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Image on film plane
Rotating mirror
:rir_"iiiirr."_T:
-Object
First lens
^Second lens
Fig. 7. Schematic diagram of the optical system of the 100,000,000 frame/sec camera.
is formed through the multislit focalplane shutter which is in intimate contact (optically) with the photographic emulsion. The parallel slits in this shutter are 0.0002 in. wide and are separated by opaque spaces of 0.020 in. A single exposure of a spherical explosive charge taken through this shutter is shown in Fig. 6. It should be noted that this picture resembles the image on a television screen in that it covers the full picture size, but only a fraction of the total area is involved in the image formation (1% for the shutter described above). If the shutter is now moved one slit width the first exposed image is completely covered and unexposed film, on which a second picture can be formed, is uncovered by the narrow slits. One hundred independent exposures can be formed with only 0.020 in. of motion of the shutter described.
In order to photograph an event at the rate of 100,000,000 frames/sec the shutter is required to move 20,000 in./sec. Since it is not feasible to move the shutter mechanically at this speed and still hold it in intimate contact with the film, as required to overcome the deleterious effects of optical diffraction, a rotating-mirror system as shown in Fig. 7 was employed. With this arrangement a 20-in. optical arm and a mirror velocity of approximately 100 rps produces 100,000,000 frames/sec. An accurate 1 : 1 image of the grid is formed at the film plane so that when the corn
Fig. 8. Exposed plate of shock from pentolite sphere taken with the ultrahigh-speed camera showing complete exposure and selected single frame.
plete record of superposed images is obtained with this camera a single frame can be selected by the proper placement of the multislit shutter back on the exposed plate as shown in Fig. 8.
Morton Sultanoff: Study of Explosives
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