For some strange reasons, I have been receiving quite a few PMs from newbies if they should clean their telescope lenses when there are dust, dried dewspots, etc, etc.
My answer is NO! Plain and simple.
Just remember this : It takes a lot, a lot of dirt to affect the images in the eyepiece. Very time you clean, you risk scatching the surfaces or even degrading the coatings on it. I have been there before. It is not worth cleaning over some dirt or dried dewspots. It affect nothing at all. Live with it and enjoy your scope.
So when should you clean? Ok..assuming you have a SCT. Stand in the front of the corrector lens. Can you see the full primary mirror? If yes, go enjoy your scope and stop worrying about "pristine optics at every angle". If you cannot see your primary mirror fully, then most probably you need a cleaning.
I remember there was once my former LX-90 got its front lens fully dewed up. I could hardly even see the primary mirror from the front. Even then I could still see M17 inside the eyepiece, even though the contrast is not as great as before. That tells you that it takes a lot a lot of "blockage (or dirt)" before it even affect viewing. I mean if an object like M17 can still be seen when the front lens got fully dewed up, those little dirt or spots on your lens is really nothing.
So stop doing the flashlight test and all that. It is really no point except frightening yourself.
100% clean optics are not neccessary!
I agree with Vincent that one should not be unduly concerned about cleaning off bits of dust particles on the mirror or lens. I have seen very dirty SCT corrector plates that still give very good views. It really takes lots and lots of dirt & dust to really visually degrade the image.
However, if there are signs of fungus (those tiny hair-like patches) or mildew on the lens or mirror, then I think it is best to clean it off early. Some of the mirrors and lens I have cleaned for my friends have these fungus and mildew on it, and if it is left too long, it may affect the coating on the mirror or lens, not so much as to degrade the image, but more of a 'cosmetic' uneven coating seen after cleaning.
However, if there are signs of fungus (those tiny hair-like patches) or mildew on the lens or mirror, then I think it is best to clean it off early. Some of the mirrors and lens I have cleaned for my friends have these fungus and mildew on it, and if it is left too long, it may affect the coating on the mirror or lens, not so much as to degrade the image, but more of a 'cosmetic' uneven coating seen after cleaning.
Yes, if there are fungus...you will need to do something about it. Thanks for rlow to add to my points.rlow wrote:I agree with Vincent that one should not be unduly concerned about cleaning off bits of dust particles on the mirror or lens. I have seen very dirty SCT corrector plates that still give very good views. It really takes lots and lots of dirt & dust to really visually degrade the image.
However, if there are signs of fungus (those tiny hair-like patches) or mildew on the lens or mirror, then I think it is best to clean it off early. Some of the mirrors and lens I have cleaned for my friends have these fungus and mildew on it, and if it is left too long, it may affect the coating on the mirror or lens, not so much as to degrade the image, but more of a 'cosmetic' uneven coating seen after cleaning.