Re: C-90 comparisonsPosted By Larry Beach |
Hi Billy, great to hear from you again.
The optics of the C90 have always been good.
The main advantages of the new C90 is the focuser, and
Modern coatings. The old system used a helical system that had the whole top part of the
C90 screw in and out for focus, Those can get very stiff in Cold weather.
Plus the grease in those are all drying out now.
If you want to replace the grease there is a hidden screw under the tripod mount that acts as a stop, and has to be removed. White lithium grease works well and stays fairly smooth. Doing this can also help with collimation from the tube sagging.
The old grease should be cleaned out with a petrol base cleaner, followed by an Orange oil
wipe.
The old coatings are close to 30 years old and are getting tired. A great number of the early C90's do not have Multi Coatings on the Meniscus.
There are rumors the newer optics are a bit better and collimation is better.
I hope this helps.
Larry Duane
The optics of the C90 have always been good.
The main advantages of the new C90 is the focuser, and
Modern coatings. The old system used a helical system that had the whole top part of the
C90 screw in and out for focus, Those can get very stiff in Cold weather.
Plus the grease in those are all drying out now.
If you want to replace the grease there is a hidden screw under the tripod mount that acts as a stop, and has to be removed. White lithium grease works well and stays fairly smooth. Doing this can also help with collimation from the tube sagging.
The old grease should be cleaned out with a petrol base cleaner, followed by an Orange oil
wipe.
The old coatings are close to 30 years old and are getting tired. A great number of the early C90's do not have Multi Coatings on the Meniscus.
There are rumors the newer optics are a bit better and collimation is better.
I hope this helps.
Larry Duane