Once again, thanks to Claire for bringing this to our attention.
So, post-exposure latensification by low intensity light appears to produce better results than chemical latensification while permitting normal film development, possibly by a commercial lab. The drawback is the slight problem of doing the post-exposure itself if you donít have a darkroom. To date I have made my tests with in-camera latensification. This allows different amounts of latensification on each frame, but it is extremely time-consuming, especially as very long ultra-low intensity exposures seem to lead to less fog than shorter ones at a higher intensity. The Ďbetterí the reciprocity characteristics of the film, the more important this may be (I still have a lot of tests to do to satisfy myself that this is true). Iím also looking at the timing of the latensification exposure: how much do delays affect the result?
Patrickís circular affair with a central light didnít appeal to me, so I thought of another obvious way of doing it: take some square section drainpipe or other long box affair, arrange a simple film holder inside, make a long slot in the other side and cover it with a dense light attenuator made from layers of exposed, developed silver-image film. Itís designed for use without a darkroom, and to be as compact as possible.
Here are the rough details of the contraption Iíve started to work on.
The film is wound into the box on an endless belt of polyester film. The film leader is attached to the belt by a film clip that allows any misalignment to be accommodated. The tail end of the film is simply taped to the belt. A modified changing bag will cover the loading end of the box. The end of the box has an additional cover to use when the changing bag is open. The exposure itself is made in dim room light Ė possibly measured with a lightmeter.
I decided on the endless belt idea to prevent scratching of the film and to permit winding to be done from the loading end Ė inside the changing bag. If the box was big enough, and the belt wide enough, it could be used with sheet film. I've tested the film loading idea with a steel tape measure instead of a belt - this works well enough with 35 mm and is very simple, though a little awkward. A short 'axle' keeps the front end of the tape under control.