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Fingerprint on secondary mirror


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I've no doubt everyone will say leave it, but I just wouldn't be able to help myself, wouldn't be able to stop myself, I'd have to clean ANY mirror that looked like that lol, even if what's on it made no difference.

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I've no doubt everyone will say leave it, but I just wouldn't be able to help myself, wouldn't be able to stop myself, I'd have to clean ANY mirror that looked like that lol, even if what's on it made no difference.

I say leave it, but me being me................i could not live with it.

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Hehe, yeah well it is positioned on the edge of the mirror, but will probably feel like a thorn in my side regardless, despite possibly being fairly harmless. :p

Ive seen primary mirrors in worse condition and still being used. The fingerprint will not damage the secondary and it really wont hamper the views.

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I would certainly clean the finger print off.

There are amino acids on your (or who evers) hands and they will just love aluminium, and they will get through eventually.

Dust etc is one thing, the chemicals from hands etc is another.

If the finger print is not yours record it and go throttle whoever put it there.

Off topic but what are the Faroe Islands like for stargazing, imagine it is good.

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Clean it as you would a primary , mild soap solution luke warm water, agitate firstly without touching for very stubborn bits make sure your hands are degreased by leaving them in the same solition for 10 mins then very very gently disturb the offenders , finally remove and rinse with good quality distilled water and I dry with a cold hairdryer,some just stand and leave to dry naturally but its your choice. just treat the surface like its made of the most delicate thing you can think of and you won't go wrong.

ps cut your finger nails and remove the wedding ring, ........

Edited by LeeB
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I'd clean it. It won't affect the views, but it might over time lead to coating wear. I would do the following:

Remove the secondary and displace the dust from its surface using a squeezey-bulb air blower or squirting distilled water over it. That will reduce the risk later of scratches from dust on the surface. The fingerprint is oily so the water won't shift it. Pouring ethanol over the surface should get rid of it. If it doesn't you can try dragging an ethano-soaked cotted pad over the surface. Just use the weight of the pad: no force. Let the ethanol and distilled water air dry. There are no salts so you'll get zero water marks. On the other hand, if you try wicking water droplets away with the tip of a piece of tissue paper you will leave a water mark.

Coatings are tougher than they're generally given credit for. So it's fine to clean them, just don't drag dust and particles across the surface and don't drop the mirror (!) Take a look at how tough they are:

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Coatings are tougher than they're generally given credit for. So it's fine to clean them, just don't drag dust and particles across the surface and don't drop the mirror (!) Take a look at how tough they are:

Damn, gaffa tape, that was scary! :p

I'd prefer not have to remove my secondary mirror to clean it. Maybe I can put something below it to soak up, and then pour on it as it is positioned now.

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you don't need alcohol or anything special , a spot of washing up liquid in the warm water will degrease a fingerprint I've done it 10's of times. with no difficulty.

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Haha yeah, I've spent forever collimating that mirror, right now it"s really good. At some point I want to flock the tube as well, so I won't be able to avoid removing the mirrors forever. :)

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As above, Always remove to clean mirrors, don't be afraid of collimation it gets faster with practice, so look at it as a learning exercise. With practice you should be able to strip the optics out clean them(dry with cold hairdrier) and have them back in fully collimated in less that 45mins. I allow an hour for my 10"oo once a year. All the fear of collimating is lack of practice.

Edited by LeeB
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  • 1 month later...

Sorry for bumping this thread, but I finally took out the secondary mirror (super easy) and washed it with mild soap detergent & tap water, but I don't have any distilled water to rinse with afterwards, can I just rinse it with normal tap water and let it dry & then re-insert it, or is it really necessary to give it a rinse with distilled water? I imagine the secondary mirror gets dew'ed by water that isn't it completely clean in the outside environment anyway.

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