267 "ec 
REPORT OF COMMISSION V GV-99 
The entire room is darkened. Unexposed film is advanced into position. The 
trans-illuminator is turned on to make the exposure of the grid. After sufficient 
exposure, the trans-illuminator is turned off. The film is advanced. The re- 
quirement of darkening the room would not be necessary if the shutter included 
"bulb" or “time” setting rather than being fixed at 1/50 second. 
The same procedure is repeated for a scale setting of 2. However, one addi- 
tional step is required, and that is an intentional double exposure of an object. 
After the grid is exposed for a scale setting of 2, the film is not advanced but an 
object 6 millimeters high is placed on the grid and is exposed with the annular- 
illuminator (Figure 1). This illuminator is turned off after a sufficient exposure. 
The film is advanced and the room light turned on. The double exposure pro- 
cedure is similar to the technique used for years by still and motion picture 
photographers for special effects. The film is removed from the camera and 
processed. 
a) Determining the focal length: 
1) The measured distance be- 
tween points a; and b; (Fig- 
ure 2) on the right negative 
of stereo-pair No. 1 is 25.05 
millimeters. 
2) The measured distance be- o d 
tween corresponding points 
A, and B, on the grid is 
25.00 millimeters. 
Ld > 3) The scale of the negative 
ab, 28.25 Fic. 2. Point designation for Stereo-Pair No 1. 
m = = 1.010. 
a > AH, 25.00 
4) Repeat steps (1) and (2) above for stereo-pair No. 2 (Figure 2). 
5) The scale of the negative is 
sho 19.25 
S» — = = 1.925. 
ABs 10.00 
6) The measured distance (Ad) between the indices 1 and 2 on the scale 
plate is 83.4 millimeters. 
7) The focal length of the Stereo-Camera optical system is 
Ad 83.4 
f = = 91.1 millimeters. 
Se — Sy 1.925 — 1.010 
b) Determining the photo-base: 
1) The object distance for stereo-pair No. 2 1s 
1 1 
D = (( À ) = 01.1 (1 + ) = 138.4 millimeters. 
S» 1.925 
2) The differential parallax (Ap) between the grid intersection c and 
the top of the object n (Figure 3) is measured with a stereometer and 
found to be 1.60 millimeters. 
3) The height of the test object ) is measured with a micrometer and 
found to be 6.00 millimeters.