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Thread: Cleaning objective lens

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    Default Cleaning objective lens



    Hi. I just realized that the inside of my Celestron 8" SCT has some dried grass pieces on it, but they are only in the periphery of the lens. Should I remove the lens and clean them with a soft brush? Or will the efect on imaging be small?

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    Default Re: Cleaning objective lens

    Be very cautious with the cleaning. I am sure some of the more knowledgeable members will give you sound advice. However, I am dying to know how grass got on the INSIDE of the corrector lens/plate! Lol! Bill
    Burris

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    Default Re: Cleaning objective lens

    Hi Claudio,
    The effect of a small piece of grass on the front corrector or primary mirror will be negligible. If it gets on the secondary it may show a small artefact.
    The corrector element can be removed but recollimating the front element can be tricky. In this case I don't think it is worth disassembling the front element.
    Joe
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    Default Re: Cleaning objective lens

    The corrector plate coatings are pretty tough. I got my C8 from my dad. It had spent years in in his workshop at his home in Tuscon.
    It was really dirty. I removed the corrector plate for cleaning. I covered the secondary mirror with saran held with a rubber band. Swept of the loose dirt with a camel hair brush and them sprayed Windex on the glass surface. Let it soak for a few minutes then wiped it off with cotton pads from the center out. Came out sparkling clean and no damage.

    To remove the corrector, remove the small cap screws around the perimeter of the corrector, then the plastic ring.
    There will be 4 cork pads that center the corrector. I marked the position with a sharpie. I also made an alignment on the edge of the corrector so it was reinstalled the exact same way it came our. I did find information that there will be a serial number etched into the edge of the corrector ad it will be the 3:00 position as viewed from the front. For reference the focuser knob is at the 9:00 position.

    I have heard cases where the corrector plate becomes stuck to the aluminum frame. A soak with alcohol and gentle prying with a non metallic object will free it up.
    If do a google search there are videos on how to completely disassemble one.

    If you really want to remove it.
    Do the disassembly on the floor with layers of towels under. WARNING! If you break the corrector plate, the telescope is basically junk.

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    Default Re: Cleaning objective lens

    Good advice above. Proceed carefully.
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    Default Re: Cleaning objective lens

    Unless its very dirty , like mine was due to 40 years of use leave well alone the corrector lens tend to get stuck and they are shimmed in place so need to be replaced in the same position using the same shims , if those get damaged then you have to make them
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    Default Re: Cleaning objective lens

    I'd leave it alone.

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    Default Re: Cleaning objective lens

    Quote Originally Posted by not_Fritz_Argelander View Post
    I'd leave it alone.
    Almost always the best thing!

    I clean my correctors and objectives when or if I see,

    • pollen (can adhere and scratch)
    • wind blown dust (gritty)
    • mold (can etch and cloud)


    The corrector like the objective lens of a refractor is not in focus. Dirt and even cracks and scratches are perceived if you can percieve them at all as reduced contrast.

    After I bought my firest scope I started looking on the web for advice about cleaning. Now I know that this is like advice on a mystery religion, with rituals and magic potions.

    The corrector coatings are bonded at the molecular level, they are not going to wash away or rub off easily. Windex or eyeglasses cleaner are good choices, and plain facial tissue, cotton balls, micro-fiber cloth and in a pinch a clean soft cotton t shirt or sleeve. If you have a soft brush or bulb blower you can use them too. Or you can get the formula for a magic cleaning solution (often water or alcohol and a tiny amount of detergent/suficant) or "quadruple-distilled, triple-filtered through charcoal and triple-filtered through Herkimer diamond crystals."

    Or if you must, you can follow these instructions from the Celestron support site.

    If and when you feel you must remove the corrector plate take a few minutes to find a set of directions with pictures for the make and of scope that you have. For example older Celestron scopes, made in the US have locator marks/serial numbers on the edge of the corrector which are used to orient the plate to the tube. The newer China made models do not. One tip is to use strips of tape from the face of the corrector onto the tube to create witness marks so that you can put the corrector back exactly as it was.

    If tragedy strikes and the corrector fragments the good news is that the cost of fixing is is actually lower than it was when Celstrons were made in the US. Instead of requireing you to buy an mirror and a corrector, they will now simply replace the corrector. Less expensive but not cheap. The other news is that a cracked corrector might still work. I'm told that David Levy was satisfied to use a C-14 with a cracked corrector plate.
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    Default Re: Cleaning objective lens

    There's another post about cleaning, there's good information.
    I'm about to clean my telescope too, lots of dust in Antofagasta!

    I can't post the link yet, but this is the thread tittle:
    " How Clean Does the Primary Mirror Need to Be - Really? "

    Good luck!

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    Default Re: Cleaning objective lens

    I get my SCT cleaned by local astronomy store every bunch of years if it starts looking grimy. Cost is only like 60$ and they do a good job. I would opt for this rather then tearing it apart yourself.
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