Setup...If you have a spare few hundred dollars to a spare
few thousand dollars laying around you can purchase some very
fine polarizing microscopes. If, on the other hand, you are as
economically challenged as I am you can make your current microscope
into a limited polarizing microscope with the addition of a couple
of inexpensive polarizing filters.
1960s Nikon SK-e Microscope. Copyright Thomas L. Webster 2003
above, polarizing filter material may be purchased in flat sheets
and cut to fit where necessary. In my setup (to the right) I was
able to purchase 2 linear polarizing filters designed to be used
on photographic camera lenses. Both filters together cost around
$30.00 at my local camera store and are optically flat having
little effect on the image transmitted to the film. Polarizing
filters cut from sheets may not be totally optically flat but
are still useable for observation purposes at least.
consideration here is that the specimen must lie between two polarizing
filters and at least one of the filters must be accessible to
be rotated. In my setup one of the polarizing filters (#1) simply
rests atop the centering condenser and can be easily rotated.
The #1 polarizing filter is the one I rotate to produce the maximum
crossed-polarizing effects. The second polarizing filter (#2)
sits within the macro bellows where indicated in the illustration
to the right. The macro bellows comes apart easily at that location
to insert the filter. The second polarizing filter actually sits
above the projection ocular (hidden by the microscope adapter).
Since my interest is in photomicrography it was of particular
importance that this second polarizing filter be optically flat
so as to not degrade the image projected onto the film in the
the position of the second polarizing filter does not allow me
to preview the polarizing effects through the microscope's binocular
eyepieces. To determine the effects of the crossed-polarizing
filters I must preview the image through the right-angle finder
attached to the camera. I have learned, however, to recognize
areas of strong polarization when viewing the sample through the
binocular eyepieces. Areas of strong polarization will look strongly
3-dimensional compared to the appearance of the rest of the sample.
Also, areas of strong color will show weak colors when viewed
through the binocular eyepieces. I scan the sample for these strongly
3-dimensional and colored areas and then switch to the right-angle
finder on the camera to view the final image that will be projected
on the film.
when viewing or photographing your sample result from the near
total extinction of background light between the two polarizing
filters. It is therefore important where in the optical
path you place additional filters. For viewing purposes a blue
filter is generally used to cool down the light from the illuminator
so that the light looks more white. For photographic purposes
I insert an 80 A, B, or C filter so that the light striking the
film is the proper temperature (in °K) to record colors properly
on color film. The plastic material these filters are made of
can cause the light from the illuminator to become depolarized.
This results in gray backgrounds rather than black. Sometimes
this can be attractive (as seen in the photo to the right) but
at other times this can be very distracting and disappointing.
It is important, then, to place any additional color correction
filters before the first polarizing filter. In my setup I place
the color correction filters below the centering condenser. Thus,
light passing through the centering condenser is already color
corrected before the light passes through the first polarizing
filter. (Continue to