A long, long time ago, in a galaxy that seemed far , far away (1996), , I decided that I might want a telescope. Wasn’t quite sure so I hedged my bet and bought a scope that could also be used as a spotting scope. I bought a Celestron C90, a 90mm Maksutov-Cassegrain design encrusted with “Rubber Armor” .
It came with a tiny 5 x 30 finder (worthless) and a pretty nice 26mm Celestron Plossl eyepiece. First light was Saturn, tiny but the rings were there.
One of the unusual design features of the C90 is its helical focusing. You have to learn how to critically focus it and it does take some time. But I have been a photographer for a long time and the lens like focusing did take that much time to “master”. Eventually I re-greased my C90 with white lithium grease and the focusing became significantly easier.
Someone once told me the C90 wasn’t a “real Telescope”. Well I have to disagree. I have seen 80 of the M Objects and lots of other objects with mine. Here is what I did to mine to make it a better, for me, telescope.
First I replace the little 5 x 30 with a Celestron 6 x 30 LER finder. I was using a computer program to make finder charts and the 6 x 30 worked pretty well. I could see enough stars to find my way to the bright M’s and I could find stuff in day light.
I was in Yellowstone watching the wolves when I realized I need something else as the inverted view was fine for astronomy, but not for birding or wildlife viewing. I started my search and found something that again added functionality to my C90.
I bought one of the very first EZ finders from Orion. It was small and very light. Super glue has held it in place for nearly 14 years. Now this was multi-ring finder, just a red dot. But it quickly got me near where I wanted to be and was bright enough at maximum to use in the daylight.
I think I’ve only used about 3 batteries in the 14 years. Once I learned locations of things like M13, 31, 27 , etc., it just made finding them again so easy.
When I realized that I was getting to really enjoy visual astronomy, I made the single biggest improvement. I got a Large Adopter Ring (LAR) that allowed the C90 to accept real SCT accessories. I then got a Lumicon 1.25 diagonal and a set of Celestron plossl eyepieces and a barlow.
I’ve found that when cooled I can get to about 160X with the C90. I normally use a 32, 20, and 7.3mm as my EP range. When used with Ultimas I’ve gone as high as 180X with good results.
My C90 has been mount on several differet tripods – a set of Manofrotto 3001 legs with fluid head, a GT80 Mount, and now sits on a 055 Carbon Fiber set of legs with a 488 head. This is my quick look setup (I use the tripod with my nikon and longer lenses also). Its light weight and very stable. I normally use this for planets, the Moon, and things like M42 in the winter.
These scopes are very inexpensive on the used market since they are no longer made. If you can find one with Starbright coatings I think they are a very good deal at $150 that they seem to be selling for. This little scope with the few modifications I’ve made is a fun scope that gets used a lot. The little travel case fits overhead or underseat on a plane. Plossls are fine for this scope and if you happen to have your scope lost or stolen, then the loss is basically the coast of a fine eye piece.
Here’s a sample of the Moon imaged very quickly using my old D70 (can see the mirror slap when you shoot) and not having cooled the scope (from the house @ 68 to 35 degrees) at prime.
I will never sell this little scope due to memories and the fact that for me it’s the perfect dual use scope. It’s tough and has good optics.
If you find one and its in good shape at the current used market price, well I think the little C90 is out of this world.