stereo optics problem

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From:"Keith Ryan" <> (by way of histonet)
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Hi All

I am trying to help a student who has been bought a 10-40x stereo
zoom microscope with some image recording/analysis equipment.  The
microscope is totally unbranded - nothing on the body or the eyepieces
(except for magnification).

The problem is an apparent mismatch of the lamp intensity in the
eyepieces. In the right ocular, the illumination is brighter
centrally, and it zooms up concentrically - that's fine.  In the left
ocular, the brighter central zone zooms up to go out of the field of
view, to the left.  A centred specimen zooms up concentrically in both
oculars.  Any suggestions?  Is it a phenomenon of the different height
of the bulb, which is directly below the stage, and the specimen?  The
problem is apparently alleviated by putting a piece of velin tissue
(thin paper) under the specimen.  But this introduces a patterned

Keith Ryan
Marine Biological Association
Plymouth UK

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