

I bet the optics in you C-8 would surprise many as to how well a C-8 can perform. Since Leo was the VP of marketing for Celestron, the optics in your scope are more than likely one of the legendary smooth nulled sets. Inquiring minds want to know

Scopejunkie


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TG
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Re: Why do people even buy SCTs??? new [Re: drago]
      #6233525 - 12/04/13 02:52 PM

Quote:

Quote:


I agree that it doesn't pay to favor one kind of instrument. So far, mine run the gamut from apos, apos w/fluorite, Mak-Cass, Newt-Dob, CDKs. SCT would be fun to play with for visual and imaging work.




oh yes!
that CDK was great, isn't?
http://fidgor.narod.ru/Observers/Test/test_84.html

sorry, it's ODK, but anyway....




Drago, interesting site. I went to the root site http://fidgor.narod.ru and also went through all the test reports (I don't know if they're linked at the top, I just went through test_00.html, test_01.html, ... manually all the way).

Do you know what kind of interferometer they're using? And since I don't read Russian (and online translation is poor), can you tell me who these people are? I find it interesting that most of the scopes they tested showed up poor and almost all had coma and astigmatism that they removed from the final report. Are they displaying only bad ones or all? I can't tell.

Tanveer.


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JJK
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Re: Why do people even buy SCTs??? new [Re: TG]
      #6233558 - 12/04/13 03:11 PM

Quote:

Quote:

Quote:


I agree that it doesn't pay to favor one kind of instrument. So far, mine run the gamut from apos, apos w/fluorite, Mak-Cass, Newt-Dob, CDKs. SCT would be fun to play with for visual and imaging work.




oh yes!
that CDK was great, isn't?
http://fidgor.narod.ru/Observers/Test/test_84.html

sorry, it's ODK, but anyway....




Drago, interesting site. I went to the root site http://fidgor.narod.ru and also went through all the test reports (I don't know if they're linked at the top, I just went through test_00.html, test_01.html, ... manually all the way).

Do you know what kind of interferometer they're using? And since I don't read Russian (and online translation is poor), can you tell me who these people are? I find it interesting that most of the scopes they tested showed up poor and almost all had coma and astigmatism that they removed from the final report. Are they displaying only bad ones or all? I can't tell.

Tanveer.




The direct link is to a very thin report. The LHS of the web page says essentially you're on your own (caveat emptor). The bottom part suggests the optics might have been wiped by a less than pristine cloth. The method employed was autocollimation. I'll read it again later to get the details.

Edited by JJK (12/04/13 03:13 PM)


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gmartin02
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Re: Why do people even buy SCTs??? new [Re: orion61]
      #6233717 - 12/04/13 04:53 PM

Quote:

I thought Trolling threads were prohibited? That is what this one has turned out to be.




With a title like "Why do people even buy SCTs???", what did you expect? The title is begging: "troll me, troll me!"

Fortunately, I have resisted


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Calypte
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Re: Why do people even buy SCTs??? new [Re: gmartin02]
      #6233753 - 12/04/13 05:08 PM

Quote:


With a title like "Why do people even buy SCTs???", what did you expect? The title is begging: "troll me, troll me!"

Fortunately, I have resisted



That's what I thought this was from the beginning. Post a hyperbolic remark, then stand back and watch the fur fly.


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DesertRat
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Re: Why do people even buy SCTs??? new [Re: TG]
      #6233808 - 12/04/13 05:35 PM

On the Russian site referred to above if you go to:

http://fidgor.narod.ru/Observers/test.html

using Chrome to get a translation you'll find a list broken into groups of refractors, newts, etc.

You'll note that many of the big mirrors test awful, strehls < 0.3 are shown in some of them. As I mentioned in the recent WinRoddier thread, many times testing a large mirror horizontally is just as much a dignostic of the mirror mount than the optic. Mirror mounts are generally not designed for horizontal use. A sling might be called for to test the primary only.

I'm assuming they have a decent flat, or one that can be corrected for.

The practice of disabling coma and astigmatism in a report is ok as long as they also include the full report. Sometimes they do. I would expect smaller optics generally to test better than larger ones, but maybe not so wildly as they do on that site.

Perhaps many of these optics had previously known issues or complaints. Making any general statements about a given scope type would not be useful if that indeed is the case.

Glenn


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Asbytec
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Re: Why do people even buy SCTs??? new [Re: orion61]
      #6234237 - 12/04/13 09:17 PM

Quote:

I thought Trolling threads were prohibited? That is what this one has turned out to be.



I'm not sure this began as a troll thread with bad intentions so much as it is a defense of the SCT thread with good intentions. The OP, I think, simply asked a question about the design, being the whipping boy in our community, trying to argue in favor of the SCT - not bash it. His approach was to list everything bad we often hear about the design, and ask ironically, why we even consider buying them - and do buy them in droves, apparently. It may have become a troll thread in that it's beating a dead horse while attracting many replies from folks who are pro and con for the purpose of beating that horse (and the SCT.) It's rekindled the pro and con debate we see all the time with no final word, just firm opinions either way as always. Little will change.


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drago
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Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: JJK]
      #6234587 - 12/05/13 02:01 AM

Quote:


You don't know much about CDKs, do you? I have a Tak Mewlon 300 CRS (which provides stunning refractor-like views) and a rare Ceravolo 300 f/4.9-f/9 Astrograph. The top manufacturers consider them as CDKs. These instruments have considerably better performance than the scope in that Russian report. BTW, do you read Russian?






Wua-ha-ha!
see, tak mewlon has 32 percent secondary obstruction!
"refractor-like" views, you say? that must be very poor refractor...
and what exactly "considerably better performance" thats instruments have? what is strehl ratio?
and yes, i read in russian. i growing in soviet union, as so i know russian, and that is good. also as some another things in soviet.


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: TG]
      #6234593 - 12/05/13 02:09 AM

Quote:


Drago, interesting site. I went to the root site http://fidgor.narod.ru and also went through all the test reports (I don't know if they're linked at the top, I just went through test_00.html, test_01.html, ... manually all the way).

Do you know what kind of interferometer they're using? And since I don't read Russian (and online translation is poor), can you tell me who these people are? I find it interesting that most of the scopes they tested showed up poor and almost all had coma and astigmatism that they removed from the final report. Are they displaying only bad ones or all? I can't tell.

Tanveer.




as there is said, there is a root page for tests:
http://fidgor.narod.ru/Observers/test.html
the folks is from moscow VAGO - an amateur organization, who takes amateur astronomers, founded in soviet union times. there are a many smart and experienced folks, some of them also have a professional knowledge in astronomy optics.
i dont remember what type of IF hes used, but there is a more about all that:
http://www.astronomy.ru/forum/index.php/topic,21065.0.html
http://www.astronomy.ru/forum/index.php/topic,82347.0.html


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TheObserver
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Reged: 09/24/13

Loc: Light Polluted, NY
Re: Why do people even buy SCTs??? new [Re: drago]
      #6234612 - 12/05/13 02:49 AM

the last time someone showed up with sct to our meet up. first he had 2 horses helping him to pull that carriage . and by the time he setup and started observing we were having pizza. i would never consider buying something that big and heavy. i setup in 30seconds

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coopman
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Reged: 04/23/06

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Re: Why do people even buy SCTs??? new [Re: TheObserver]
      #6234788 - 12/05/13 07:51 AM

True dat! Too much patience required.

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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Why do people even buy SCTs??? new [Re: drago]
      #6234823 - 12/05/13 08:14 AM

Quote:

Quote:


You don't know much about CDKs, do you? I have a Tak Mewlon 300 CRS (which provides stunning refractor-like views) and a rare Ceravolo 300 f/4.9-f/9 Astrograph. The top manufacturers consider them as CDKs. These instruments have considerably better performance than the scope in that Russian report. BTW, do you read Russian?






Wua-ha-ha!
see, tak mewlon has 32 percent secondary obstruction!
"refractor-like" views, you say? that must be very poor refractor...
and what exactly "considerably better performance" thats instruments have? what is strehl ratio?
and yes, i read in russian. i growing in soviet union, as so i know russian, and that is good. also as some another things in soviet.




You obviously have no experience viewing through Tak Mewlon 300 telescopes. Every one I've looked through has produced excellent lunar and planetary views, and it's an acceptable DSO instrument (obviously, it doesn't go as deep as a large Newt-Dob). The CO in The Mewlon 300 is not a significant issue (if it was, I wouldn't have bought such a scope). If you believe it is, produce hard evidence for your case. What is the CO of a SCT?

I haven't measured the scope's Strehl, but I know what views good optics produce. Over the past 17 years, I have had 7 Astrophysics apos (92 mm f/4.9 to 180 mm f/9), 1 AP 10" f/14.6 Mak-Cass (CO ~ 23%), and 2 Zeiss APQs. Each of these scopes perform as expected, given their design, producer's reputation, and aperture (and I've critically compared them to other scopes of simliar aperture, e.g., SCTs). I'm sure you'll have something disparaging to say about each of these instruments, given the experience you have with your own instruments, but the crushing weight of many others' experience with these scopes will argue heavily against you.

If you have any other OT statements, contact me via PM.

Edited by JJK (12/05/13 09:13 AM)


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rmollise
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Reged: 07/06/07

Re: Why do people even buy SCTs??? new [Re: TheObserver]
      #6234973 - 12/05/13 09:37 AM

Quote:

the last time someone showed up with sct to our meet up. first he had 2 horses helping him to pull that carriage . and by the time he setup and started observing we were having pizza. i would never consider buying something that big and heavy. i setup in 30seconds




Ah...I see that after only 12 pages of this stuff we have, in true CN fashion, reached the reductio ad absurdum stage!


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seawolfe
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Reged: 06/26/13

Loc: N 47.11.23 W 122.20.18
Re: Why do people even buy SCTs??? new [Re: TheObserver]
      #6235003 - 12/05/13 09:48 AM

Quote:

the last time someone showed up with sct to our meet up. first he had 2 horses helping him to pull that carriage . and by the time he setup and started observing we were having pizza. i would never consider buying something that big and heavy. i setup in 30seconds




I'm not so sure.... I have an AVX Edge HD and the set up time is about the same as my friend's Orion XX12g truss Dob.

True, his alignment is only 2 stars whereas mine is 2+4 for a nice ASAP for viewing. For spot on polar alignment, it takes more time and effort.

As for horses carrying the heavy load... well, his monster heavy Dob outdoes mine in the weight to carry arena. Good grief, his base unit alone weighs almost more than my whole setup.

But there again, his is a 12 inch as mine is a lightweight 8 inch.


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Footbag
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Re: Why do people even buy SCTs??? new [Re: TheObserver]
      #6235022 - 12/05/13 10:00 AM

Quote:

the last time someone showed up with sct to our meet up. first he had 2 horses helping him to pull that carriage . and by the time he setup and started observing we were having pizza. i would never consider buying something that big and heavy. i setup in 30seconds




The CPC's are alt-az. Setup is as simple as it could be. 30s is about right.


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Mark Costello
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Re: Why do people even buy SCTs??? new [Re: TheObserver]
      #6235056 - 12/05/13 10:18 AM

That SCT rig must have been a whopper with all the trimmings. If I were to get one, it'd be in the range of 8-10" and probably closer to 8" (maybe "nine and a quarter"). How long would it take to set one of those on an AVX mount, including all the orientation work? My set up time including all accessories (chair, notebook, charts, etc.) is about six minutes which I find acceptable. For a larger one, a setup time of 15 minutes would be OK since it would be used for longer weekend sessions (Saturday Night Special ).

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David PavlichAdministrator
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Reged: 05/18/05

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Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6235114 - 12/05/13 10:45 AM

Quote:

Quote:

the last time someone showed up with sct to our meet up. first he had 2 horses helping him to pull that carriage . and by the time he setup and started observing we were having pizza. i would never consider buying something that big and heavy. i setup in 30seconds




Ah...I see that after only 12 pages of this stuff we have, in true CN fashion, reached the reductio ad absurdum stage!




Good one!

David


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roadi
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Re: Why do people even buy SCTs??? new [Re: Eddgie]
      #6235158 - 12/05/13 11:10 AM

"Why do people even buy SCTs???"

Affordable for most, reasonable quality
Nothing wrong with SCT, only some manufactures QC but this might have changed.


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Doug Culbertson
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Reged: 01/06/05

Re: Why do people even buy SCTs??? new [Re: rmollise]
      #6235159 - 12/05/13 11:11 AM

Quote:

Quote:

the last time someone showed up with sct to our meet up. first he had 2 horses helping him to pull that carriage . and by the time he setup and started observing we were having pizza. i would never consider buying something that big and heavy. i setup in 30seconds




Ah...I see that after only 12 pages of this stuff we have, in true CN fashion, reached the reductio ad absurdum stage!




Sorry, but I went to FSU. Is that Latin for Horse Hockey? If so, I agree.


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TheObserver
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Reged: 09/24/13

Loc: Light Polluted, NY
Re: Why do people even buy SCTs??? new [Re: Doug Culbertson]
      #6235223 - 12/05/13 11:44 AM

Quote:

Quote:

Quote:

the last time someone showed up with sct to our meet up. first he had 2 horses helping him to pull that carriage . and by the time he setup and started observing we were having pizza. i would never consider buying something that big and heavy. i setup in 30seconds




Ah...I see that after only 12 pages of this stuff we have, in true CN fashion, reached the reductio ad absurdum stage!




Sorry, but I went to FSU. Is that Latin for Horse Hockey? If so, I agree.




SCT known to start house fire dont believe me check this out http://goo.gl/C33wxK


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: roadi]
      #6235243 - 12/05/13 11:52 AM

Quote:

"Why do people even buy SCTs???"


Nothing wrong with SCT, only some manufactures QC but this might have changed.




about a 38 percent central obstruction cannot be named as "nothing wrong", especially for visual instrument...


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drago
sage


Reged: 01/11/08

Loc: Latvia
Re: Why do people even buy SCTs??? new [Re: JJK]