[MW Giles]

Interesting but the method used in RAF night bombers was simpler.

The photoflash was dropped with the first bomb and because of its ballistic properties trailed behind the a/c further than the bombs did. Therefore if the aircraft was flying level the actual flash would not appear on the film, just the reflections from the ground. The photoflash was on a time fuse, which like everything, was subject to an error. Rule of thumb was +/- 3.5 seconds at 20,000ft.

Once the camera control was activated, approx 8 sec before the flash was due to go off two new frames were exposed and wound into the camera magazine taking 3 or 4 seconds and leaving frame 4 to capture the image from the photoflash with an 8 second exposure time. Two more frames were then wound through automatically, hopefully getting the image of the flash from the bomb bursts on frame 6. The sequence was then repeated to ensure that frame 6 was safely in the camera magazine. The exposure time allowed for the error in the timing of the fuse.

The 8 sec length of exposure of each of the wanted frames (4 and 6) is why we get the fire tracks and swirling lights on the image from flak and search lights and the aircraft moving about.

If you want to read more there is a chapter in "Bomber Intelligence" by WE Jones, he was an Intelligence Officer in 1 Group

Regards

Martin