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Re: [OM] OM-4 diopter adjustment

Subject: Re: [OM] OM-4 diopter adjustment
From: Chuck Norcutt <norcutt@xxxxxxx>
Date: Tue, 08 Jun 1999 20:56:54 -0400
Maybe this will help clarify the diopter adjustment question... then
again maybe it'll just muddle it up. :)

The camera lens is acting as a projector.  It's projecting an image onto
the _bottom_ side of the focusing screen.  The camera eyepiece is like a
loupe. It needs to be focused also on the _bottom_ side of the focusing
screen.  Its purpose is to view the image being formed on the _bottom_
side of the screen.

To cut out the _distraction_ of actually having an image there you first
remove the lens or else defocus it and point it at a bright, blank
area.  You then focus the camera's eyepiece on the _bottom_ of the
focusing screen using the diopter adjustment (or fixed diopter lenses if
you don't have an OM-3 or 4).

But it's hard to focus on the ground surface itself.  The easiest thing
to focus on is the rings around the focusing aids in the center of the
screen.  Since the rings form a continuous line they are easy to see. 
They are also on the _bottom_ side of the screen along with the ground
surface.

Once the _bottom_ of the screen is sharply in focus then any image
formed by the lens will also be in sharp focus... provided, of course,
that you haven't dropped the thing on the concrete and knocked
everything else out of whack.

Chuck Norcutt
Woburn, Massachusetts

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