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REPORT OF COMMISSION VII
off, 1951); (4) radioautographic equipment by means of which invisible radiations
can be made manifest on photographic plates (Gorbman, 1948); and (5) ultra-
high speed motion picture equipment by means of which extremely rapid motion
can be stopped through the taking of photographs at rates in excess of twenty
million frames per second. For further information relative to each of the above,
the interested reader is referred to ‘Progress in Photography" (Spencer et al,
1950) and to Chapter 12 of the forthcoming, revised ‘MANUAL OF PHOTO-
GRAMMETRY.”
F. SPECIAL PHOTOGRAPHIC TECHNIQUES:
The following brief list is not intended as a complete exposition of various
techniques that might be employed to provide the interpreter with a better photo-
graphic image. However, it is indicative of the fact that we have by no means
exhausted all possibilities in this regard and that some of our fixed concepts are
worthy of reexamination.
(1) In the Pacific Northwest it has been found that photography flown
beneath a high overcast is superior to that flown on a bright sunny day, both for
multiplex mapping and for many types of photographic interpretation. The prin-
cipal advantage of such photography seems to be that it provides much better
detail in shaded areas. Shadows are especially pronounced in the Pacific North-
west because of the steepness of the terrain, the great height and density of the
vegetation, and the relatively high latitude. Although a longer exposure ob-
viously is required in order to obtain such photography, image blur caused by
this requirement was found to be negligible for photography flown at a scale
of 1/20,000.
(2) It has long been known that the combination of overexposure and under-
development of photographic film provides less contrast than normal exposure
and development. This technique is of such importance in permitting better dis-
cernment of photographic detail in shaded areas, that it has been specified as the
technique to be used on several recent photographic missions flown for various
civil purposes.
(3) When photography is flown at very low altitudes, and/or at times when
there is a minimum of atmospheric haze, a better aerial photographic image may
be obtained if no filter whatever is used at the time of photography. This, again,
is largely a matter of obtaining better detail in shaded areas, which obviously are
illuminated primarily by the blue light of the sky. Such areas show very little de-
tail when photographed through conventional filters, virtually all of which cut
out the blue end of the spectrum in order to provide better haze penetration.
(4) Some parts of the Earth’s surface are characterized by a patchy appear-
ance in which relatively large areas of snow, sand or other high light-reflectance
material alternate with large areas of dense timber, water or very low-reflectance
material. For example, much of the northern hemisphere between latitudes of
45° and 65° contains large patches of dense spruce or other dark-toned coniferous
forest, alternating with large snow-fields or bare granitic rock areas which appear
very light in tone on photographs. Experiments conducted in British Columbia
have indicated that, when taking aerial photography of such areas, it is both
feasible and highly desirable to give less exposure to those frames covering areas
which are predominantly light in tone, and more exposure to those frames
covering areas which are predominantly dark in tone. By thus giving each area
encountered on the photographic run a more nearly optimum exposure, photo-
graphic detail is generally improved throughout the run.
(5) The optimum focal setting for a camera lens va
photographic image. This is shown in an article by
ries with the size of the
Macdonald (1951) who
