CLOSE-UP STEREOGRAPHY 25 1larly how to compute the increase due to the extremely small
effective aperture used.
However, despite these minor difficulties, color is infinitely
preferable to black-and-white.
that the term “high-power” is relative only, and actually refers to
those stereomicrographs made with the aid of a compound micro-
scope. Actual high-power stereomicrography (200 diameters and
more), is disappointing because the depth of focus of the ob-
jectives used is so slight, and because most specimens have so
little thickness. It is not at all unusual for the microscope speci-
men to be cut to a thickness of two or three microns, and for many
types of tissue five microns is the maximum. As this equals
roughly 1/5 of i/iooo of an inch, it can be understood that there
is very little depth to be revealed.
Stereomicrographs can be made of these subjects, but such work
requires great care, and at best the relief is so slight that results are
disappointing. Therefore, even in the “high-power’’ field, the
magnifications of 100 to 200 diameters are customarily regarded
as the useful maxima, although these powers are ordinarily re-
ferred to as “low-power’’ in ordinary microscopic terminology.
As we have said, we have no space in this volume to discuss the
technique of microscopy, and if the interested reader has no
knowledge of the subject, it is suggested that he obtain a reliable
reference book (“The Microscope” by Belling is one of the most
practical), and acquire a working knowledge of microscopic tech-
nique before undertaking photomicrography.
The technique of conventional photomicrography is followed
throughout, with the exception of those steps introduced to pro-
duce the desired stereo relief. Assuming the reader can produce a
good planar photomicrograph, we shall consider the methods used
in obtaining the stereo relief.
Stereomicrography is closely related to ordinary photomi-
crography, just as normal stereo is closely related to normal pho-
tography. The same equipment is used and the fundamental
methods are the same. Parallax may be obtained either by lateral
displacement of the object, by object rotation or by control of
illumination. The last method renders a peculiar appearance
which could be called pseudostereoscopic if that term were notHIGH-POWER STEREOMICROGRAPHY.-It must be borne in mind