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Re: [OM] OM1 Viewfinder Black Cloud

Subject: Re: [OM] OM1 Viewfinder Black Cloud
From: Mark Dapoz <md@xxxxxxxxxxxx>
Date: Thu, 19 Jul 2001 10:31:24 -0400 (EDT)
On Thu, 19 Jul 2001, O.C wrote:

> The problem described that occurs with the foam and prism is that the foam 
> rots and becomes bound to the prism surface. When stuck on the glass it 
> alters the glass to air interface that is required for the total internal 
> reflection to occur. What you see instead is the foam through the glass. 
> Thats why cleaning the prism of the gunk and restoring the original glass 
> air interface will restore things.

In theory what you describe is true, but I've found in practice that's not
the case.  I have a prism which is about 80 0e-silvered.  I can get it
to work reasonably well if the prism surface is perfectly clean.  Unfortunatly
problems arrise at the sharp edges of the prism (at the top and around the
eyepiece).  At these points you can clearly see a faint line in the viewfinder.
No amount of cleaning will make these lines disappear.  I suspect the silver
backing which is applied to the prism somehow "fixes" this problem.  A prism
with no silver backing is still useable, it's just not as good as one with a
silver backing.
                                        -mark


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