Re Re PHOTO_3D digest 1355

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

In reply to Neil Harringtons query about digest 1355 William Carter
mentioned the 1677 microscope in response to my request for further
information about his mention of SL3D being around in the 1600,s. I
realised I had heard mention of this microscope by the capucin priest
Cherubim d'Orleans in relation to the history of stereoscopy before and
that I had a book with some information and engraving of it which is
probably from one of Cherubims own books. Such as "La Diotrique Oculaire"
or the book mentioned by William Carter or Perhaps Zahn's "Oculus
Artificialis Teledioptricus Sive Telescopium".  Acording to the book I have
by Wredden The Microscope "La Diotrique Oculaire" and Zahns book reproduce
figures of the eyepieces which shows that  they had interpupilary
adjustment. Wredden says that it had two objectives as well as eyepieces
which he calls a "True Binocular". The reproduced engraving is not at the
right angle to confirm this but I think it would easier at that time to
make a microsope from two raked microscope tubes as some modern stereo
microsopes use or use mirrors even prisms to reduce the base than produce a
beamslitting prism arrangment.
  However even if it was of the beamsplitting binocular type some of them
at least are capable of giving a stereo image even though this is not the
intention. I have already mentioned on this list three methods I found in a
book using red/ green filters in the filter tray and eyepieces or crossed
polaroids to preserve true colour or "D" caps in the eyepieces .The authors
explanation was that this enabled the left and right images to be seperated
to their respective eyepieces. When I first  tried the anaglyph method it
did not seem to work with a Watson systen 70 binocular. More recently while
trying to calibrate one of these for measurements with a stage graticule I
noticed that there was a small but measureable difference of 1/2 a division
between the fields of view.
  So I tried the anaglyph method again this time with quite large specimens
of chalk dust on a slide uncovered . This time it worked although it was
actualy pseudoscopic until I changed the filters around ,but when I removed
them to check the effect it was still stereoscopic although the filters did
enhance the effect a bit . The effect of the filters was more pronounced by
the way they could reverse the relief. I think the point is that the stereo
effect of this type of microscope is not normaly noticed because the
specimens are so small depth of field is limited because of the high
magnification and specimens are flatened under a coverslip so they are
virtualy 2D anyway.
 I have since obtained an old book "The Microscope" by Conrad Beck where he
mentions that some people doubt that beamspliter binoculars can give a
stereo image but adds. "Those who have used such a microscope dont retain
any such doubt and the explanation is quite satisfactory". This explanation
is essentialy the same as the other book but requires a diagram so I cant
reproduce it here.
He does not mention the anaglph or polaroid method and he says that the "D"
cap method would not actualy work(I have not tried it) because it would be
impossible the get it in the right position . What he does suggest is
setting the interoculars slightly wider than normal so that the unwanted
rays are blocked off by the edje of the pupil . With what he calls "modern"
microscopes it is even easier as they have eyepieces raked outwards (sytem
70,s are like this) and just moving your head back and forth will block out
the iner or outer rays giving stereo normal or pseudoscopic images . I am
not shure if this design was a trend which continued as our Kyowas which
are newer than the Watsons have straight eypieces . They a give a good
stereo effect however and I am not convinced I have to set the eyepieces
further apart than normal with these or the Watsons.
My own feeling is that because the beamsplitter is a Swan cube consisting
of two right angle prisms together to  make the cube . The seperation is at
least partly dependant  on "Total Internal Reflection" the reflected rays
having to be beyond the "Critical Angle" which for air seperated cubes
would be about 43 degreees . This means that the beamsplitting is angle
dependant so that a small stereo seperation is also introduced .

                                                 P.J.Homer



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