Should I consider an SCT ;-)?

Well, before I take the Dobs plunge, I was looking at the Legault's web site again (eg. Alpine Valley). While there, those pictures through his 12" Meade SCT impressed me greatly as they look very high contrast and has high sharpness.
http://perso.club-internet.fr/legault/

I realized the question has been asked about SCT vs refractor. But what about 8" SCT such as Celestron/Meade vs 8" Dobs such as Discovery PDHQ? Perhpas the central obstruction and contrast degradation is a myth; for if it weren't, how then could these pictures be so contrasty and sharp? As you can see, I've never looked through an SCT. I'm looking for an 8" for visual use only. Also, having a driven mount is nudgingly superior ;-). I won't need
the NO-GO ;-) BTW. I need the 8" for light polluted DSO observing (dark sky trip some times) and want superb planetary/lunar city observing.

Celestron seems to have a new SCT called the "Advanced Series" touted to be hand figured which made me drooling just reading about it!
http://www.astronomics.com/main/product.asp?tog=2&n1=2&t1=4&styp=3&vid=4&product%5Ftype%5Fid=1&sku=ASC8&bURL=tCelestron%2Easp&mystype=Schmidt%2DCassegrains

What do you guys think? Am I being a sucker :-( if I go with an SCT?

Thanks,
Ron B[ee]
PS My TV-102 will be my primary scope and the SCT/Dobs will reside in my garage ;-).

Hi Ron,
Sure, but you should go look through a few 8" SCTs and see for yourself. Make sure the samples you look through is well collimated and properly cooled down. You saw the thread on SAA about 8"SCT vs 8" dob. I guess neither side convinced you.

For me the choice is easy. I don't like newtonians because of the eyepiece location. Period. I like refractors and all cassegrain variants because I like to be behind the end of the OTA, not up front beside it. Just a personal preference, like some people love hot spicy foods and some don't. Do you care where the eyepiece is located?

There are many good SCTs out there and there are many bad ones, too. I have a Meade 10" SCT on a CI700 mount. I recently bought Bob's knob for it and collimate the heck out of my SCT on a night of good seeing (8/10) and was rewarded with a jaw dropping view of Jupiter at 313x. There was the GRS, white clouds, barges, festoons, you name it. I had to come inside and look for a picture/diagram that shows what all these things are called so I can write them down in my log. The image was bright, sharp, and there was plenty of contrast. I've had only one other night this winter when the seeing was almost as good. That night, I could only only go up to 208x on Jupiter. My jaws still dropped, thought. I considered myself lucky because I think I got a good one.

A few months back I had a chance to look at Saturn through one of the new Nextstar 11GPS. It really surprised me. I didn't know such contrast was possible in an SCT. It has better contrast than mine! (Don't you hate it when that happens?) A friend of mine has a Celestron Ultima 8" that he raves about when it comes to planetary performance. This is from a guy who owns about 10 APO refractors and as many SCTs. (He did very well during the stock market boom and bought telescopes instead of a Boxster). He tells me to keep an eye out for an Ultima 8 if I want to increase my chances of getting a really good 8" SCT.

I don't think it's a question of whether SCTs are any good, but where can you get a good one. If you choose an SCT, find out if you like fork mounts or not. And by the way, I think Celestron always said their optics is "hand-figured". Other posters, please correctly me if I'm wrong.

Regards,

Nat C.
Santa Fe, NM
PS The garage is a good place to keep SCT during the winter. It helps with cool down time.
PPS Love your Light Cup observing reports.

hi,

I have a Televue Genesis SDF and a Celestron 8" SCT. The two compliment each other nicely.

The key to performance in the SCT is proper cool down and critical collimation ( collimating on a star at 600x ).

The 4" is great for wide feild views and quick looks and the 8" is much better on DSOs. On nights with good seeing the 8" is better on the planets and moon, the 4' is better in poor seeing.

Having said that, the SCT with the reputation for the very best optics is the Celestron 9 1/4 OTA. It is said to offer more contrast than the others.


clear skies,


Larry Citro

www.starryforge.com

I would urge caution when using photos through a 12" SCT to attempt to guess visual performance from an 8" SCT. There's nothing like actually using one yourself to determine if it's right for you. I don't know if every single SCT from 8" through 12" that I've looked through has been a bad example, or out of collimation, or what. But personally, I've just not been terribly impressed with the contrast of any of the Meade SCTs that I've looked through, even though some of them were capable of good CCD imaging. That's not to say that any of them were bad scopes. Their owner's were certainly happy with them, but I decided that they just weren't right for me. I think I got spoiled early on with a really top-notch, high contrast 6" Mak, and none of the larger SCTs that I've seen could compete in terms of sheer contrast to either the Mak or the DOBs that I've used. Again, this is just one guy's annecdotal experience and is not necessarily indicative of the breed. Take it with salt, but do try before you buy if at all possible.

Mike Swaim

Get a C11, Meade 12", or Celestron / Meade 14". My 152ED is spectacular on planets. But so is my 12" Meade SCT. The 12" can outdo the 152ED in good seeing by a decent margin on high contrast fine details. Low level is about the same due to the 33% central obstruction. Saturn especially shows up much clearer at 500x or higher in the SCT. I had venus at 600+ one night and saw some surface detail in the 12" SCT.


You can mount the light cup with the SCT and have both handy when observing.

It goes without saying that the 12" is totally superior to the 152ED when it comes to any kind of cluster, galaxy, or dim nebula. They both are examples of some of Meade's best optical work.

"Perhaps the central obstruction and contrast degradation is a myth; for if it weren't, how then could these pictures be so contrasty and sharp?"

I don't know if it's a myth or not. I've never looked through an SCT either. I do know the pictures you are looking at on the web are not sharp. The originals might be, but not the ones you are looking at. Unless you have the freedom to zoom in to view microscopically small detail, your computer screen can not display sharp images, because its resolution is too coarse. With that exception, everything you see on a computer screen is inherently soft, and this can hide a multitude of sins.

To illustrate, the Legault website's most impressive image to my eye, by far, is the image of Saturn, and I think we would all agree it looks like a supurb image. On my screen that image is 4 inches across. I can see the Encke division, which shows that this is a high-resolution image. But I can barely see the Encke division, which shows that this is not a sharp image. A high resolution sharp image of Saturn displayed at that size should make the Encke division stand out much more.

Contrast is another issue. Moon pictures, particularly, almost always display harsh contrast. This is not the same as good contrast. The key is not whether the blacks look really black, and the whites look really white, but whether subtle, nearly identical shades of grey can be distinguished. If they can, especially in the highlight and deep shadow areas, then that's good contrast.

Conveniently, you have an excellent point of reference for both sharpness and good contrast with your TV-102. Just set it up next to someone's SCT on a night of good seeing and you will be able to find out all you need to know about these subjects in a few minutes.

You may also find out that the SCT has virtues that have nothing to do with sharpness and contrast, for which you could excuse some shortcomings in those areas. I'd like to find out more about the Celestron 9.25 myself.

Steve

I have owned two SCT's, a c8 and a 10" meade LX-200 and both have been great. Now I use the 10" LX200 and it provides breathtaking view of the planets and deep sky objects. I don’t know where people get this nonsense that SCT's have bad performance and the central obstruction is WAY overblown by a few refractor maniacs(no offense) running around the message boards. I have nothing against refractors and I own a c102 but in no way is any 4" scope going to outperform a 8" scope. Sorry, do not have any experience with reflectors.

Ron,

I have a few SCT's. Here are my comments:

N5: Neat little scope but images are not up to my 4" TV Genesis in any department.

C9.25: Great scope but a good C11 will easily outperform it. My Genesis cannot keep up with this scope at all. Neither can my 4" f/15 Jaegars. Under certain conditions my excellent 6" Chineese refractor can equal it on the moon.

C11: Great scope; images can be as sharp as a C9.25 but as an added feature it gathers significantly more light. I find the ota easily transportable, virtually no different from the C9.25 in that catagory. The C9.25 is about the same length, by the way. As a matter of complete disclosure, I bought a C11 ota used on Astromart that will not hold collimation. It is now a problem that I will deal with myself or send the scope to Celestron for repair. BTW, collimated the images are excellent IMO. A friend of mine, Ron "Dewbuster" Keating, bought a C11 new from Company 7; it is an outstanding scope that at times practically keeps up with my excellent C14. The larger field of view of the C11 as compared with the C14 gives the C11 a significant advantage when viewing a lot of popular objects.

C14: Great scope but the ota is not as managable as the C11 or C9.25. I can and do handle this scope completely by myself but its not a piece of cake like a C11 ota.

All of these scopes need a G11 or equal. The new Celestron equatorial mounts look interesting. My G11 handles all of these scopes very well.

I would not consider a C8 because the C9.25 and C11 are substantially better IMO, don't cost much more (for a serious observer) and are just as easy to carry around IMO.

Bottom line, I consider the C11 on a G11 the ultimate easy to transport scope.

Ralph