Test Report No. WCEFP-2-4, Physics Branch,
Sensitometry Unit 29 Nov 1951
Subject: Evaluation of 35 mm. Negatives


1. Four negative frames were submitted from the Air Technical Intelligence Center for photographic evaluation by the Sensitometry Unit. These negatives were exposed at approximately 2330 CST, 30 Aug. 1951, at Lubbock, Texas. The camera was the familiar Kodak 35 with coupled range-finder and a 50 mm (2 inch) f/3.5 Anastor Kodak lens. The Plus X film was exposed for 1/10th sec with lens aperture wide open, presumably with the camera hand-held and the film was processed in Panthermic 777 developer for 15 min. An interpretation of the configuration of spots was requested, in addition to general sensitometric notes.

2. A preliminary microscopic examination of the negatives disclosed the presence of patterns of spots, the patterns on the four frames being generally similar. Roughly 20 spots were visible on each negative in a flat "V" formation. In 3 negatives the formation consists of two rows, while the fourth shows all spots lined up in a single row. All negatives show evidence of camera motion during exposure, since the spots all are similarly blurred on the same negative, and the blur shape is different for each negative.

3. To resolve the formations and detect internal motion of the spots, each negative was examined on a large comparator microscope. The rectangular coordinates of each spot, relative to a convenient origin of coordinates, were read and then plotted on coordinate paper. It is emphasized here that the resulting plot is erect, but a mirror image, from left to right, of the actual object photographed.

4. Little significance, other than brightness variations, can be found from the negatives separately. When the charts were superimposed, however, it was readily apparent that the two rows of spots behaved differently. One row shows only slight variation from a precise "V" formation throughout, whereas the other row appears to pass from above the first row, through it to a position below. The spacings of this second row vary irregularly in the 3 frames plotted, while the first row holds a fairly precise formation. The first frame, No. 4, was not plotted because of extreme blurring, but frames 5, 7 and 8 were plotted as Charts I, II and III respectively. Chart IV is a composite of Charts I, II and III. In it the spots from the previous charts, that appear relatively fixed in the formation, are shown as heavy black ink spots. The relatively moving spots are shown in light pencil — the first position of these shifting spots is light red, as in Chart I; the second position, spaced between the heavy spots, is in black pencil, as from Chart II; and the final position is shown in light green.

5. According to the microscopic examination, spot brightness range could be expressed as weak, average, and bright, corresponding to faint, average, or heavy spot densities. The faint spots in the moving row are underscored, while the bright spots are circled. Only those spots in the fixed row that are alike in all three negatives are indicated in the same way.

6. There is the appearance of two extra spots, outside the regular rows. One spot is to the lower right in all three charts, while the spot shows only faintly in the No. 7 negative and was missed in plotting Chart II; it appears in position at the left end of the moving row in Chart III.


7. There is relative movement within the formation of spots, so that they are not lights on a fixed object. The relative motion is such that it appears unlikely that they are co-planar and photographed from different angles. Furthermore, it is unlikely that the moving spots are in any kind of straight line.

8. The angular size of the formation, at the camera lens, is very nearly the same in all cases. The formation is, however, slightly larger in Chart II, or Frame 7, than in the others. The angular size corresponds to an object size of 310 ± 30 ft., seen by the camera 1 mile away. The actual size of the formation may be calculated from this ratio, if the actual distance from the camera can be determined. This image size is actually 0.12", formed by a 2" focal length lens in the camera used.

9. Although the image size in Frame 8 is about 2% less than in Frame 7, suggesting that the objects are receding from the camera, the aspect of the "V" formation does not correspond to a horizontal "V", travelling parallel to the earth's surface unless at an enormous altitude. Such motion at conventional altitudes would require the "V" to flatten, eventually becoming a straight line, but the "V" in Frame 8 is a slightly smaller angle than in Frame 7.

10. The orientation of the "V" formation is the same on all negatives. If the formation did actually pass directly over the camera station, all photographs were taken either before or after, but not both. It is obvious that the image would be inverted on two successive negatives if they were taken on an approaching and then a receding slant angle.

11. The pattern of spot brightness is such as to prove conclusively that all 3 frames —5, 7 and 8—were exposed to the same object pattern of spots. However, the relative positions of these spots varies, as described above.


12. In the event that further assistance is required of this Laboratory, exposure tests should be made under identical conditions to determine the spot nature required to produce the observed densities, and to determine the amount of camera blur produced by an experienced photographer in "panning", to track a moving target at night.