Here are some instructions on how to build a microscope digitizer and how to create a polarizing (petrographic) microscope:

Digitizing a microscope for either a M$ Windows or Linux operating
system is quite straight forward. The devil is as always in the
detail.

Materials:
* Web Cam (almost all will do except "Encore Express [ENUCM-11]",
which I have will NOT work for Linux 2.6.21.5 and before)
* 5/8" or wider elastic strip about 9"-12" long. Can be cut from
latex exercise band.
* Short piece of PVC pipe to closely fit over the ocular.
(A 1-1/4" OD thin walled PVC is 1-3/32" ID which served well.)
* A PVC end cap for the above.
* Quick tie.
* Cyanoacrylate (CA) to join the pipe and end cap. This step should not be
necessary especially if planning to create a polarizing microscope.
* Rubber band(s) or O-rings (from automotive repair store) to aid
in stabilizing the camera mount.
* Short 1/8" diameter dowel.

Optional:
* Enough Polaroid plastic from which to cut out as circle for
the substage swing out filter holder and to fit inside the
PVC end cap.
Construction:
1) Cut out the end/center of the PVC end cap sufficiently to allow
a clean fit of the web cam's face within the cut out. Sand
smooth. The hole cut out should be smaller than the diameter of the
ocular.
2) Push the PVC pipe fully into the end cap. It is not necessary to
glue the end cap and pipe, especially if planning to build this
as a petrographic microscope. If the fit is too tight, cutting slits in
the end of the pipe can make the fit snug but not so tight.
3) Lay the elastic strip across the end cap and down the opposing
sides of the PVC pipe. Fold the ends of the plastic back on
itself and insert a plastic or wood dowel about 1/8" in diameter.
This will prevent the elastic from pulling out from beneath
the quick tie in the next step.
4) Loosely tighten the quick tie around the elastic just enough
that the elastic will not migrate.
5) Set the web cam into the end cap and snug down the elastic strip
on one or the other or both side(s) over the web cam. There
should be some tension over the web cam so it will stay in place.
6) Finish tightening the quick tie just beneath the end cap.
7) Adjust the web cam for the closest focus possible.
8) Slide the PVC assembly over the ocular.
9) Start the web cam software on which ever OS is in use.
10) Adjust the microscope focus on a target of choice while observing
the screen display.
11) Use the software's printing capability to verify all is working.

To Create a Petrographic Microscope:
a) Cut out a circle of polarizing plastic that will fit within the
substage filter holder (about 32 mm).
b) Cut out another circle of polarizing plastic that will just fit
into the PVC end cap prior to inserting the PVC pipe.
c) Verify the direction of polarizing and mark it on the edge of
each circle. This can be determined by observing a horizontal
surface (e.g. road) through the circle, if the plastic does not
come with the plane of polarization marked. When the light is
dimist through the polarizing plastic off the horizontal surface
the plane of polarization is vertical.
d) The top polarize is mounted with the polarizing plane N-S and the
lower polarizer is E-W.
e) The Lower polarizer should be mounted on a thin but sturdy plastic
ring which will fit into the substage holder. DO NOT attempt to
glue any polarizing plastic with cyanoacrylate. The fuming that
transpires while CA sets up will damage the polarizing plastic.

I will be adding some pictures of the polarizers shortly. A picture of the digitizer is
shown in one of the pictures attending the "Rotating Stage" post.