Finger print on primary mirror! Help!

[AlphaRob]

Just removed the primary mirror from my 250PX to make some mods, and caught the edge of it with my thumb, so now have left a small print on the outside edge. Should I clean it off or leave it? I know it wont affect the view much at all, I'm just worried about the finger grease corroding the coatings. If I clean it, how, and should I just do the whole mirror?

Any advice (other than to wear gloves next time )would be great!

[Stephen]

I'd be tempted to leave it. I'm not a fan of cleaning mirrors unless absolutely unavoidably needed

[acey]

I agree - leave until you're cleaning the whole mirror. The mirror has a silica overcoating and grease won't harm it. For now, when putting the mirror back in its cell, position the fingerprint under one of the clips. Those clips do more to affect the view than a fingerprint will.

[Quatermass]

leave it untill your mirror needs a good clean. I have cleaned my mirror 5 times in the last year its not hard to do. I just clean it with a soft cloth after a wipe with a damp one a photographic cloth with no furry bits mind.

Sent from my GT-S5670 using Tapatalk

[kenmyers]

Cleaning Optics

This is a very helpfull guide on cleaning mirrors and lenses but be warned, if you ruin it, a cloudy sky wont be the only thing stopping your views.

I would say DONT CLEAN IT. My friend has two rather large fingerprints on his dob 5" primary (it happened as he was building it) you can see them very clearly if you look into the tube opening - but with an eyepiece we get super views and can not see any marks at all.

[PreludeToADream]

Like others have said, I would advise not cleaning it. My view is not to clean your mirrors unless ABSOLUTELY NECESSARY.

[AlphaRob]

Cheers guys, thought that would probably be general idea, I'm just glad the grease wont corrode the mirror coatings. I've seen the damage finger prints can do to some polished surfaces!!

[Yimini]

While attempting to collimate my reflector for the first time, I managed to get a smudge on the secondary mirror I just wiped it off with a clean cloth. Have I made a novice mistake here, or need I not worry?

[tom714uk]

You may have made some very dine scratches but I wouldn't worry. I left my dob out a few weeks ago and it got completely frosted up, then without thinking I left it upright to defrost inside. Result was dirty marks on both mirrors. I read up on cleaning in a panic and the general message was you usually don't need to! The views through my scope I'm happy to say have been absolutely unaffected.

I read somewhere that it's been mathematically proven that for a mirror of 8" or so you'd need a solid black mark an inch or two across to make even the slightest visible difference. When we look through a scope we're focusing a long way past the mirrors I guess so all that matters is the total reflecting area present, which is hardly touched by most marks. (I'm open to correction if I'm wrong on this.)

Tom

Sent from my HTC Desire S using Tapatalk

[Peter Drew]

Spot on Tom.

[perrin6]

I'd leave it unless you have 10-inch wide thumbs !