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Re: [OM] Black specks on Focusing screen

Subject: Re: [OM] Black specks on Focusing screen
From: "Giles" <cnocbui@xxxxxxxxxxxxx>
Date: Wed, 20 Jan 1999 21:45:04 +0000
I suspect the screens are not machined at all.  They are probably stamped or 
moulded 
from a glass or metal master much in the same way as CDs are made.  That must 
be why 
they are plastic and not something harder and more durable.

I think any form of cleaning should be by a means which does not involve 
anything 
rubbing over the surface.  Lars' suggestion of ultrasonic cleaning is 
excellent.  
Take your screen to your local jeweller with some distilled water to clean it 
in.

I have another suggestion.  There is a non abrasive lens cleaning product 
called 
Opticlean.  It goes onto an optical surface as a liquid.  It then semi 
solidifies to 
form a skin which traps all contaminants including fingerprints, grease and 
dust.  
The skin is then peeled off leaving a clean surface.

I haven't yet used this stuff myself but will get some soon.  I think it would 
also 
be a safe method for cleaning front silvered reflex mirrors also.  It is 
available 
from Jessops in the UK and is thought by some to be quite expensive but if it 
will 
allow one to clean lenses, filters, mirrors and screens safely it might be 
worth it 
when one considers the potential cost of damage to any of these.

Giles

Garth Wood wrote:

> I've wondered the same thing.  The only thing I can think of is that the 
> screens are made out of a
> relatively soft plastic which allows for extremely fine-toleranced machining. 
>  If it's as soft as I
> surmise, then even a light cleaning with the wrong tools or methods would 
> scratch it irreparably. 
> 

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