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Equipment Discussions >> Cats & Casses

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shawnhar
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Loc: Knoxville, TN
Re: Why do people even buy SCTs??? new [Re: GeneT]
      #6241583 - 12/08/13 09:06 PM

The real answer to the OP's question is this.
The same reason people buy Honda Civics.
It does mostly the same things a Hummer or Ferrari will do, at a fraction of the cost and it's easy to handle.


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DesertRat
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Re: Why do people even buy SCTs??? new [Re: shawnhar]
      #6241675 - 12/08/13 09:51 PM

Bill wrote:
Quote:

Scopes are like mates. There is no set of discrete universal qualities that make one person better than another for a mate. It's all personal based on the individual's likes and dislikes.


Where I live the law limits me to one wife. Thats a good thing usually.

One scope - never!

Brian has a convincing argument above for a refractor and a SCT. Nice choices btw. And for the Dob people, yes those have a place as well.

Is it really surpising a maknut likes Maks and a frachead likes refractors? I like em all. So lets dispense with this silliness unless you really want to milk this thing to the new year!

Glenn


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Jon Isaacs
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Re: Why do people even buy SCTs??? new [Re: shawnhar]
      #6242826 - 12/09/13 02:49 PM

Quote:

The real answer to the OP's question is this.
The same reason people buy Honda Civics.
It does mostly the same things a Hummer or Ferrari will do, at a fraction of the cost and it's easy to handle.




Many people buy Honda Civics because they do the things a car needs to do better than either a Hummer or a Ferrari does them... more reliable, more comfortable, more efficient...

Not sure the same is true with SCTs.

Jon

Jon


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shawnhar
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Re: Why do people even buy SCTs??? new [Re: Jon Isaacs]
      #6243101 - 12/09/13 04:47 PM

Quote:

Quote:

The real answer to the OP's question is this.
The same reason people buy Honda Civics.
It does mostly the same things a Hummer or Ferrari will do, at a fraction of the cost and it's easy to handle.




Many people buy Honda Civics because they do the things a car needs to do better than either a Hummer or a Ferrari does them... more reliable, more comfortable, more efficient...

Not sure the same is true with SCTs.

Jon

Jon



I was thinking of the Hummer as a 20" Dob and the Ferrari as a 7" APO.
Our club has a 20" Dob and a 5" refractor, both I have gotten to setup/teardown and use, the refractor quite a bit.
In my opinion an 8 or 10" SCT is more comfortable and efficient, easier to handle, versatility is better, lots of aftermarket add-ons, plentiful on the used market.
It seems unlikely that many folks who could afford the Ferrari get a Civic instead because it "hold's groceries" better. Aston Martin makes a fine grocery carrier, it's called the DB9.
Just sayin, the SCT on an EQ mount does everything I want it to do at a very reasonable price. Most of the time I can view the eyepiece sitting in a recliner, it tracks, can take pictures, screw in a focal reducer, piggyback an 80mm APO, it's short so doesn't need a mondo expensive mount, If I broke the glass I could replace the entire OTA for 500 bucks.
Seems "Civicy" to me...


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gmartin02
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Re: Why do people even buy SCTs??? new [Re: Daniel Mounsey]
      #6243123 - 12/09/13 04:57 PM

Quote:

Ed,
In my opinion, the SCT design is generally soft, but good enough for the average consumer. Most observers do not have the observational experience or seeing conditions conducive enough to appreciating the difference between SCT's and world class Newtonians, apos and Maks. I'm sure if more observers spent some time viewing with some really world class optics in the right seeing locations, they'd have an awakening. That is not to say there hasn't been a few really good SCT's out there.




Unfortunately (for some others reading this post), I have to agree with Daniel.

A couple of years ago I purchased a lightly used C11. I enjoyed it for the 6 months I owned it. It was really nice having that much aperture on a GOTO mount. I live in Southern California where the seeing is usually well above average compared to many parts of the country, and we don't have the extreme temperature differentials at night that many other places have that lead to bad SCT cooling issues.

Why did I sell it? Because the images were just a little too "soft" at high powers (above 150x) for my tastes. When I got the C11 it was slightly out of collimation so I re-collimated the secondary and the star test was concentric after doing this, but it was still a little too soft for my tastes (even after a full 3 hour cool down). I don't have this "softness" issue with my 6" Intes MK-67 Deluxe, even at 300x (once it eventually cools down, which takes at least as long to cool as the C11 did). Again, the C11 was really good up to 150x, it was only beyond that where it began to break down.

Anyway, I ended up trading the C11 for a 12.5" Dob with a Lightholder primary and a Protostar ULS Quartz secondary. After cooling down, the images in the 12.5" Dob above 150x are significantly better to what the C11 showed. Although I miss the GOTO convenience of the C11 on a GEM, I prefer the images in the Dob.

Perhaps I just got unlucky and my sample of the C11 was one of the "mediocre ones".

Note: The above applies to visual only.

If I had more astro funds, I probably would have kept the C11 for planetary imaging and eventual HyperStar use. I still may pick up another C11 or EDGE 11 one of these years for the same. I think the SCT type scopes are really well set up for planetary imaging, which is why so many people use them for that purpose.

Final note: I think it is completely silly for anyone to use stacked AP planetary images as an example of how well a scope could perform visually. This is like comparing apples and oranges. I would never think of using my 8" RC or my 8" imaging Newtonian for regular visual use, but both work very well as AP scopes. (I did use both visually when I first got them just too see what the view was like through an eyepiece: not spectacular).


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BKBrown
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Re: Why do people even buy SCTs??? new [Re: gmartin02]
      #6243205 - 12/09/13 05:42 PM

Quote:

Final note: I think it is completely silly for anyone to use stacked AP planetary images as an example of how well a scope could perform visually. This is like comparing apples and oranges. I would never think of using my 8" RC or my 8" imaging Newtonian for regular visual use, but both work very well as AP scopes. (I did use both visually when I first got them just too see what the view was like through an eyepiece: not spectacular).




You are correct in saying that this is like comparing apples and oranges. Since I believe I am the only person to post planetary images in this thread, I can say definitively that nobody did that here Greg. Please show me where the OP limited his question to visual only use...I must have missed that part. This thread, according to the OP, asked (in a very tongue-in-cheek manner) "Why do people even buy SCTs???" My answer: because they are superb planetary imaging platforms that are so good in that role that they are used by a great many people for that purpose - including many (perhaps most) of the finest amateur planetary imagers in the world. I would ask in return, why don't these same folks choose to use refractors, Newts, Mak Newts, DKs, RCs or whatever instead?

Clear Skies,
Brian

Edited by BKBrown (12/09/13 07:04 PM)


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TG
Pooh-Bah


Reged: 11/02/06

Loc: Latitude 47
Re: Why do people even buy SCTs??? new [Re: Daniel Mounsey]
      #6243313 - 12/09/13 06:39 PM

Quote:

Ed,
In my opinion, the SCT design is generally soft, but good enough for the average consumer. Most observers do not have the observational experience or seeing conditions conducive enough to appreciating the difference between SCT's and world class Newtonians, apos and Maks. I'm sure if more observers spent some time viewing with some really world class optics in the right seeing locations, they'd have an awakening. That is not to say there hasn't been a few really good SCT's out there.




There's nothing wrong with the SCT design. It can be designed to give practically perfect Strehl in visual wavelengths. It can also be designed to give a small 20-25% CO, just like any cassegrain. I wonder if people singing praises of DKs realize that the SCT is also effectively a DK with the corrector+spherical primary acting like the ellipsoidal primary of a DK.

My suspicion is that it's mainly not falling temperatures which are the bugaboo of SCT users at northern latitudes but differential cooling between the sky side and the ground side of the OTA. I solved it by installing Ed's TEMPest fans and wrapping the entire OTA in Reflectix to prevent it from forming tube currents. Last night, the tube had cooled to ambient 18F (verified with an IR thermometer), and yet, turning on the TEMPest fans made a difference as seen in the star patterns of Castor. Without the fans, there'd be multiple 'lobes' coming and going so much that the airy disk was barely visible. With the fans on, the airy disk appeared. Normally, I'd have attributed this to bad seeing but in fact, seeing was just a tad north of average.

In such conditions, Jupiter at 330x provided very nice detail including several ovals and 2 giant bluish festoons.

In fact, I'm sure I caught a glimpse of the pup in the C11HD. It came and went but Sirius was boiling. I had a much better view in much better seeing in the AP178 a few days back. Sadly, I was too pooped to exchange scopes to see what would show in the C11HD.

Tanveer.


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Jon Isaacs
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Re: Why do people even buy SCTs??? new [Re: shawnhar]
      #6243340 - 12/09/13 06:50 PM

Quote:


I was thinking of the Hummer as a 20" Dob and the Ferrari as a 7" APO.
Our club has a 20" Dob and a 5" refractor, both I have gotten to setup/teardown and use, the refractor quite a bit.
In my opinion an 8 or 10" SCT is more comfortable and efficient, easier to handle, versatility is better, lots of aftermarket add-ons, plentiful on the used market.




Comparing a 20 inch Dob to an 8 or 10 inch SCT doesn't make much sense to me. Outside of the fact that they both have similar focal lengths, they are very different scopes.

My own experience has been comparing 8-10 inch SCTs with 10 inch Dobs, 12 inch SCTs with 12.5 inch Dobs.. Dobs in these sizes are sit down scopes and easy to setup and quite very capable... faster cooling, wider fields of view, etc. etc... If I wanted to compare an SCT to my 16 inch or 25 inch Dob, I would pick one of similar aperture...

Honda Civic's: The people I know that can easily afford fancy cars generally drive Honda's, Toyata's, stuff like that. As transportation, they are just a better tool.

Jon


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gmartin02
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Re: Why do people even buy SCTs??? new [Re: BKBrown]
      #6243362 - 12/09/13 06:58 PM

Hi Brian,

I misread your intention about the posted Jupiter images, becasue both of the posted quotes in your response with the Jupiter images mention looking through a telescope, and did not mention imaging with a telescope:

"...looked through an AP 10..."

"...any can look throught its clear aperture without CO..."

Sorry about that. I just re-read it again, and you definitely did not say anything about visual (I inferred that becasue of the original quoted references). I wasn't thinking of the OPs original question - just your response and the quotes contained in your response.

Quote:

I would ask in return, why don't these same folks choose to use refractors, Newts, Mak Newts, DKs, RCs or whatever instead?




That is a really good question. Obviously large SCTs make extremely good planetary imaging scopes.

Here are my "uneducated guesses" for why the other scope types do not show up more for superb planetary images:

Refractor - Lower resolution for planetary (at least in the sizes affordable by amateur astronomers) and small "native" image scale.

Large Newts (12"+) - Much harder/more expensive to mount than a SCT, although I did find a site by a guy in Australia that takes some decent planetary images with a Newt: http://www.acquerra.com.au/astro/

DKs & RCs - Price - there is no reason that a large (12"+) DK or RC would not make an outstanding planetary imaging scopes, but most of those scopes are really pricy - perhaps triple the price of a C14, or way more than triple the price of a C11.

Conclusion about my guesses: I think many or most use large SCTs for superior planetary imaging becasue they appear to have the best performance/price ratio for this purpose, and are easier to mount than some of the other large scope types.


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Vondragonnoggin
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Loc: Southern CA, USA
Re: Why do people even buy SCTs??? new [Re: BKBrown]
      #6243364 - 12/09/13 06:59 PM

Quote:

Quote:

Final note: I think it is completely silly for anyone to use stacked AP planetary images as an example of how well a scope could perform visually. This is like comparing apples and oranges. I would never think of using my 8" RC or my 8" imaging Newtonian for regular visual use, but both work very well as AP scopes. (I did use both visually when I first got them just too see what the view was like through an eyepiece: not spectacular).




You are correct in saying that this is like comparing apples and oranges. Since I believe I am the only person to post planetary images in this thread, I can say definitively that nobody did that here Greg. Please show me where the OP limited his question to visual only use...I must have missed that part. This thread, according to the OP, asked (in a very tongue-in-cheek manner) "Why do people even buy SCTs???" My answer: because they are superb planetary imaging platforms that are so good at that role that they are used by a great many people for that purpose - including many (perhaps most) of the finest amateur planetary imagers in the world. I would ask in return, why don't these same folks choose to use refractors, Newts, Mak Newts, DKs, RCs or whatever instead?

Clear Skies,
Brian




Brian, I dont know what most others are thinking from the pictures, but the first thing I thought of wasn't the images themselves, but the representation of what an SCT can be useful for. Imaging with a large aperture rig in a relatively compact setup.

also, generally speaking, the practicality of having an 11' or 14" design in a compact scope. Visually or photographically, SCT's accomodate the large aperture crowds with a versatile design.


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BKBrown
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Re: Why do people even buy SCTs??? new [Re: gmartin02]
      #6243468 - 12/09/13 07:45 PM

Quote:

Hi Brian,

I misread your intention about the posted Jupiter images, becasue both of the posted quotes in your response with the Jupiter images mention looking through a telescope, and did not mention imaging with a telescope:

"...looked through an AP 10..."

"...any can look throught its clear aperture without CO..."

Sorry about that. I just re-read it again, and you definitely did not say anything about visual (I inferred that becasue of the original quoted references). I wasn't thinking of the OPs original question - just your response and the quotes contained in your response.

Quote:

I would ask in return, why don't these same folks choose to use refractors, Newts, Mak Newts, DKs, RCs or whatever instead?




That is a really good question. Obviously large SCTs make extremely good planetary imaging scopes.

Here are my "uneducated guesses" for why the other scope types do not show up more for superb planetary images:

Refractor - Lower resolution for planetary (at least in the sizes affordable by amateur astronomers) and small "native" image scale.

Large Newts (12"+) - Much harder/more expensive to mount than a SCT, although I did find a site by a guy in Australia that takes some decent planetary images with a Newt: http://www.acquerra.com.au/astro/

DKs & RCs - Price - there is no reason that a large (12"+) DK or RC would not make an outstanding planetary imaging scopes, but most of those scopes are really pricy - perhaps triple the price of a C14, or way more than triple the price of a C11.

Conclusion about my guesses: I think many or most use large SCTs for superior planetary imaging becasue they appear to have the best performance/price ratio for this purpose, and are easier to mount than some of the other large scope types.




No worries Greg! This thread has gone on so long that it's getting hard to keep track of who said what. The two quotes from above ("...looked through an AP 10...","...any can look through its clear aperture without CO...") are from someone else's response, I didn't write them.
You made several good observations in response to my return question. Short answer: SCTs provide large, affordable, solid quality aperture for planetary imaging applications. They are easy to mount, provide a broad range of imaging options and accessories, are easily collimated to the necessary standard (most amatuer observers do not typically bother to collimate to planetary imaging standards) and are comfortable to use operationally. Apo refractor images can be very nice, but few of us can afford 10" to 12" Apos (and the observatory facilities they require), and the 4" to 6" OTAs within reach of the average guys wallet do not provide the light gathering capability and resolution to provide the results most of us in this line are looking for (think Damian Peach). Ditto cost-wise for the high end DKs and RCs (and how about the COs there?). Big Newts have the disadvantage of being large and cumbersome, difficult (and expensive) to mount, and you have not one but two mirrors to collimate to planetary imaging standards...but many folks use them. Anthony "Bird" Wesley from Australia, discoverer of two Jupiter impact events, is one of our Newt using practitioners (he occasionally chimes in over on the Solar System Imaging forum) and he clearly does super work from his permanent site...there are many others. So it comes down to cost and efficiencies for most of us, and SCTs are proven performers in the planetary imaging arena.

Clear Skies,
Brian

Edited by BKBrown (12/10/13 08:19 AM)


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azure1961p
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Re: Why do people even buy SCTs??? *DELETED* new [Re: BKBrown]
      #6243496 - 12/09/13 07:56 PM

Post deleted by azure1961p

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azure1961p
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Re: Why do people even buy SCTs??? new [Re: BKBrown]
      #6243497 - 12/09/13 07:56 PM

I liked the photo comparisons to instruments a lot actually. And of course no CCD image or even, drawing, can truly show the visual experience - its really unto itself. I can't say Ive ever had to study a mars drawing by another astronomer for 40 minutes trying to convince myself a feature was present.

The CCD images were a fine thing and served their purpose well.

Nice work Brian.

Pete


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EFT
Vendor - Deep Space Products
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Re: Why do people even buy SCTs??? new [Re: azure1961p]
      #6243527 - 12/09/13 08:16 PM

Quote:

I liked the photo comparisons to instruments a lot actually. And of course no CCD image or even, drawing, can truly show the visual experience - its really unto itself. I can't say Ive ever had to study a mars drawing by another astronomer for 40 minutes trying to convince myself a feature was present.

The CCD images were a fine thing and served their purpose well.

Nice work Brian.

Peye




While the planetary images are not the perfect analog for the visual experience, they are the best objective comparison that we have gotten in this thread. All other comparisons, particularly for visual experiences, are clearly subjective and can easily vary from viewer to viewer, even if the views are very unbiased in their observations.


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vahe
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Reged: 08/27/05

Loc: Houston, Texas
Re: Why do people even buy SCTs??? new [Re: TG]
      #6243633 - 12/09/13 09:09 PM

Quote:


There's nothing wrong with the SCT design. It can be designed to give practically perfect Strehl in visual wavelengths. It can also be designed to give a small 20-25% CO, just like any cassegrain.





Indeed;
http://www.cloudynights.com/item.php?item_id=77

Vahe


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BKBrown
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Reged: 08/23/09

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Re: Why do people even buy SCTs??? new [Re: azure1961p]
      #6243695 - 12/09/13 09:37 PM

Quote:

I liked the photo comparisons to instruments a lot actually. And of course no CCD image or even, drawing, can truly show the visual experience - its really unto itself. I can't say Ive ever had to study a mars drawing by another astronomer for 40 minutes trying to convince myself a feature was present.

The CCD images were a fine thing and served their purpose well.

Nice work Brian.

Pete




Thanks Pete

Clear Skies,
Brian


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tclehman1969
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Re: Why do people even buy SCTs??? new [Re: BKBrown]
      #6243741 - 12/09/13 10:02 PM

There are many reasons for buying an SCT. Just as there are many reasons to purchase a refractor or a Newtonian. For my needs, an 8" SCT with a drive system allowed for aperture, compactness, economic factors and ease of portability the other two didn't. Not knocking the other systems, just what works for me. But, I also have an 80mm refractor, too, a real nice one. But it's 80mm. I wanted a refractor for some of what I do and an 80mm was my budget limit.

I suppose if there were no cost, transportation or any other restrictions, I could just get a Hubble!


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Dan McConaughy
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Reged: 11/11/06

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Re: Why do people even buy SCTs??? new [Re: tclehman1969]
      #6243851 - 12/09/13 11:12 PM

I had an 8" D&G refractor, and it did not perform visually as well as my C14 on the planets, not to mention DSOs. The C14 was easier to use, too. Well made SCTs are hard to beat when it comes to performance per dollar. Refractors are hard to beat when it comes to dollar per performance.

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mmalik
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Re: Why do people even buy SCTs??? new [Re: Dan McConaughy]
      #6243921 - 12/10/13 12:11 AM

Given NOT so precise optics of SCTs, they are more suited for visual wavelengths; given SOMEWHAT precise optics of refractors, they are more suited for photographic wavelengths. Regards

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Live_Steam_Mad
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Reged: 07/24/07

Loc: Moss Bank, St.Helens, England
Re: Why do people even buy SCTs??? new [Re: mmalik]
      #6243954 - 12/10/13 12:43 AM

Oh if only every SCT had very smooth optics, proper attention to stray light in the blackening / baffling, recirculating cooling (doubling as a carry handle), and very very low astigmatism, very low coma, and very low Spherical Aberration, around 33 per cent obstruction, and was coma free / flat field corrected.

Takahashi should restart their 9" SCT production but the one thing I disliked about that one was being not able to see the whole of the Pleiades in the FOV of any eyepiece without vignetting (apparently, so I read, if I remember right) since it was F12, whereas the C9.25" F10 can fully illuminate a 41mm Panoptic (46mm field stop) and show all the Seven Sisters properly, via the 46mm internal diameter baffle tube (even if the 36 per cent CO is a bit large I feel). I'd actually prefer Tak to go to 34 per cent CO and F10 to enable this. I wonder what baffle internal diameter the Tak SCT has? Anyone know? Was the TSC 225 primary baffle tube a little small, in order to accomodate it's 28 per cent CO (mirror) / 33 per cent CO (secondary baffle obstruction)?

Another related one - it bugs me that e.g. the TEC 8" Mak Cass can't do the whole Pleiades either even at F11 due to the 0.75 degrees field maximum (30mm field stop illuminated properly, max) without vignetting, so I read. I don't understand why that field is so small? Something about the Mak design I suppose? Wheras the 8" SCT at F10 seems to be able to show the 7 sisters with ease with 2" TV 55mm Plossl etc. due to the 38mm field stop being illuminated properly in the SCT at F10 due to the primary baffle tube having 38mm inside diameter.

I have always loved the SCT design and when I read the Telescope Optics book by Rutten & Venrooij it always strikes me as to what a marvel and how versatile the F10 optimised SCT can be when properly designed and made with 100 per cent quality control.

It's such a pity that some of the Celestron and Meade SCT's that I see interferogram reports of seem to be so bad (rough optics, astigmatic, a ton of spherical aberration), it's a terrible shame that those 2 companies have the cheek to put them onto the market with optics like that (the price is "cheap", but even so...). One article in the December 1989 issue of Astronomy magazine USA always stuck in my mind of when they tested the Meade 10" SCT ;-

https://plus.google.com/photos/101932667412801910198/albums/59243873149200618...

...and from looking at those interferogram reports I see, I see that it doesn't matter whether you have an orange tube SCT from 1974 or a year 2013 Edge 11", you can still get some real mediocre optics / lemons, which always puts me off buying new, I just can't trust Meade or Celestron to make consistently excellent SCT's

I have a second hand C11 OTA with no serial number on it (maybe ex-CG11, some of those we the same) that I bought from a Chris in Skelmersdale a few miles away in 2006 and I paid 900 GBP, the secondary mirror has a patch on it with just a little cloudiness but when I saw the Star Test at 186x (he had no higher magnification eyepieces in his collection when I looked in his ep. case) I was astounded as it was utterly identical on either side of focus in rock steady seeing, I could hardly believe me eyes when I saw it. The pattern was so clear, I could see no roughness either. But I saw that star test a long time ago now and I ran out of money for a mount and have been using a friend's 8" ACF for the last 3 years and am only now saving up for a mount since he just moved down south and I am now left with my 4" frac as my only 'scope with a mount. I hope to goodness my C11 is good on the planets when I get the new mount for it.

The ACF was rather good on Jupiter, but I haven't had a lot to compare it with unfotunately. I am also now starting to try and regroup my local Astronomical Society (they split up 10 years ago so I was told recently by the "secretary") and maybe get a look through their 'scopes. I love testing and comparing 'scopes almost more than observing LOL. I would always buy any SCT second hand and do a high power Star Test before handing over money for one.

Regards from NW England,

Alistair G.

Edited by Live_Steam_Mad (12/10/13 01:26 AM)


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