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[OM] Re: Simple question about 'clear' screens

Subject: [OM] Re: Simple question about 'clear' screens
From: Mark Dapoz <md@xxxxxxxxxxxx>
Date: Wed, 4 May 2005 00:08:15 -0400 (EDT)
On Tue, 3 May 2005, Jay Drew wrote:
> 
> Doesn't the varimagnifier help in that instance, especially if you've
> focused the crosshairs on the 1-11 or 1-12 while at the 2.5 setting?

Yes.  To quote from the OM bible (Mannheim, p299) about this whole issue:

"Focus the eyepiece of the Varimagni finder unit until the hairline graticule
of the screen appears clear and sharp.  These crosshairs are actually pairs
of fine lines, 0.05mm apart, intruding into the centre circle from the two
sides, top and bottom.  When the Varimagni is correctly focused, you should
clearly see the two separate lines of each pair.  With the combined camera
and Varimagni finder magnification (5.5 x at the normal Varimagni setting)
the visual depth of field is small enough so that you see the image sharply
only if it is correctly focused in the plane of the graticule marks.  So
adjust the camera focus until this image appears at maximum sharpness.  The
lens must of course be at full aperture during focusing.

As a check move the eye slightly to and fro sideways behind the eyepiece:
at the sharp focus setting the image detail must not shift relative to the
graticule lines.  If it does, this slight image parallax means that the image
projected by the camera lens is not exactly in the correct graticule plane.
Adjust the camera focus (not the Varimagni eyepiece focus) accordingly.  By
switching the Varimagni to 2.5X magnification (11 x overall) you get a still
better check of the aerial image sharpness, though at the cost of not seeing
the whole picture area."

So there you have it...... mark



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