Polaroid Type 612

Type 612 was the fastest film Polaroid ever sold, and probably the fastest commercial film any manufacturer has ever sold. The ISO 20000 rating was not marketing exaggeration. It was the actual working sensitivity, set so the film could record an oscilloscope trace during a single shutter release. You pointed a Polaroid pack camera at a CRT, fired the shutter, peeled sixty seconds later, and had a permanent record of the waveform.

The trade for that sensitivity was contrast. Type 612 was brutally contrasty, with effectively no midtone region. Phosphor traces on a dark scope screen are exactly the subject the curve was tuned for: a bright stroke on deep black. Pictures of anything else came back as caricatures. Shadows blocked instantly and highlights paper-whited just as fast. The few photographers who tried it for night street work reported the results as curiosity rather than keeper.

Production ran from 1981 through 1997, with the film off Polaroid's catalog by 1998. The customer base was engineering laboratories, hospital ultrasound and EKG departments, and physics research facilities running spark chamber work. When digital scope storage and thermal printers took over the recording role through the 1990s, demand collapsed and the film went with it.

Format was 8.5 by 10.8 cm pack film, ten exposures per pack, for the Polaroid CB-100 and similar instrument cameras. Compared with the common Type 667 at ISO 3000, the 612 sat almost three stops faster while losing essentially all the latitude that 667 retained. If you needed to capture a transient single-trace event with no opportunity to retake, only the 612 had the speed.

Reciprocity exponent is 1.0. Zone Light Meter applies the correction past one second, though almost nobody exposed Type 612 past a tenth of a second in actual use. The film was designed for shutter speeds in the millisecond range. If you find a pack in a lab cabinet today, the emulsion is almost certainly fogged, but the pull-tab mechanics still work.