APPENDIX B
and which is in full, corrected, natural
color. By all means the most perfect type
of photograph yet produced.
Parallactic distm-tion.-A degree of paral-
lax too small or too great for the object
size. Objects appear as thin (i.e., silhou-
ettes) or elongated in the direction of the
optic axes.
Parallax.-A difference. Specifically the dif-
ference of the visual images which result
from the two eyes having different points
of view. The fundamental external stim-
ulus of stereoscopic vision.
Absolute P.-The parallax of a given
point as determined by the angle be-
tween the visual axes meeting at that
point.
Circular P.-Stereo relief produced by
rotating the object rather than by hav-
ing two separate points of view.
Diflerential P.-The variation between
the parallax of two points upon the
surface of an object. The fundamental
external stimulus which enables us to
see roundness or spatial difference.
Dynamic P.-The eier changing paral-
lax involved when the eyes shift from
object to object. The specific external
stimulus of stereoscopic vision.
Illumination P.-In stereomicrography
the production of parallax by opposed
light beams rather than by physical dif-
ference.
Relative P.-Th- parallax of one object
or point as compared with that of an-
other. Closely similar to differential
parallax but used as a basis of meas-
urement.
Rotary P.-See Circular parallax.
Stereo P.-Parallax as specifically related
to stereo vision and in contrast to strictly
geometric parallax.
Parallax stereogram.-Commonly but in-
correctly used to designate an integrated
stereogram. Because parallax is the vital
factor in stereoscopy, any stereogram of
any type might properly be called a
“parallax” stereogram. A free vision ster-
eogram, see Grid stereo.
Parallel vision.-The normal condition of
vicion at complete rest. In stereo the abil-
ity to fuse a stereogram of conventional
type without the use of a viewer. Accom-
plished by separating the habitual co-
action of convergence and accommodation.
Parastereo.-A stereogram which is appar-
ently ortho in quality but which can be
demonstrated to possess the anomalous
spatial relationship of the stereo telescopic
field. To all intents and purposes an or-
thostereogram of telephotographic type.
PePax.-Coined term to indicate the rela-
tionship between the apparent size and
the apparent relief of any object. Normal
PePax is characteristic of the orthostereo-
gram. Abnormal PePax indicates paral-
lactic distortion.
Personal.-A miniature stereo camera
using standard 35mm film but making 70
stereo pairs of substantially 16mm size
upon a standard 36 exposure film. Also
applied to camera and mounting acces-
sories made bv Sawyer’s, Inc.
Perspective.-The disposition of lines to
represent a solid object upon a plane sur-
face. In stereo regarded as the complement
of parallax. Perspective has to do with
“size-in-width” while parallax has to do
with “size-in-depth.”
Planar.-Restricted to a single plane. Or-
dinary photography in contrast to stereog-
raphy,
Polarized light.-Light which vibrates sub-
stantially in a single plane. Used in stereo
largely because of its property oE extin-
guishing an image when planes of polar-
ization are crossed.
Polaroid (Trade name).-A synthetic mate-
rial which has the property of polarizing
light. Used in stereo projection of polar
anaglyphs.
Prismatic stereoscope.-A stereoscope in
which the Ienses are really half lenses, thus
forming spherical prisms. The Brewster
type of stereoscope. Also a reflecting ster-
eoscope using prisms. Often an autotrans-
posing viewer.
Prism diopter.-The unit used in meas-
uring the amount by which a beam of
light is deviated by passing through a
prism. One prism diopter deviates one
unit in 100.
Projection gage.-A film gauge to facili-
tate mounting stereo films with the cor-
rect separation to compensate for various
ranges of deviation.
Pseudoscopk-The effect of untransposed
stereo images. Depth values are reversed
with far objects seen nearby and vice
versa.
Pseudostereorcopic.-A “stereogram” made
up of two identical images. As there is no
parallax, no stereo relief is seen. Such
pseudostereograms have actually been
marketed as stereograms.
Realist (Trade name).-A widely popular
35mm stereo camera. Also generic name
for a projector, viewer and other 35mm
stereo acceqsories made by David White
Company.