Fingerprints on AR lenses

[Falstaff]

We sometimes see fingerprints on the concave sides of AR lenses where the operators have flipped them over (They always coat the concave side first).

I am seeing such fingerprints at the moment. They are invisible, even under an arc lamp, unless I breathe on the lens.

I am assuming that breathing on them would make no difference if the fingerprints were under the coating, but I do not understand why I cannot clean them off with cloths, detergents and solvents etc.

Perhaps touching the lens immediately after a side has been coated causes damage and leaves a permanent mark? It has been suggested that lenses at the bottom of a calotte may become slightly overcoated with material when the other side is coated. Is this possible?

On the good side, as far as I am aware, there have been no complaints by customers, but I find the whole situation alarming, and would like the operators not to touch the faces of the lenses at all. This would not be easy to implement or police however.

Any suggestions, or am I worrying needlessly?

Falstaff.

[scriptfiller]

Don't breathe on them.

[Chris Ryser]

I am seeing such fingerprints at the moment. They are invisible, even under an arc lamp, unless I breathe on the lens.

Falstaff.

Could it be that the fingerprints are on the AR coating but below the hydrophobic ?

[IC-UC]

There should never ever be any fingerprints on lenses. This means that the operators are not handling the lenses correctly when flipping them.

[essegn]

Perhaps touching the lens immediately after a side has been coated causes damage and leaves a permanent mark? It has been suggested that lenses at the bottom of a calotte may become slightly overcoated with material when the other side is coated. Is this possible?
Falstaff.

I am not sure if i understand right, but you can check the AR coated lens by spectrofotometer and immediatelly find out if was overcoated.
If you (personally) are able to flip over the lens without fingerprints, show the operators the way how to do that.

Anyway i can't understand how you can leave fingerprintes during the flip over. 1mm from both side of lens is for putting it into the ring in callote and it is enough when you catch the lens at the edge (in position like holder in DIP coating).

It helps to use some thinny rod (or pen without ink) to easy manipulate with lenses during flip them over.
In the worst case, you will not see fingerprints, but the only small dot from rod, when you use the thinny rod or pen without ink.