cleaning the mirrors

[IK13]

I understand the danger of wiping out the coating, but how durable/fragile this coating actually is?

Many people say not to touch it, but some clean it up (here Matt does it with no ill effects http://mattdentonphoto.com/cameras/electro_inside/index.html).

Yet I can't find a reference to someone, who actually went too far and ruined it by using a particular solvent/cleaner or by scratching it...

 

[Pherdinand]

the danger is to wipe it when it is dusty. Or when you wipe it with something dusty.
If you make sure you blow off the dust first, then put a clean new lens cleaning tissue on it, then drop a droplet or ethylic alcohol (or better, methylic alcohol) on the tissue and pull the tissue off with one continuous movement, you should do no harm.
If it persists to be dirty, you can fold a new tissue in two a few times to get a clean and somewhat stiff pece of tissue, drop some alcohol on it, let it sukc it up for a second, then wipe it gently on the mirror surface.
But only ONCE. And with one continuous movement.

This is how high transparency coated laser mirrors are professionally cleaned when necessary.

The alcohol should be as clean as possible. No denaturate one, and no whisky. These will leave residues on the surface.

Many other solvents might attack the coating, immediately or in a longer time.

 

[clintock]

Not many people are quick to post stories of themselves wrecking a mirror!
I've played with a first surface mirror from a polaroid disposable instant camera to see how much it could take. It's easy to scratch.. I've also managed to leave a mark on the mirror surface of TLR mirror that I had taken out and replaced already. The old one was really dirty, so I cleaned it some, but it was degraded already, tarnished, so I didn't really care about it..
The spray canned air I blew on it I had just shaken, so some liquid was in the tube.
The problem with that is that the liquid blasts out of the tube so fast that it packs a punch when it hits the surface, on top of that the sudden impact might make it evaporate on impact, doing even more damage. This can damage a negative too.
So if you're blowing droplets off the mirror, make damn sure that there's nothing but the 'air' coming out of the tube.. Blow a little while aimed away, and never shake the can while blowing with it.
Most references simply say never to use canned air, because it's too hard to explain how to do it right.. With a hammer and chisel, one can both sculpt and destroy.

I also whacked an already toasted beam splitter in a yashica using a Q tip swab- that film was really only about one molecule thick!

A biggie to watch out for when cleaning SLR mirrors is the focusing screen. Any alcohol of most any type on that thing will mark it forever.. So you either need to remove the screen, which comes right out on serious cameras, but is a risky task in itself, or make a 'dam' the right size out of card to protect the screen from the back of whatever swab you deem safe. Don't scratch anything putting the protection in there!
I use partial cotton balls straight from the bag, never touched by me, dragged on the mirror by just their own weight, saturated with ethyl alchohol, but not dripping.
Then i use canned air CAREFULLY to blow the thing dry, being mindful of where the drops are going, avoiding the chance of getting any on the screen.

It's a bit of a bitch to clean first surface mirrors, more info can be found in telescope sites, those poor things are often open to the air and get condensation on them, so must be cleaned often compared to a slr/tlr mirror.

Prevention is better than cleaning those things, but some ebay finds of slr bodies that have been sitting breech up on a shelf for the past ten years are gonna need some help.

 

[IK13]

I wouldn't think of using canned air to clean any optics, period. Don't know if there's a "professional" grade canned air, but the one you get from OfficeDepot etc. spits out droplets of something (it's not just water).

I do have some cleaning supplies I used for cleaning the sensor on my DSLR - bulb blower, Eclipse fluid (high grade methanol I think), lint free pads...

I recently acquired Yashica GSN and have hard time focusing.
So I'm thinking to give the vf/rf a good clean. Don't know how much it can improve (?) and if it's worth the risk, and it would be a shame to ruin it.

Since there are two basic dangers when cleaning the beam splitters:
1. The coating might be scratched/scraped while wiping.
2. The cleaning fluid used might lift the coating.

Is there a list of safe materials (wipes, fluids)? Does it differ from one model to another?

 

[clintock]

The microscope part of Zeiss has a pdf on their web site some place giving instructions for cleaning the coated optics in their microscopes. They suggest one should make swabs out of bamboo sticks and sterile pure surgical cotton.
I think they used acetone? There was a thread here about it recently.

I personally fear using windex like products because they contain ammonia, which may react with metal. Or I should say with my lack of knowlege, I fear may react with metal.. Both AR coatings and mirror coatings involve metal.

The only danger using organic solvents is if it gets on plastic or paint or the glue that holds together glued groups. Other than that (!) the solvents are safe for coatings.

 

[Pherdinand]

As i said earlier: In professional optics cleaning we use 1: methanol 2: methanol 3: methanol 4:in the worst case, ethanol.
No "windex" or other funky kitchen accessories!!
And simple plain (Kodak made, but should not matter) "lens cleaning tissues". Use ONCE and destroy way. Try also not to touch it all over with your finger coz you put your skin oil on it and then wipe it all over the optics.
No rubbing, especially no back-and-forth rubbing.
And you have to make sure that first of all you get rid of dust particles that could scratch the surface by the cleaning attempt.

 

[Pherdinand]

The organic solvents are not really safe for metals. Sorry to contradict you, clintock. Some of them efficiently dissolve metal (prs3000 dissolves a 50 nm thick layer of Co in three minutes), some of them attack metal oxides (that are used in AR coatings), some of them just leave ugly residue behind. ANd many of them are bad for your health (like all the aromatic ones, -e.g. chlorobenzene is an excellent solvent but it is highly carcinogene.)

By the way just to give you an idea about the delicacy of half-reflecting mirrors such as used in rf mechanisms: A thin layer of metal e.g. silver or gold, of only 15 nanometers (thousand times thinner than a generic dust particle) is already totally opaque. For a half-reflecting (i.e. half-transmitting) mirror a layer of around 6-8 nm has to be used.

 

[Mael]

Yes, alcohol is the best. Lens tissue or even soft toilet paper (it is not designed to scratch ! 😀 but it leaves a lot of fibers, you would have to blow them away)

But beware, sometimes older mirrors won't survive a simple alcohol cleaning...🙁

 

[clintock]

The organic solvents are not really safe for metals. Sorry to contradict you, clintock. Some of them efficiently dissolve metal (prs3000 dissolves a 50 nm thick layer of Co in three minutes), some of them attack metal oxides (that are used in AR coatings), some of them just leave ugly residue behind. ANd many of them are bad for your health (like all the aromatic ones, -e.g. chlorobenzene is an excellent solvent but it is highly carcinogene.)

Please by all means contridict away! I need to know this- My father-in-law is a retired chemist, I could ask him, but his explanations go all the way to the big bang and involve lots of hexagons drawn on a chalk board and usually consume the rest of the afternoon. So alcohol it is! That's what I always use anyway, since I don't have to use a gas mask with it.. well, not with ethanol i guess.

 

[IK13]

Cleaned the vf/rf including the mirrors on the Yashica GSN and Konica S2 with no ill effects.

I used Eclipse DSLR sensor cleaning fluid (I believe 99.9x% methanol).