322 THREE-DIMENSIONAL PHOTOGRAPHY
Separation.-Stereo parallax results from
the existence of two optical (visual) sta-
tions. The distance between these is the
separation. Normal ocular separation is
assumed to be 65mm, but in fact varies
widely through several millimeters upon
each side.
Slide.-Common name for the stereogram.
S. commercial.-Stereograms made for
sale to the general public rather than
for private use.
Sliding base.-A camera base, usually tri-
pod head, which enables a conventional
camera to be moved laterally 65mm so
that stereo negatives may be obtained by
successive exposure.
Space control.-A method of stereography
in which objects can be given an apparent
position in space which is not the natural
one. A miniature human figure for ex-
ample can be posed upon a tabletop with
every appearance of realism.
Spreader.-A stereogram with unit images
too far apart necessitating divergence of
the optic axes, painful at best and impos-
sible for most.
Stereo.-Abbreviation for stereoscopic, also
as prefix for many compound words.
S. book.-A book illustrated by stereo-
grams.
S. calisthenics.-Exercises for the eye
muscles obtained through viewing spe-
cial stereograms. Intended to nroduce
visual comfort and skill rather than to
relieve definite visual malfunctions.
S. chromatism.-The extrinsic depth
factor provided by the alteration of
chroma and saturation of color with
distance. Of vital importance in repro-
ducing stereo depth.
S. copier.-A special support for the
stereo camera in making copies of other
stereograms and in photography of
small objects.
S. diplopia.-The diplopia or double im-
age vision normal to all objects outside
the macular field, in stereoscopic vision.
S. drawing.-See Drawing.
Stereogram.-The “picture” used in ster-
eoscopy. Two images either separate,
side-by-side, superimposed or integrated.
Stereogrammetry.-A specialized form of
stereoscopy used for making stereograms
which are used as a basis for measure-
ment rather than for visual examina-
tion.
S. Guild.-An international association
of stereographers which circulates collec-
tions of 35mm stereograms among mem-
bers.
S. infinity.-That distance beyond which
stereo relief can no longer be distin-
guished. Highly variable. As little as 50
yards for some individuals and as much
as i1/2 miles for others. Normal average
670 meters or roughly three-eighths
mile.
S. macro bench.-See S. copier.
S. macrography .-The stereoscopic pho-
tography of small objects at magnifica-
tions of -5 to +lo magnification.
S. micrography.-The stereoscopic pho-
tography of small objects at magnifica-
tions in excess of ten diameters.
S. microscope.-A compound microscope,
usually of the Greenough type which
gives a stereoscopic field.
S. mount.-A physical support for the
stereo pair. Usually cardboard in the
case of paper prints. Of cardboard, plas-
tic, metal or glass or combinations of
these materials for the 35mm films.
S. prism.-(A). The free vision stereo-
prism is a stereo novelty in the form of
a cubical solid in which a stereo image
is seen. Improved by HCM through in-
troduction of distributed critical angle.
(B). A stereo reflector or element there-
of, using prisms instead of mirrors.
S. $rojector.-A projector used for pro-
jecting stereograms upon a screen in
such a manner that they may be viewed
in relief.
S. radiogram.-An X-ray stereogram.
S. relief.-The appearance of solidity,
roundness and space seen in the stereo-
gram.
S. Society.-An international (British)
organization of amateur stereographers
which circulates collections of stereo-
gram3 among members, primarily of the
gx6-inch paper type.
S. synthesis.-The subjective rocess by
which the stereo image is bui8 up from
the two dissimilar planar images trans-
mitted to the visual centers fr2m the
two eyes.
S. Tach (Trade name).-4 device to
produce stereograms with an ordinary
camera.
S. telephotography.-Telephoto stereo-
scopic photography. Applied loosely to
any stereogram made with long focus
lenses, but can be correctly applied only
to parastereograms.
S. telescope.-An instrument invented by
Helmholtz which provides a magnifica-
tion of relief rather than the magnifica-
tion of size common to the conventional
telescope. The Battery Commander’s
binocular (scissors type) combines the