Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Apos better than Newts?

ATM reflector refractor
This topic has been archived. This means that you cannot reply to this topic.
407 replies to this topic

#26 GShaffer

GShaffer

    Knight of Ni

  • *****
  • Moderators
  • Posts: 6,831
  • Joined: 28 Feb 2009

Posted 28 April 2015 - 10:48 AM

 

 

But where today would you purchase a reflector like this one I bought in Japan in 1988?

Parallax comes to mind. 

 

 

Clear skies!
Thomas, Denmark

 

 

Was thinking the same thing myself Thomas....... I have a 10" f/5 newt that was built by Parallax using a .998 Strehl mirror by Ed Stevens. I don't have any way to validate that claimed figure in the paperwork other than to say I use its build quality and  performance as a benchmark to compare my other scopes and for that matter any other scope I have looked thru.......I have yet to see it outclassed either in construction or performance........While I have no doubt scopes that can outclass it do exist, I am unlikely to run up on one.......


 

#27 Talsian

Talsian

    Vostok 1

  • -----
  • Posts: 155
  • Joined: 22 May 2013

Posted 28 April 2015 - 11:06 AM

It is too bad about the RA.  Perhaps you should find a program that does dictation so that you can flesh out your ideas.  As is, there is not much to which to respond, in this newt vs apo comparison.


 

#28 pga7602

pga7602

    Viking 1

  • *****
  • Posts: 969
  • Joined: 11 Jun 2009

Posted 28 April 2015 - 11:41 AM

Ed, I think this may help you.  You will need to download the google chrome browser and go to this website https://dictation.io/

 

Click the start dictation button on the lower left and a pop up will appear asking if the website has permission to use your microphone.  Simply start talking and a sentence will appear.  If you say "full stop" a period will appear.  When you are done, simply copy the text and paste it anywhere you like. 


 

#29 areyoukiddingme

areyoukiddingme

    Fly Me to the Moon

  • *****
  • Posts: 5,040
  • Joined: 18 Nov 2012

Posted 28 April 2015 - 12:37 PM

Ed, I think this may help you.  You will need to download the google chrome browser and go to this website https://dictation.io/

 

Click the start dictation button on the lower left and a pop up will appear asking if the website has permission to use your microphone.  Simply start talking and a sentence will appear.  If you say "full stop" a period will appear.  When you are done, simply copy the text and paste it anywhere you like. 

 

Holy crap. It works. And I have a really weird accent!


 

#30 Stephen Kennedy

Stephen Kennedy

    Surveyor 1

  • *****
  • Posts: 1,938
  • Joined: 03 Jul 2014

Posted 28 April 2015 - 12:39 PM

 

 

 

 

 

The problem is it is impossible to find a Newtonian OTA of that quality today.  ......... just get stuck in Dobsonians..........

Sure you can.  There are several thoughtful and very skilled structure makers out there who will build a scope to your specifications and build it around the highest-end mirrors available which are as good or better than any mirrors made in the past.    Cost you some $$$, though.  (But still far cheaper than the equivalent sized APO....) 

 

And the mount type - Dob or GEM - has very little to do with the optical quality at the eyepiece.  It may have a little something to do with the holistic viewing experience, sure. (Seated? eyepiece position? etc.)   I'm not sure you should knock Dobs across the board like that....

 

Times are good for Newtonian telescope buyers!!

 

Dave

 

But where today would you purchase a reflector like this one I bought in Japan in 1988?

 

http://imgur.com/sjSpFIn

http://i.imgur.com/HKRxYGu.jpg

 

Unlike Ed, I did not make this telescope other than determining the best combination of GEM and OTA.

 

The mount is a Pentax MS-5 GEM and the OTA is a Mikage 210 mm F/7 Newtonian.  The OTA weighs 22 kg and the GEM 140 kg.  Together they cost me 750,000 yen ( about $6,400 at current exchange rates).  I will concede that there has been some inflation in prices since 1988 so something similar would cost more than $6,400 now.

 

I grant you that a scope such as yours is no longer available as a branded, buy-it-in-a-store product.  The quality level of your scope, both optically and mechanically, can be equalled by combining the best mirrors from certain suppliers and structures from certain others.  

 

I suspect a 7 or 8-inch, f/8 Zambuto mirror in a Teeter or JPAstrocraft structure with all the bells and whistles - ServoCat, boundary layer fans, optical flat mirror holder etc. would set you back at least $6400.  But it would be at least as good an instrument.

 

Dave

 

No Dobsonian , even Teeter, Webster or JPAshcroft, could ever match the strength, rigidity and tracking precision of the Pentax MS-5 GEM.  There is a reason why professional astronomers use mounts made out of steel rather than wood.


 

#31 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 84,024
  • Joined: 16 Jun 2004

Posted 28 April 2015 - 12:52 PM

 

No Dobsonian , even Teeter, Webster or JPAshcroft, could ever match the strength, rigidity and tracking precision of the Pentax MS-5 GEM.  There is a reason why professional astronomers use mounts made out of steel rather than wood.

 

There are also good reasons why professional astronomers use truss scopes on ALT-AZ mounts with apertures far larger than 8 inches or so... The modern scientific telescope looks a lot more like a truss dob with a servo cat than it does an equatorial mounted Newtonian...  

 

There are lots of nice telescopes and mounts out there... each of us chooses based on our observing styles and preferences.. Personally, I like generous amount of aperture in an easily transported, portable scope that can be manually tracked at high magnifications.  There is really only one way to spell a scope like that, it's called a Dobsonian.  Add in a 4 inch apo with a short focal length and a flat field of view and I am pretty much set.

 

Something to think about anyway... 

 

The


 

#32 pga7602

pga7602

    Viking 1

  • *****
  • Posts: 969
  • Joined: 11 Jun 2009

Posted 28 April 2015 - 01:57 PM

 

Ed, I think this may help you.  You will need to download the google chrome browser and go to this website https://dictation.io/

 

Click the start dictation button on the lower left and a pop up will appear asking if the website has permission to use your microphone.  Simply start talking and a sentence will appear.  If you say "full stop" a period will appear.  When you are done, simply copy the text and paste it anywhere you like. 

 

Holy crap. It works. And I have a really weird accent!

 

You can't thank all those people that use google voice as their main phone.  Google has been recording accents since the start of that project, so the system is now smart enough to recognize most common accents :)

 

Back on topic.. I agree with Jon, most scientific instruments look more like trust systems than close tube mounted on an EQ.  They look more like truss dobs on Alt Az.  BTW, there's no rule that a dob has to be made out of wood :p


 

#33 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • Posts: 12,924
  • Joined: 05 Oct 2008

Posted 28 April 2015 - 02:38 PM

 

Apos have a farfegnugen which no other telescope type can match.

They have a what? I had to look that up. It sounds almost like a lethal, asian disease or something.

 

But if you spell it correctly, it's fahrvergn├╝gen, which is German for "travelling pleasure" (or actually, "pleasure while travelling"), which makes a lot more sense. 

 

And I'll have to agree. 

 

 

Clear skies!

Thomas, Denmark


 

#34 macdonjh

macdonjh

    Fly Me to the Moon

  • *****
  • Posts: 5,427
  • Joined: 06 Mar 2006

Posted 28 April 2015 - 03:21 PM

APO refractors are clearly superior to any other telescope design for all the reasons stated in all the refractor forums around the world.  Perfect color correction, unobstructed aperture for maximum resolution, no collimation issues, fast cool down, great for photography, perfect ..., ideal ..., peerless...


 

#35 macdonjh

macdonjh

    Fly Me to the Moon

  • *****
  • Posts: 5,427
  • Joined: 06 Mar 2006

Posted 28 April 2015 - 03:24 PM

APO refractors are clearly superior to any other telescope design for all the reasons stated in all the refractor forums around the world.  Perfect color correction, unobstructed aperture for maximum resolution, no collimation issues, fast cool down, great for photography, perfect ..., ideal ..., peerless...

 

That guy's a fool.  Newtonian reflectors are clearly superior to any other telescope design ever tried for all the reasons stated in any forum anywhere in the world.  No color at all to be corrected, real aperture making real resolution possible, simple collimation, open Newtonians will cool faster than any refractor, photography at f/4 vs. photography at f/7?  Fuhgeddaboudit!  Perfect..., ideal..., peerless...


 

#36 macdonjh

macdonjh

    Fly Me to the Moon

  • *****
  • Posts: 5,427
  • Joined: 06 Mar 2006

Posted 28 April 2015 - 03:25 PM

 

APO refractors are clearly superior to any other telescope design for all the reasons stated in all the refractor forums around the world.  Perfect color correction, unobstructed aperture for maximum resolution, no collimation issues, fast cool down, great for photography, perfect ..., ideal ..., peerless...

 

That guy's a fool.  Newtonian reflectors are clearly superior to any other telescope design ever tried for all the reasons stated in any forum anywhere in the world.  No color at all to be corrected, real aperture making real resolution possible, simple collimation, open Newtonians will cool faster than any refractor, photography at f/4 vs. photography at f/7?  Fuhgeddaboudit!  Perfect..., ideal..., peerless...

 

 

:)


 

#37 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 23,946
  • Joined: 22 Feb 2010

Posted 28 April 2015 - 03:25 PM

Apos have a farfegnugen which no other telescope type can match.

 

funnypost.gif


 

#38 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 23,946
  • Joined: 22 Feb 2010

Posted 28 April 2015 - 03:32 PM

I think all telescopes are great.

 

refractors

 

newts [even this pink one https://www.youtube....h?v=Peep673_3ZI ]

 

dobs

 

maks

 

unobstructed dobs

 

sct...wait...ok I like almost all telescopes...you can keep the sct's. :p


Edited by Pinbout, 28 April 2015 - 03:39 PM.

 

#39 Galicapernistein

Galicapernistein

    Viking 1

  • *****
  • Posts: 591
  • Joined: 24 Sep 2007

Posted 28 April 2015 - 09:37 PM

Provided that the f ratio was high enough and the secondary was small enough, I don't see any reason why a reflector couldn't perform as well as or better than a smaller f ratio APO refractor, and nearly equal a similar f ratio refractor. A faster reflector will lose out because of its large secondary, but aside from lacking a secondary, what optical advantage comes from focusing light through a lens as opposed to reflecting it from a mirror?
 

#40 george golitzin

george golitzin

    Surveyor 1

  • *****
  • Posts: 1,942
  • Joined: 24 Feb 2006

Posted 28 April 2015 - 11:30 PM

Are apos better than Newts?

 

No.

 

If I want a killer view of a planet, it's going to be in a newt of 12.5 inches or larger.  Pretty hard to pony up the cash for that size apo.

 

If I want detail on DSOs, it's going to be in a newt of 16 inches or larger.  The larger the better.  They don't make apos that big.

 

What's left?  Pretty wide-field views of deep sky?  A 6-inch f/5 newt with coma corrector does the trick.

 

So why would I care to compare apos and newts of equal aperture?  An academic interest?  The only pertinent question is, what instrument are you going to use for this or that application?

 

Apos?  Why bother?  


Edited by george golitzin, 28 April 2015 - 11:34 PM.

 

#41 Glen A W

Glen A W

    Surveyor 1

  • -----
  • Posts: 1,767
  • Joined: 04 Jul 2008

Posted 29 April 2015 - 12:44 AM

 

Apos?  Why bother?  

 

 

It's status, plain and simple!  Show up at a star party with an AP or Takahashi, especially of 5 inches or more, and people will line up to see M13 looking badly because the telescope is not big enough to show the stars in globulars well.  Two kinds of people think money can beat physics.  People getting face lifts and some backyard astronomers.

 

Those apos are very nice scopes.  I love them and have one.  But there is something perverse going on with peoples' desires for them.....

 

Glen


Edited by Glen A W, 29 April 2015 - 12:48 AM.

 

#42 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • Posts: 12,924
  • Joined: 05 Oct 2008

Posted 29 April 2015 - 04:22 AM

Well, here's my take on it:

 

Newtonians CAN deliver extremely good performance, but you can't buy an off the shelf unit that does (to my knowledge). All the economy ones have serious design flaws that limit their performance, most notably in thermal issues. No fans, too tight tubes, thick mirrors, etc. Equatorial mounted ones have no rotating rings and undersized mounts, too tall piers or tripods, etc. 

 

On the other hand, off the shelf apochromats often deliver close to their theoretical performance right out of the box. This creates a real-world situation in which a 4" ED is often very close in actual planetary performance to a 8" newtonian and often beat a 6" quite clearly, at least in the first couple of hours of observing and most people often only have a few hours early in the evening and have no option for letting the reflector cool down first. Under these circumstances, a newtonian is at a severe disadvantage to a refractor, despite the theoretically better performance. 

 

If the observer is not aware of the many potential issues of the newtonian, and let's be honest here, very few observers are, then the newtonian is very often not performing as well as it can, while the small apochromat nearby is running at close to full potential. I've seen this in practice a lot at star parties and during my own comparisons. 

 

An example: I have a 6" f/8 Sky-Watcher newtonian with a 1.25" secondary. It has very good optics. Not perfect, but very good. But the tube is too narrow, 7" in diameter, and too short. It's also metal. And black. It rapidly undercools and this creates a lot of tube currents. The tube is too short, so that warm air from my breath flows in through the light path. Wrapping it in a blanket and extending the tube with a SCT dewcap helps tremendously, but not completely. The cell is too tight, so there's no room for air to move around it and adding a fan to the rear of the scope has no benefits. 

 

Once it is cooled and properly insulated, the optics shine and it outperforms my 85mm Zeiss very easily. But the 85mm has shown better images for at least the first hour and a half by that time and for many people, depending on the time of the year, by then it's often time to go to bed. 

 

So, does the situation HAVE to be this way? No, but if I want to change it, I *must* build my own scope, since there's NO ONE building a properly designed and manufactured, off the shelf 6" f/8 newtonian for a reasonable amount of money. And building scopes is not for everyone. Most don't even have the option.

 

In my opinion, the newtonian is a completely misunderstood scope. People want it to be cheap, because it can be, so they demand the lowest cost possible and buy very cheaply made scopes, but the design actually have so many potential issues, that you HAVE to spend some real money and attention to it, to get a properly working scope, at least when we're talking planetary observing. And when you take the time to adress the issues, you suddenly end up with a scope that is not so cheap any more. 

 

It really is strange. People spend lots of money on refractors and maksutovs. Those are considered high-end designs. The newtonian is capable of running neck to neck with them, but is not considered a high-end design, so people don't want to spend money on it.  

 

 

Clear skies!

Thomas, Denmark 


 

#43 Herr Ointment

Herr Ointment

    Cosmos

  • *****
  • Posts: 9,798
  • Joined: 12 Mar 2011

Posted 29 April 2015 - 04:53 AM

The ATM built 8" f/8.5 Newtonian that I purchased is my best planetary scope without question.

 

It's not easy to use but it is worth the effort.

 

And it can get better if I'd only get off my duff and help it along.

 

$250.00 w/mount.


 

#44 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 84,024
  • Joined: 16 Jun 2004

Posted 29 April 2015 - 04:55 AM

Provided that the f ratio was high enough and the secondary was small enough, I don't see any reason why a reflector couldn't perform as well as or better than a smaller f ratio APO refractor, and nearly equal a similar f ratio refractor. A faster reflector will lose out because of its large secondary, but aside from lacking a secondary, what optical advantage comes from focusing light through a lens as opposed to reflecting it from a mirror?

 

Refractive optics are more efficient than reflective optics and have less scatter. In smaller apertures, using a small secondary to achieve that high contrast planetary perfermance limits the size of fully illuminated field of view.

 

 A 6 inch F/8 refractor can have a large fully illuminated field without compromising the planetary contrast...

 

When I look at the two designs, refractors and reflectors, what I see is that in the smaller apertures, the high efficiency and lack of a central obstruction give refractors a significant advantage. But as aperture increases, color correction becomes increasingly difficult, the scopes become impossibly long because focal ratios increase all the while the disadvantages of the Newtonian lessen with increased aperture.

 

The size of the secondary is related to the field stop of a wide field eyepiece which is a constant so a reasonably well illuminated 42mm field stop in a 6 inch might require a 30% or larger CO, in a 12.5 inch it can be done with a 20% CO and in a 25 inch one as small as 15%.  Fast focal ratio Newtonians are as robust  at large apertures as at small and the loss of efficiency is not as important..

 

So.. To my eye the equation looks like this... Small scopes are best if they are refractors, large scopes are best if they are reflectors... I think the marketplace pretty much supports this ascertation.

 

Jon


 

#45 auriga

auriga

    Surveyor 1

  • -----
  • Posts: 1,537
  • Joined: 02 Mar 2006

Posted 29 April 2015 - 07:13 AM

In my mind, the virtue of the apochromatic refractor is not its ability to provide excellent planetary views nor its ability to provide excellent low power, wide field views but rather its ability to do both in the same instrument without the need for compromising either. A smaller Newtonian can be optimized for one or the other but not both.

 

If one is looking for the best possible planetary views, it makes no sense to me to consider it as a competition, the best 6 inch Newtonian versus the best 6 inch refractor, both are ultimately limited by their relatively small apertues.. This in not a yacht race where one has to abide by a set of artificial rules, this is simply open class observing where one is free to pit a 12.5 inch Newtonian against a 6 inch refractor or an 8 inch whatever..

 

Me, I'll take a smaller apo for it's versatility and efficiency and a larger Newtonian for its greater capabilities. My scopes are not competitors, they're companions..

 

Jon

Yes, Jon,  you have hit the nail on the head as usual.

Why compare Newts and Apos of equal aperture? Why not compare Newts and  Apos of equal cost, or of equal weight or equal bulk or equal portability?

 

As   you imply, equal aperture doesn't even mean equally wide maximum field of view. It may imply equal resolution or equal light-gathering  power, but in view of the differences in cost, weight, bulk, portability and ergonomics, one could easily get a Newt with more resolution and more light gathering power by simply increasing the aperture.

 

For example my 11" Newt gives far better resolution and brightness on globular clusters than does a 5" Apo and is far less expensive. But a 5"Apo would  be far better for wide field photography.

 

In my opinion, the comparison of equal aperture is arbitrary and is unrelated to  usability, affordability, or ergonomics, except for maximum field of view, where the refractor is better and therefore more suited to wide field imaging. But everyone already knows this.

 

If one wants   to exceed a 6" Apo in resolution,  a 10" or larger Newt with a premium mirror  will do the job and have more light gathering power in addition. No need for a specialized 6" f/11 Newt.

 

 

Bill


 

#46 dag55

dag55

    Viking 1

  • *****
  • Posts: 660
  • Joined: 13 Apr 2011

Posted 29 April 2015 - 08:31 AM

I agree, to compare equal aperture isn't a full comparison. For instance I am building a 8" f-7.5 Zambuto 1.52" 19% 1/18 wave sec. mirror scope with six point flotation cell, insulated, with active cooling and boundary-laminar air layer removal. I wouldn't expect it to best or equal an 8" APO, but I would expect it to best any 6" APO and come close to a 7" APO for far less cost and ease of mount used as it will weigh in at about 30lbs. which is far less than an 8" or 7" APO would. With the reflective coatings of the two mirrors losing 12% to 16% using enhanced coatings+ secondary mirror size over the more efficient throughput of the APO one needs to compare a Newt. of at least one inch more aperture to get close to an equal performance level. The 8" I am building has a illuminated field of about 70% over a 32mm field. This scope should be a great planetary and dso scope which is my WMR scope, Working Mans Refractor.
As Jon stated small reflectors vrs. small refractors the refractors win, but at 8" things begin to change, I may build a 10" or 12.5" inch later but for the Midwest region I live in 8" will suffice, not to mention I have one of those terrible Dobs. 17.5" that I built, and wood is a very good material for use as it is very stable and if built to tight tolerances does the required job very well.
Dane
 

#47 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 23,946
  • Joined: 22 Feb 2010

Posted 29 April 2015 - 08:46 AM

 

For instance I am building a 8" f-7.5 Zambuto 1.52" 19% 1/18 wave sec. mirror scope with six point flotation cell, insulated, with active cooling and boundary-laminar air layer removal. I wouldn't expect it to best or equal an 8" APO

 

That's only because he undercorrects his mirrors.  :grin:

 

actually I heard from someone who attends stellafane, he looked thru several cz primary scopes and all were undercorrected and wouldn't even make the cut in the optics competition.

 

I'd better hone my skills before I enter one of my mirrors.


 

#48 precaud

precaud

    Fly Me to the Moon

  • *****
  • Posts: 5,009
  • Joined: 05 Dec 2012

Posted 29 April 2015 - 09:19 AM

 

Apos?  Why bother?  

 

Show up at a star party with an AP or Takahashi, especially of 5 inches or more, and people will line up to see M13 looking badly because the telescope is not big enough to show the stars in globulars well.

 

+1. Even inexperienced observers can tell the difference. When someone brings a frac to a local outreach event, as the evening progresses, the lines form at the newts, dobs, and sct's...


 

#49 bsavoie

bsavoie

    Viking 1

  • *****
  • Posts: 616
  • Joined: 30 Nov 2013

Posted 29 April 2015 - 10:38 AM

I like the idea of equipment improvement, and finding efficiency in numbers. I currently have 26 telescopes, with my biggest being a 17.5 inch f/6 Dobsonian with wheel barrow lift. I am always on a ladder, so I have a good fiberglass three legged 10 foot ladder that collapses down to 6 ft.

 

Explore Scientific is currently marketing an ulta-light Dob in Europe, and the rummer is that next year it will be made available in the USA. Unlike my 17.5 inch built by Ross Workman with a mirror by Terry Ostahoski, the ES is only 90 pounds. I am 69 years old, so it seems good that I wait and save my money. I don't think a dob will meet my AP desires, and that is a bridge I will also need to cross.. 

 

Perhaps it is not good to come to any conclusions.. but to just keep learning, buying, growing, and exploring, both equipment and sky.

 

Bill


 

#50 dag55

dag55

    Viking 1

  • *****
  • Posts: 660
  • Joined: 13 Apr 2011

Posted 29 April 2015 - 11:15 AM

I think maybe the statement," can Newts. be as good as refractors",  would be appropriate, I like refractors very much, as I have had some nice ones TV  Genesis SDF 101, Tak. FS 128, SW 120ED and even an old Meade 127 ED f-9 that was surprisingly good. I would say the TV SDF101 I should have kept for the wide fov but the others always left me wanting for more aperture.

If I had no lack of funds then a 8" Tec. or APM would be mounted in a permanent observatory on my northern field about 1/4 mile from my house. But since I am not in the top income bracket of even the middle class hence Newtonian on an EQ mount with rotating rings is an affordable solution for good quality views and ease of use at a price point that makes sense. I have kept the telescope heard to a minimum to keep cost down and I like quality over quantity, so a 17.5 quality DOB. with servocat and argo navis and a 8" Newt. on a G-11. My grandson has a small Orion 80mmED for our refractor wide field views so until the urge to build another Newt. gets me accumulating components I will be content with what I have.  Contentment is of great gain as a wise man once said.

Dane :)


 


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics