'H' CAMERA

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP68B00724R000200230012-2
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 3
• Document Creation Date: December 12, 2016
• Document Release Date: February 8, 2002
• Sequence Number: 12
• Publication Date: November 15, 1968
• Content Type: MF

Approved For Releas 62002/06/13 : 1 68B00724R0002X30012-2
IDEA-08 5-68
Copy of
MEMORANDUM FOR: Deputy. for Operations, OSA
SUBJECT "H" Camera
1. Recent missions with the "H" camera against coastal
targets of Southeast China have produced photography whose
scale and ground resolution were insufficient for target
identification. Although the camera performed well and the
missions were flown according to plan, the slant range
(35 to 45 nautical miles) and the presence of clouds and
haze degraded the imagry to an unacceptable degree.
2. While this problem is not a new one, it is one that
we have given a considerable amount of attention to in an
effort to improve the photographic results. The camera at
present is being operated at 1/500 second exposure using
3400 film and a wratten 12 filter. A wratten 21, orange or
wratten 25 filter could be used, but flight tests using
21 and 25 filters showed no improvement over the #12 filter
and there are two disadvantages to using #21 or #25 filters:
(1) the exposure time must be increased to compensate for
the greater density (light transmission value) of these filters,
thus causing a greater risk of image movement during exposure,
and (2) the lens must be refocussed for the longer wave length
of orange or red light. The lens is focussed within plus or
minus .001 inches, and the automatic focus control compensates
for variations in pressure and temperature in increments of
.00136 inches per pound per square inch and .0009 inches per
degree F. Thus, unnecessary refocussing of the lens in the
field are regarded as risks that should be avoided.
3.
Filter Factors of High Altitude Films
Films
Wratten Filter
12
21
25
3404
1.5
1.9
2.9
3400
1.9
2.4
4.0
3401
1.7
2.5
3.8
IDEALIST
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The filter factor is the number of times that you have to
increase the exposure to compensate for the loss of light
reaching the film. If .002 seconds gives the correct
exposure for 3400 film with a wratten 12 filter then the
exposure has to be more than doubled to use a wratten 25 filter.
4. Why use a filter?
A clean atmosphere is composed largely of
nitrogen and oxygen molecules that are much smaller than the
mean wavelength of visible light and would therefore have
little effect on photographic recording. The real atmosphere
contains larger particles of water, dust, smoke, pollen and
similar aerosols whose size approximates or exceeds a wave
length of light. Most of these particles are below 30,0001
altitude. As sunlight passes through the atmosphere and is
reflected back from the earth a complicated process of scattering
attenuation, reflectance and absorption occurs. We are really
concerned only with the image forming light that is reflected
from the ground target and makes its way back through the
atmosphere through a window off of two mirrors through a lens
system and on to the film. As the relative humidity increases,
more water particles are suspended in the air and more of
the light is scattered going downward through the atmosphere
and back as reflected light. The color of the scattered
light is a function of the size of the particles in the
atmosphere and is predominantly blue since the shorter wave-
lengths are scattered more than the longer (red) wavelengths.
In aerial photography a yellow wratten 12 filter is used to
reduce the effects of highly scattered blue light. When
comparing the contrast of a ground scene with the contrast of
the same scene viewed from 70,0004 it is noted that a ground
scene of 8 to 1 contrast (very high) drops to 5 to 1 with the
solar altitude at 90? (directly over head) and down to 1.5
to one with a solar altitude of 40? at 70,0004. This is under
ideal conditions with the target or ground scene directly
below the aircraft. At offset distances of 35 to 45 miles
the contrast of the scene at the camera is decreased by a
factor of?3 by the presence of 3 times as much scatter due
to the optical path being 3 times as long.
5. The lens in the "H" camera currently at Detachment H
has a focal length of 66" and an aperture of F/5.6 however
laboratory tests show that it produces better resolution when
stopped down to F/7 which further reduces the amount of
available light for recording imagry.
Approved For Release 2002/06/1 E ODP68BOO724R000200230012-2
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IDEA-0835-68
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6. Since the H camera is a complex piece of equipment
and is sensitive to pressure, temperature, and vehicle
movement and requires careful pilotage to cover targets at
large offsets, it is thought best not to introduce any new
techniques that would involve the risk of reducing the
current capability, particularly since there is only the
single camera at Detachment H with no back up. Best results
will be obtained at the highest solar altitude in the clearest
weather with the sun nearly behind or in front of the aircraft
permitting shadows to provide more contrast to the target
scene. Some possibility exists of using a higher resolution
film with smaller granularity such as 3404 or 60-243 however
the light sensitivity of these films is 9 times less than
3400 currently being used. It is felt that these films might
be used during the summer months (higher solar elevations)
with the U-2R (more stable vehicle) and probably will require
the use of one of the other two H cameras which can operate
at the full aperture F/5.6 thus providing more useable light.
These options will be explored at Detachment G to verify 25X1A
possible improvements.
S SD R&D OSA
SSD/R&D/OSA
V15 Nov 1968
Distribution .
Copy 1 - D/O/OSA
2 - DD/SA
3 - D/R&D/OSA
4 - D/M/OSA
5 - IDEA/O/OSA
6 - SSP'J/R&D/OSA
7 - SSD/R&D/OSA(Chrono)
8 - RB/OSA
Approved For Release 2002/06/13 : CIA-RDP68B00724R000200230012-2
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