Re micro 3D

[P3D Peter Homer <P.J.Homer@xxxxxxxxxxxxxxxxx>]

To reply to William Carter's posting "micro 3D"  I have used polarisers in
the filter tray of a microscope and eyepieces to get stereo using both
crossed 45 degree and vertical horizontal polarisers . One method did work
better than the other but until I check I cant be sure which it was , I do
remember it was the opposite to what I expected at the time . Because I did
this at work I probably tried " standard " scientific polarisers at first
IE vertical/horizontal and it worked but the polarisers in the eyepieces
were focussed and magnified by the second lens so that all the little
scratches on them were visible. So I tried wearing a pair of stereoscopic
polarising glasses and projection filters in the filter tray with 45
degrees polarisation. There did seem to be some "depolarisation" with one
of the methods compared to the other. I thought that this might be because
a couple of the prisms in the system were "Fresnel" rhombs which can
produce circular polarisation and at the time I thought this required the
light entering the rhomb to be at 45 degrees . But the rhombs themselves
are at 45 degrees to take the split beam to the two eyes so the 45 degree
polars would not actualy be at this angle while the vertical/horizontal
would. In fact Fresnel rhombs  seem to require unpolarised light or at
least two components at right angles to each other to produce circular
polarisation so I am not shure of the reason for the deplanepolarisation.
   The fact that with vertical/horizonal polarisation the light could be
entirely reflected or transmited at the prisms so that the right might see
the left not. Would not matter because the reverse would aply for the other
polarisation which is exactly what we want. This might be part of the
reason why it works but in fact this effect cant be very strong or you
would not need the second set of polarisers in the eyepieces and I am shure
I tried this and it did not work.
 I agree that any birefringent specimens that you might normaly observe
with a polarised light microscope would cause retinal rivalry problems with
a Polarised light stereo microscope.
The information about Schulman intoducing this sort of system in the 20,s
if he employed polaroid it would perhaps be one of its first applications
.Also the anaglyph version by edge scientific is this the edge stereo
microscope discussed in this group last year.              P.J.Homer



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