GV—58 PHOTOGRAMMETRIC ENGINEERING 
OPTICAL COMPONENTS 
The various models of flight analyzers are equipped with lenses particularly 
adapted to their requirements. The Model IV uses a coated element, 93 degree 
field, wide-angle Bausch & Lomb 6 inch f:6.3. Metrogon lens. The Model VI 
analyzer uses a coated element 12 inch f:5 Eastman Kodak lens. The Model 
VII-B analyzer uses a 24 inch Bausch & Lomb Aero Tessar. 
Since the targets being photographed are generally at a great distance, the 
amount of light reflected from the object is of a very low order. Also because of 
the distances involved, and because the background is usually extremely bright 
and tends to diminish the apparent density of the target, the contrast ratio is 
very low. These factors, plus the fact that the target background may be the 
earth at one phase of its flight and bright sky at another result in a sharp loss 
of the resolving power of the lens. Consequently the optical system of the flight 
analyzer has been modified to overcome these generally poor photographic con- 
ditions. 
The general attack on the problem has been along the line of reducing flare 
lighting to a minimum to maintain 
  
s um s. 9806 - Som the contrast level as high as possi- 
‘9944 ^ —— 9886 . 9944" a MC pp P x ‘ +1 
Ti SS DENN ble. Because only a small portion 
/ à 9912-: of the negative is exposed at one 
/ Ki m time, it was possible to use a trav- 
I4: _9940 : : . : 
V / gunt pei | eling hood equipped with knife- 
i 9966. ^v \ edge baffles and masked by a 
| | curtain. The hooding system suc- 
| orncaL axs \ | | | | | || | cessfully excludes light from all 
| Sl | areas except the narrow vertical 
\ x e o d LEE field to be recorded, and good rec- 
FIG. 6. Distortion overlav chart. ords have been made under very 
adverse conditions. In one instance 
an aircraft flight was recorded successfully in a freezing sleet storm, with the 
light reading well below a Weston rating of 50. 
The fact that short exposure times are vital to the recording of rapidly 
moving targets has led to some lens modification. The minus blue filter and 
vignetted spatter filter, ordinarily incorporated in the Metrogon lens to reduce 
flaring in the center of the negative, cuts the effective lens speed by 4.5 stops. 
To reduce this loss of speed, a clear vignette, with a speed loss of only 2 stops, 
was substituted. 
THE SHUTTER 
The focal-plane shutter is composed of a slotted cylindrical blade oscillating 
behind a segment of a cylindrical surface incorporating a masking aperture. On 
either side of the shutter mechanism, and attached to it, are opaque curtains 
that extend to spring-loaded rollers on each side of the camera body. These 
curtains move with the shutter, keeping the plate constantly covered except 
for that portion which lies directly behind the shutter mask opening. 
As the shutter moves across the masking aperture it subjects the picture 
area of the film to an effective exposure of 1/3,000th second. At the same time 
a narrower slot in the same blade permits photographing the timer face at an 
effective speed of 1/6,000th second. 
The shutter oscillates through an angle of approximately 90° (45° on either 
side of the mid-shutter position). The mechanism is driven through a yoke by 
a pair of matched and diametrically opposed solenoids. Although the shutter