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[OM] Cleaning oily films off of glass

Subject: [OM] Cleaning oily films off of glass
From: Joe Gwinn <joegwinn@xxxxxxxxxxxx>
Date: Tue, 29 Jan 2002 13:08:51 -0500
Brian,

At 5:18 PM +0000 1/29/02, olympus-digest wrote:
>Date: Wed, 30 Jan 2002 00:11:57 +1300
>From: "Brian Swale" <bj@xxxxxxxxxxxxxxx>
>Subject: [OM] Cleaning lenses
>
>Hello folks,
>
>Can I ask for a bit of advice? (of course)
>
>I just got a lens back from having fungus removed - as much as he could get 
>at. The lens is a Mamiya Press 100mm, and the front element is screwed on 
>very tight.
>
>The rear lens element lives in a huge cavern surrounded by helicoid threads 
>etc.. I noticed that the outside surface is covered in a kind of oily film 
>that 
>you don't see by looking at the lens surface with reflected light, but if the 
>lens is opened up and a light shines through, it is very obvious.
>
>I tried removing this by huffing on the element and wiping with Oly lens 
>paper, but that really didn't work. The muck just spread around a bit more.  
>It 
>needs an organic solvent. It's go to go - it surely acts like a soft-filter 
>and I 
>don't want that. The 100 has a reputation of being a sharp lens and that's 
>why I bought it - to yield sharp images.
>
>I wonder if the iso-propanol that is used for cleaning tape recorder and video 
>heads would do the job without damaging the lens. I think it should - but am I 
>correct?

I would first use denatured alcohol, as was suggested by another poster.  One 
can buy 99% Isopropyl Alcohol at drug stores, but denatured alcohol is more 
aggressive, and can be obtained at hardware and paint stores by the gallon.  
Neither will remove paint, such as the anti-reflection black paint used inside 
lenses.

By the way, I've had good luck using alcohol to remove fungus.

If alcohol fails, I would use Acetone or Methyl Ethyl Ketone, which are also 
available at hardware stores and paint stores by the gallon.  These are more 
aggressive than alcohol, but will affect paint, so use a damp (not wet) 
wooden-handled Q-tip and be careful.  If the oil film is significant, it's 
probably a good trade to live with some loss of paint around the lens.

The next step up is Toluol, available in some pait stores.

If the film resists Acetone and MEK and toluol, which can happen if the oil 
film has cured like paint, paint stripper is needed.  I would very carefully 
use a Methylene-Chloride based stripper such as 5F5, applied and removed with a 
Q-Tip.  Use the prior solvents to remove the traces of 5F5.  

An alternative approach is to use pure Methylene Chloride, which can be 
obtained by the gallon from plastics supply houses (used to solvent-weld 
plexiglas), and by the expensive half-ounce from model shops (used to thin 
Testor's paint).

I would *not* use a lye-based paint stripper.  Lye will etch aluminium, and may 
strip the anti-reflection coatings as well.  And, it's hard to get all the 
residue off, and that residue will likely cause corrosion.  How to tell?  Read 
the health warnings.  It should complain only of Methylene Chloride (and Methyl 
Alcohol) and should not warn of Sodium or Potassium Hydroxide, or anything 
else..

These solvents will not affect lens coatings, but be very gentle with the 
Q-Tips.


Joe Gwinn


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