250 THREE-DIMENSIONAL PHOTOGRAPHY
acquire from other sources, the necessary data concerning these
techniques.
are obtained without the use of the compound microscope, al-
though the conventional micrographic camera is used. This, of
course, is really a variation of macro technique, This is a camera,
usually mounted upon a vertical bed, with the lens pointing
downward. Beneath the camera there should be some kind of
stage or raised platform to hold the subject. This stage should
have a surface plate of glass, plain and transparent. It should be
so arranged that black or white or gray underplates can be placed
beneath the stage. There should also be a swiveled mirror be-
neath the stage for providing strong transmitted illumination.
While these things may be purchased, some of the best outfits
have been either homemade, or have been based upon a com-
mercial unit to which homemade accessories have been attached.
A convenient film size is 31/4x41/4, although anything between
21/4x31/4 and 5x7 may be used.
A great deal of work has been done in this field during the past
several decades, but naturally most of it has been in black-and-
white. Because the emulsions and the processing is unusual, any
discussion of the work has heretofore necessitated a prolonged
treatment of these subjects. Fortunately, stereo is almost wholly
color work, and as color is just as essential and just as attractive
in this field as in normal stereo, we will not give any space to
processing or to a discussion of the various special emulsions used.
It will be necessary for you to establish your own exposure data.
This will depend upon the light source used as to color, intensity
and distance and upon the color film you use. Remember that
sheet color film usually has a slightly different color balance than
Kodachrome A. The easiest way is to find some panchromatic
emulsion which has a sensitivity two or three times greater than
color film. This is used to determine the exposure by test, and
from that data you get the color exposure. The first color ex-
posures should be made with '/2 and 2x the computed exposure
as well as the computed one itself. These three will give you an
accurate check upon your computation. If you change your light-
ing setup, you must change your exposure. Meters can be used,
but you must learn how to use the meter for such work, particu-LOW-POWER STEREoMICR0CRAPHY.-The lower ma@ifiCatiOnS