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Modern CAT Optical Advances

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#1 TCW

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Posted 05 November 2013 - 03:46 PM

More than 25 years ago I had the chance to view through a C14 (my dream scope) at Glacier Point under dark skies in a side by side comparison with my Cave Astrola 12.5 inch F6 and was profoundly disappointed in every regard. Although this occurred far too long ago to remember specifics, what I do remember is that contrast, sharpness and brightness were all inferior to my Newtonian. In conversing with the C14 owner I found that he agreed.

Now that there have been so many advances optically and electronically I find myself being drawn back towards investing in a large CAT like a Celestron 14 inch or a Meade 14 or 16 inch due to the portability and the GOTO mounts.

What I am wondering is will I see an improvement over the old Celestron or will the Newtonian still beat out the newer designs with it's smaller central obstruction and simpler optics?

#2 Bruce FitzGerald

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Posted 05 November 2013 - 04:56 PM

More than 25 years ago I had the chance to view through a C14 (my dream scope) at Glacier Point under dark skies in a side by side comparison with my Cave Astrola 12.5 inch F6 and was profoundly disappointed in every regard. Although this occurred far too long ago to remember specifics, what I do remember is that contrast, sharpness and brightness were all inferior to my Newtonian. In conversing with the C14 owner I found that he agreed.

Now that there have been so many advances optically and electronically I find myself being drawn back towards investing in a large CAT like a Celestron 14 inch or a Meade 14 or 16 inch due to the portability and the GOTO mounts.

What I am wondering is will I see an improvement over the old Celestron or will the Newtonian still beat out the newer designs with it's smaller central obstruction and simpler optics?



I think this is just like the which is better, Ford or Chevrolet argument. Optics are most certainly better but if you are looking for portability, a C14 or Meade 16 in scope isn't it. As for the "Large Central Obstruction" here's two photo's taken last spring with my C-14. Judge for yourself.

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#3 Bruce FitzGerald

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Posted 05 November 2013 - 04:59 PM

A more difficult target...M33

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#4 TCW

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Posted 05 November 2013 - 05:39 PM

I don't really see it as Ford/Chevy unless you are talking Meade/Celestron. My interest is primarily visual but may in the future be interested in the astro-photography field. As far as portability I am thinking a C14 is going to be a lot more portable than a 6.5 foot tube that weighs close to a hundred pounds alone.

What I am hoping to find out is if the quality/design of SCT has improved markedly over the last 30 years.

Your photos are beautiful.

#5 vahe

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Posted 05 November 2013 - 05:40 PM

Now that there have been so many advances optically



Specifically what optical advances are you referring to besides QA?

Vahe

#6 TCW

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Posted 05 November 2013 - 05:53 PM

Not sure what QA(quality assurance?) is but the EdgeHD Optics and the use of Ritchey-Chrétien design plus (perhaps) improved quality. I don't know if the old C14's had inferior quality optics or if my experience was a true comparison between the two different designs.

#7 markdaleanderson

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Posted 05 November 2013 - 06:05 PM

I purchased the Nexstar 8SE last summer as my new grab-and-go scope. I spent an entire night doing a side by side with my Zhumell 10 inch Dob. I was stunned at how well the 8SE kept up with the Z10. I'm 85% through the Herschel 400 with the Z10 and did a side by side with a refigured Zambuto 10 inch so I know I have a good mirror in the Zhumell. The Zhumell bested the 8SE by a hair on really dim objects; otherwise, the 8SE gave a comparable view. I would assume the larger CATS would be of the same quality.

Mark

#8 herrointment

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Posted 05 November 2013 - 06:14 PM

The quality, such as it is, may be more consistent today than in the past.

It is what it is....a compromise. I like the two I own.

#9 MikeBOKC

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Posted 05 November 2013 - 06:15 PM

I think it is safe to say that in 25 years SCT optics have been upgraded considerably, when you factor in advances like the ACF and Edge designs. No SCT can diminish the minimal but still real larger central obstruction issue but I think you can approach a potential C-14 purchase with assurance that it will bring you a very high quality large aperture scope equal to or better than a somewhat smaller Newt.

#10 Jared

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Posted 05 November 2013 - 07:50 PM

The consistency of optical quality is generally acknowledged to be better now than 25 years ago in the Celestron SCT's. The coatings have also been improved. Other than that, the C14 is the same scope as it was--same central obstruction, same basic design.

It's hard to know whether you would again be disappointed in a C14 as you were all those years ago at Glacier Point. What was wrong with the last scope you looked through? Was it just out of collimation? Was it a poor quality example? Had it not yet reached thermal equilibrium?

In general, I would expect the brightness of a C14 to be slightly better than in a 12.5" Newt at the same magnification, but the difference is only about 10% once you account for light loss from the larger central obstruction and scatter/reflection from the additional optical elements and diagonal. Not enough to matter much, frankly--just enough that you would be able to tell in a side by side comparison.

As far as resolution, the C14 would be better, so it would be the better choice for planetary photography (especially since it won't have diffraction spikes), but the actual contrast delivered to the eye at mid-frequencies is almost identical--actually slightly favors the 12.5" Newt, but not enough to matter.

Basically, if both scopes are fully equilibrated, of similar optical quality, and both collimated properly there should be a lot more similarities at the eyepiece than differences. If you choose an Edge version of a C14 you would eliminate coma from your view, but adding a paracor to the Newt can accomplish the same thing. I wouldn't choose one over the other for differences in the view. I would look at other factors--such as whether I wanted goto, whether I thought planetary photography was in my future, what budget I had available, etc.. I'd be surprised if either scope materially outperformed the other visually.

Keep in mind that calling a C14 or Meade 14 a "portable" scope is a bit of a stretch. They are more portable than a comparable Newtonian on an equatorial mount, but much less portable than the same aperture scope on a Dobsonian mount.

#11 David Pavlich

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Posted 05 November 2013 - 08:34 PM

The big change from 25 years ago would be the coatings on the corrector plate as Jared pointed out. Light transmission is better. If I go back to visual, there will be a C14 or and M14 in my obs.

David

#12 Bruce FitzGerald

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Posted 05 November 2013 - 09:14 PM

I don't really see it as Ford/Chevy unless you are talking Meade/Celestron. My interest is primarily visual but may in the future be interested in the astro-photography field. As far as portability I am thinking a C14 is going to be a lot more portable than a 6.5 foot tube that weighs close to a hundred pounds alone.

What I am hoping to find out is if the quality/design of SCT has improved markedly over the last 30 years.

Your photos are beautiful.


By Ford vs Chevy I mean that the SCT has matured and improved to a high degree. That Cave Astrola was truly a magnificent scope but the new 14 inch SCT is every bit it's equal. The OTA for my C-14 weighs 100 pounds by itself with the added focuser and an 120mm finder so, it's a push also when you compare the difficulty of lugging that Astrola's optical tube under your arm. That CAT is not light but, as you can see from the unretouched photo's it does give a pretty good image!
So, whether you choose a an SCT, Ritchey-Chretien, Newt, or Refractor there won't be quite as much distance between them as there was 30 years ago. It's more a matter of what you want to contend with in terms of size and weight. My second telescope was a Cave Astrola 8 inch and I do wish I had that scope now but my C-14 will take better pictures!

#13 Glen A W

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Posted 05 November 2013 - 09:31 PM

I used to have a C-14 and never was very pleased with the images, but it was mostly a matter of seeing when viewing the planets, and collimation... A 10.4-inch Vixen Cat I have now is superior on the planets so I sold the C-14. The long focal length of the 14 was the main thing which turned me off. I would say it is actually plenty portable, if you have a helper and you like collimating and are good at it.

I note the 10 inch you compared to was not too short by Newtonian standards, and that would help out a little compared to run of the mill Chinese dobs we see these days which are f/4-5 - which often give great views, nonetheless. The Newt you used was a premium instrument, so it's no surprise it was a winner.

I do believe the current prices on new C-14s are a bargain and you should get one ASAP if it's what you want. They are actually great scopes, but there are a lot of ins and outs to whether you really want to deal with the size, weight, focal length, cooling, collimation, dangerous counterweights (don't ask) and all the rest that comes with a monster like that. GW

#14 orion61

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Posted 05 November 2013 - 10:06 PM

More than 25 years ago I had the chance to view through a C14 (my dream scope) at Glacier Point under dark skies in a side by side comparison with my Cave Astrola 12.5 inch F6 and was profoundly disappointed in every regard. Although this occurred far too long ago to remember specifics, what I do remember is that contrast, sharpness and brightness were all inferior to my Newtonian. In conversing with the C14 owner I found that he agreed.

Now that there have been so many advances optically and electronically I find myself being drawn back towards investing in a large CAT like a Celestron 14 inch or a Meade 14 or 16 inch due to the portability and the GOTO mounts.

What I am wondering is will I see an improvement over the old Celestron or will the Newtonian still beat out the newer designs with it's smaller central obstruction and simpler optics?


One thing many people miss when people start comparing optics and views when the 2 scopes are not at the same place, and worse when time is involved. you are judging against a fond memory.

#15 TCW

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Posted 06 November 2013 - 04:14 PM

Actually this comparison was 10' feet apart and simultaneous. The C14 owner agreed that the C14 optics were inferior and had known about it since he bought it. You are right about the fond memories part!

#16 frolinmod

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Posted 07 November 2013 - 01:43 AM

If fond memories ruled the day I'd be looking for an RV-6.

#17 Gil V

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Posted 07 November 2013 - 12:32 PM

I think production processes are certainly better than they were 20 or 30 years ago, how could they NOT be?

That being said, there is no reason that an older CAT couldn't be diffraction-limited. I would expect it to be less common, as there had to be greater variation in older polishing methods than in methods being used today.

#18 jhayes_tucson

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Posted 07 November 2013 - 12:57 PM

More than 25 years ago I had the chance to view through a C14 (my dream scope) at Glacier Point under dark skies in a side by side comparison with my Cave Astrola 12.5 inch F6 and was profoundly disappointed in every regard. Although this occurred far too long ago to remember specifics, what I do remember is that contrast, sharpness and brightness were all inferior to my Newtonian. In conversing with the C14 owner I found that he agreed.

Now that there have been so many advances optically and electronically I find myself being drawn back towards investing in a large CAT like a Celestron 14 inch or a Meade 14 or 16 inch due to the portability and the GOTO mounts.

What I am wondering is will I see an improvement over the old Celestron or will the Newtonian still beat out the newer designs with it's smaller central obstruction and simpler optics?


Interestingly enough I had a similar impression when I first examined both the Meade and Celestron products back in the 1970's. I was working for an expert witness for Celestron as a part of their patent dispute back then and my assignment was to evaluate both telescopes. At the time, neither telescope struck me as presenting an image as sharp and "pleasing" as my old f/6.7 Newtonian. In hindsight, I think that the problem is that it is hard to compare an f/11, 14" telescope directly to a 12", f/6 Newtonian. You need to match exit pupils, FOV, eyepiece quality, thermal stability and that's hard to do given the basic optical parameters. The difference in obscuration ratio will have virtually no discernible effect on visual performance--particularly for stars. Even on planets, it would be very difficult to demonstrate much of a difference due solely to obscuration ratio.

I recently acquired a 10 year old 14" (non-HD) Celestron and I've been very impressed with it's performance. It is definitely more sensitive to seeing effects compared to any smaller scope. It also takes a while for it to come to thermal equilibrium, but overall, the imaging performance is quite good. In addition, the Celestron f/7 focal reducer works surprisingly well for visual use providing a FOV of nearly a degree with a 36 mm, wide field eyepiece. The off-axis optical performance really starts to fall off once you get more than about 15 arc-min off axis, but for visual work, it's not all that noticeable. I've attached a photo I took of NGC 7331 with the f/7 reducer to show the star quality at the edge of the field. With my camera, the field is almost exactly 30 arc-min edge-to-edge. I had some vingetting and I didn't subtract flats so it isn't a great photo, but it does show that the image quality isn't that terrible at the edge of the field.

I bought the telescope used and I'm having a blast with it. If that keeps up, I may trade up to an HD OTA and a more modern mount at some point. Bottom line: You only live once so go for it and buy the 14". I think that you might like it as much as I do.

John

PS Be aware that the 14" is moveable, but not what I would call "easily portable". It just weighs too much and there are too many parts. Just hoisting the OTA up and getting it secured onto the mount dovetail by myself is a challenging (and somewhat risky) job. To address that issue, I have the whole thing mounted on a massive roll-able pier. As a "roll-out" observatory, it only takes 10 minutes to get it outside, aligned and ready go.

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#19 jjack's

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Posted 07 November 2013 - 05:51 PM

If i'll need a big movable scope for visual only, this one have the best ratio portability/cost/power: Dobson Orion SkyQuest XX14 Goto.
Far Better than a 14" SCT.
But ymmv

#20 jhayes_tucson

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Posted 07 November 2013 - 10:44 PM

I have a small Orion DOB, but frankly I can't stand the alt-az mount. Trying to track anything near the zenith is a pain and looking at anything at high power is brief at best. They are certainly portable and I know a lot of you guys love 'em; but they aren't for everyone. I can probably have my roll out C14 set up and aligned nearly as fast as any DOB of a similar size. I will certainly concede that the DOB clearly wins if you want to toss it in the back of a car and head out to a dark site.
John

#21 TCW

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Posted 08 November 2013 - 09:06 PM

Great Post!






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