Reddit reviews How To Photograph an Atomic Bomb

There's actually at least one book out there, called How to Photograph an Atomic Bomb that describes the process. With the proper shielding (heat shields, lead shielding to prevent the radiation from the explosion screwing up the film) and shock-absorbers, it's not that difficult. What's trickier is getting the cameras and equipment back after the explosion when they're contaminated by radioactive waste.

Rapatronic shutters operate on the basis of polarized glass whos polarization depends on the flow (or lack of flow) of electricity through it. Two sheets of polorized glass are placed in front of the film medium. The polarization of these sheets are 90 degrees from one another and so no light is able to reach the film medium to expose it.

I forget what the exact mechanism at play is, but at the moment of shutter release an electrical impulse is sent to the front sheet of glass, altering its polarization to be in line with the second sheet of glass. This allows light into the camera and onto the film medium.

Because electrical impulses can be exposed to a much higher degree of accuracy than mechanical shutters, this enables exposure times of 1/1000000 second and shorter. To achieve multiple frames, they simply set up multiple cameras. There is no way to spin a mirror fast enough to capture those speeds.

Source: "How To Photograph An Atomic Bomb", a wonderful book about Harold Edgerton, who invented both the rapatronic camera and the modern electronic flash.

Edit : link formatting

Not in these tests; Copying and pasting again:

In these shots, the cameras were encased in 2.5" thick Lead boxes, mounted on poles, and secured with guy wires (wrapped with foil). The cameras they used inside the houses were also encased in 2 inches of lead shielding, and were bolted to the foundation.

The cameras used to captures these tests were called GSAP cameras, (Gun Sight Aiming Point cameras), which were handy for this operation, since they were small and reliable. The power boxes for these shots were buried underground, and hooked up to a timing operator, which turned on the cameras when the bomb went off.

The tests you're thinking of, where they used mirrors, were the hydrogen bombs and Megaton yielding bombs that were usually tested over the Pacific (See; Casle Bravo).

Source: Peter Kuran's How to Photograph an Atomic Bomb book

Picture of one of the camera boxes used in these tests

For more information on how these tests were photographed, please refer to this PDF file, which documents their techniques, strategies, and goals accomplished in the photography.

For those interested, this is an excellent read!