Celestron C9.25-S GT Schmidt-Cassegrain w/XLT Coatings Good Buy?

Question

I am in the middle of upgrading telescopes. Right now I have a Meade ETX-80at which isn't what I hoped for. In the near furture I want to do astrophotography with my 35mm or even a DSLR when I have the money. I have done extensive research on which scope I want and I think this is the one I want. Any imput/advice would be awesome!

Answer 1

I use the Celestron 9.25” SCT w/XLT coatings for DSO astrophotography and have had fairly good results.
I initially bought the AS-GT scope/mount combo and was just blown away with the goto accuracy. I used a SAC7 CCD camera and found that the mount was not up to the task of unguided long exposure imaging.

Phase Two, I bought a Hutech modified Canon 300D DSLR and built a side by side mounting bracket for my 9.25” SCT and a Celestron 102mm f/5 refractor. I used the SAC7 as a guide camera and the 300D for imaging. I could now do 5 minute guided exposures through the SCT and got much better results. The SAC7 and C102 guided well using “Guide Dog” guiding software. The mount was still not all that I would have hoped for. The total weight of the two scopes and cameras was around 33lbs. This was too much weight for imaging as vibrations slowed too slowly and even a slight wind would ruin a frame. Guiding is also somewhat problematical. There is a great deal of backlash in the gear train, and there is about 50 arc/sec periodic error, often with steep curves.

Phase Three, While the AS-GT mount was a very nice light weight goto mount well suited to visual observing, it lacked the accuracy needed for long exposure astrophotography. While I can’t say enough about the mount as visual mount, and even for astrophotography when used for short focal length, wide field imaging (500mm or so), it just isn’t up to snuff for the 2350mm (or 1480mm at f/6.3) of the 9.25” SCT. I therefore bought a used Losmandy G-11 mount with the Gemini goto. This mount is AWSOME! Pointing accuracy is spot on, there is very little backlash and the periodic error is less than 15 arc/sec even before the PEC. With this setup I could guide an exposure as long as I liked.

Phase Four, I bought a used Sbig ST8-XE camera and really started imaging! I’m currently imaging with the ST8-XE through the 9.25” SCT on my Losmandy G-11. You can see
some of my images on my web page

www.budgetastro.com/web

and here

http://antwrp.gsfc.nasa.gov/apod/ap070405.html

Conclusions: The Celestron 9.25” SCT is a very good mass produced SCT. It is the only SCT that I know of that uses a parabolic primary mirror. Most use a spherical primary and rely on the corrector plate to remove the spherical aberrations. It does like most SCT’s (but not all) have a moving primary mirror as the focusing mechanism. This is not the best for astrophotography as the mirror will shift slightly. This can be relieved by using a rear cell Crawford focuser like I do. Also these scopes come in two flavors, aluminum tube and carbon fiber tube. I have the aluminum tube and it suffers from shrinkage due to temperature changes much worse than the carbon fiber model. If you plan on astrophotography it is very convenient not to have to refocus for every 5 or 6 degrees of temp. change.

The AS-GT mount is great for visual but leaves a lot to be desired as an imaging platform. For the price it’s hard to beat, but it is only really good for short focal length astrophotography.

A fork mounted Celestron scope despite the higher price in no better as an imaging platform than the AS-GT mounts. This goes for the Meade LX200 series mounts as well.

The Losmandy G-11, wow, this is a performer! Solid tripod, heavey EQ head, good payload (65lbs), and the Gemini goto is just awsome. There is a lighter version called the GM-8 that is also quite good, but if you are in the hobby for the long haul, get the G-11, you will never regret it.

The SAC7 CCD, not much of an imager, but a great autoguider.

Canon Digital Rebel, good for the brighter DSO’s (10mag or brighter). Has a huge image sensor and one shot color is easy to process. It has however only a 12 bit A/D converter, and is not too good at narrow band imaging.

Sbig ST8-XE, any self guided Sbig camera is just a joy to image with. Good sensitivity, TEC cooling for dark noise reduction, second ccd for self guiding, whats not to love.

Answer 2

It's a very good visual scope. If you want to do deep sky astrophotography, plan on spending many more thousands for an autoguiding system, new drive and a few thousand for a good CCD.

Answer 3

the size of that scope is good, although what you really want is a good equitorial mount to track objects properly. depending on what type of photography you want to do, if you plan on taking images of galaxies, a good tracking mount is essential. i take pics with a DSLR and they come out amazing...no need for an expensive ccd camera. if you are just planning on taking pics of bright objects like planets or even just constellation pics the c9.25 is a good scope. but if you want to do some deep sky work, research a good mount!!! good luck!!!!!