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  1. #1
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    Default Very Old C-8 - cleaning



    Hello, new to the forums and first post. I have an old C8 I bought in 1976. If I've used it 100 times over the past 35 years, I'd be surprised. It's in excellent condition on the outside, always kept in the case.

    I recently moved to a house that is elevated 200' above most of the local terrain and I can see about 20 miles down the coast. This view has sparked me back to wanting to use the scope for terrestrial viewing and maybe some terrestrial photography - although I am a complete novice in photography.

    I've taken the scope out of the case and noticed that on the corrector lens, there is quite a bit of haze on both the inside and outside. I've looked thru the scope on a bright day and the image also appears more hazy than I remember from past viewings (terrestrial). I am very mechanically inclined and would like to clean not only the corrector, but if needed, the primary and secondary mirrors - but only if needed. If there is only the haze, and no particulates on the mirrors, is it worth cleaning them versus possibly scratching them? I've read that a 50 to 70% alcohol is best for this purpose. Are cotton balls best to use or could I use a brand new microfiber cloth?

    I would assume that the corrector lens needs to be put back into the same exact position that it is in now?

    Besides checking collimation, Are there any other mechanical maintenance items that I should consider doing? Thank you for any suggestions you have!

  2. #2
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    Welcome to the forum BVHC8. Can't give any advice from personal experience, but I can say that being mechanically inclined is an asset. These are not particularly complicated mechanisms.

    My one and only venture into cleaning was pretty scary, though. My G-8N had sat in the corner of the living room of a smoking family for 10 years before I bought it. The alcohol wouldn't touch the film. I finally ended up using Fantastic, but I don't recommend it, because it says on the bottle not to use it on glass.

    Of course, I didn't discover that until after I had finished. Luckily, the glass was protected by the coatings.
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  3. #3
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    It is something that you can do. There are some useful websites and forum posts on removing and replacing the corrector plate and cleaning.

    Cleaning methods and supplies--
    Arkansas Sky Observatory - 2001. The golden rule not to begin by wiping a dirty corrector plate but use low pressure air or very soft brush. Work with a light touch clean the plate in sections. Don't wipe/blot a clean section with a tissue or pad used on another section. It's all covered in the instructions.

    There are other sites and other cleaning solutions that I'm sure work just as well.

    Removing the plate. Start here for links to some good sitesHow do I remove the optics from the optical tube assembly (OTA) of my Schmidt-Cassegrain telescope (SCT)?

    If you are lucky you won't need to clean the mirrors. Some small spots or hazy areas won't have much impact. But you can clean them.

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  5. #4
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    Just finished cleaning. Removed the lock ring and found the serial # and black "tick" mark on the corrector and it was nearly at the 3 o'clock position. The glass was just a bit tough to remove, Steady pulling pressure with 4 fingers on the secondary mirror housing finally broke the seal. No tools used. Three cork shims stayed in place. The insides were remarkably clean. Two visible "large pieces of lint and a mild amount of very small lint. I test cleaned a dime sized portion of the mirror and decided it did not provide much of a difference so I didn't clean it nor the secondary mirror. The coating (alum, silver or?) was in very good condition. Put it back together and really can't say I see a difference even though the haze on both sides of the corrector was plainly visible. But I'm happy knowing I'm getting as little light loss as possible.

    The one obvious thing I noticed is a grease/oil film on the entire bottom surface of the tube extending (wide) from the back and out to the front where it narrowed. I'm going to assume that this is from years of the tube facing down and probably some grease vapors from the focusing mechanism getting warm and migrating down the tube? It's a very light coating, nothing that concerns me.

    I owned a WWII anti-Aircraft searchlight (commonly known as a Hollywood grand opening light) Its' 60" mirror was made of brass and was plated with Rhodium. I could easily see the rough surface of the brass casting starting to show through the thin Rhodium. This is my frame of reference with mirror plating so by this standard, my C8 mirrors are pristine. (Can you imagine the price of re-plating the 60" mirror - if you could find a plate'r with a tank large enough) Thank you for ally your help!

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    The corrector plate and your eyepiece glass is NOT as fragile as you think. They are NOT a mirror, and the coatings are quit durable. Just be careful that you do not have sand grit that you push around the surface. So blowing off the surface and also brushing it gently with a soft brush before cleaning is needed.

    Don't say I told you but filtered plain blue Windex will work just fine. Al Nagler uses this on his EYEPIECES! However I would use the formula listed above by Dr. Clay to clean the corrector plate.

    IT MUST BE replaced in the exact position it was in before you took it off, and there may be tiny cork shims under the glass on the edges that must also be replaced exactly.

    EVEN A 7 Year old can do this, this is "child's play" -- see this web site: Ha!

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