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Astronomy by Michelle

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Astronomy Product Reviews by Michelle Stone

The C11 OTA

Manufacturer: Celestron
Web Site:??????


bullet 11" (279mm) Aperture
bullet Focal Length of 2800mm
bullet Focal Ratio of f/10

The decision to purchase

I had purchased a Losmandy G11 mount earlier the year before to try my hand at some astrophography. I used the mount with a C8 and Vixen 102mm Flourite for the photo tests and they had turned out fine. Based on the success of these shots at my small ranch in the Sierra, I decided to build an observatory there.? I also made up my mind (even though I did not like SCT's all that well) to pick up a C11 when I could get a good deal on a used one. I believed that the scope would be a fine observatory instrument.

I hadn't planned on finding a good deal for some time. But it wasn't a month or two later when I saw a C11 OTA advertised on the net. It took a bit to negotiate the deal (especially since the seller was in Canada) but everything worked out great.


I have used both a C8 and an 18" Obsession extensively. Both of these instruments have a focal length of about 2000mm.? I must admit that it took me a night or two to mentally adjust for the 2800mm focal length of the C11.? The C11 takes a larger eyepiece to get to my standard viewing magnification of 100 diameters. Since I don't have a 28mm eyepiece, I use a 19mm Panoptic. This gives me a magnification of 147 diameters. In my observatory, I have the C11 mounted side by side with the Vixen 102mm flourite refractor.? The Vixen provides the wider field views and the C11 provides the narrow views. It is a terrific and very complementary combination.? This set up is a pleasure to use.

Unlike my C8 (with average optics), my C11 tube has very good optics. Defocussed star tests show amazing results from edge to edge. The rings are textbook.? The defocussed images remain circular from edge to edge of the field with no distortions (common among 8" SCT's). The first night that I set up the C11, I was only able to perform a quick star test on the optics and snatch a quick view of Saturn.? Weather prevented me from doing much more. Saturn was crisp and the features were very well defined.? I was a happy camper, even though I had only 5 minutes of viewing.? The scope would not be set up again for another 2 months until the Observatory was finished.

First Light (for real)

The first real use of the scope was when I opened my observatory for the first time on December 25, 1997. The night was very cold and the seeing was not all that good, but the scope was a delight to use. I had purchased and installed Kendrick dew heaters. Since this was a permanent installation, this seemed like a good idea.? It was a very good idea! With a cold night and some humidity, the dew shield failed within the first 30 minutes. I turned on the Kendrick heaters and was soon back to viewing within just a few minutes. I used my new telescope all night, revisiting old companions, and searching for new ones. As I mentioned before, the new focal length, took a little to get used to. But there was something that I did not expect. As I looked at objects, even though they were a bit dimmer than in my large scope, the detail still seemed to be there. I soon came to realize that I might not be brining up the 18" to the observatory much more.? I'm not saying that the images were better in the 11, but that they were very good.? And that in the dark sky of my observation site, in most cases, those images of the C11 would satisfy my needs.? For photography, I am sure they will be stupendeous.


I love the C11 OTA on the Losmandy G11 mount.? The mount is rugged and beefy enough to carry it and a good sized refractor in a saddle mount.? Mounting anything heavy on the top of the scope makes it more difficult to balance.? I have looked at the Ultima mounting of the C11 and determined that it is not for me.? I am first of all biased against fork mounts due to the vibration dampening problems.? The Ultima mount is clearly made to be portable.? It is light weight and it shakes and vibrates with the slightest bump.

The scope is a delight to use and I would venture to say that the optics on the 11 inch scopes from Celestron are quite good.? Since these scopes are for more serious observers, I think that the manufacturer does a more careful job at getting them right.? The scope makes a great observatory installation.? I believe it to be a bit cumbersome as a portable scope, due only to the fact that the Losmandy GEM mount and tripod take some time to set up.
My Obsession 18" actually is more portable since it is so easy to set up and collimate.

So, if you are a techno weenie like me, you'll probably get one.?