Hypering, sensitising, preflashing...

Ok, everyone knows you can't increase the shadow speed of film by developing longer or with different developers. Such things can only make a small difference in shadow speed.

So, what techniques REALLY increase film speed? Does preflashing really increase shadow speed, that is, is the phenomenon of film emulsion 'inertia' real, or does preflashing just add base density? What kind of crazy concoctions can be used to sensitize film? What effect does cryogenic temperatures have?

Cryogenic? Film hypering is done with a mixture of hydrogen and nitrogen at about 50 degrees C IIRC, anything but cryogenic.

How much can it increase the film sensitivity?

I have no idea, I have only read about it some time ago and everybody seemed to use these gases and some kind of thermostat to keep film heated at specific temperatures.

There is little to no advantage with "gas hypering" and more modern films. It began to fall out of favor in astrophotography (where it was by far the most widely used) about two decades ago. The company that was formed to serve this market with equipment (heated pressure chambers, etc.) no longer produces anything related to film hypering, and my possibly be out of business or the name of the business sold.

Lee

What is your application?

Indeed hypering fell out of favour some time ago for various reasons. You can still do it of course, but what most astro types do now is stack images. There is excellent software for that. You could also stack negs by hand in order to achieve more or less the same effect, but registry will be a challenge and the exposures will get quite long if you have a lot of negs! The most I have done was two and that was for a 5x7 contact print. If you do it electronically then it is easy.

So for example you can shoot at whatever ISO you need, even if it is quite high, and reduce the noise/grain by stacking the images. The film grain is random so it will average out to smoother tones, whereas the real information is not random and will emerge more clearly. With this technique it should be possible to, e.g., shoot the moon at ISO 3200, stack ten frames or so, and get excellent tonal detail with almost no grain at all. Of course, the big fly in the ointment is subject motion, but if you simply align the subject from frame to frame...

A contributor whom I haven't seen here for some time uses Imagelink HQ and as a routine uses a perborate bath before development and before that 'flashes' the film with a dim green safelight at 12' for 30 mins.
Claims to get a good EI 0f 50 and smooth tones.
The theory is that it takes 3 photons to sensitise a crystal of the silver salt to a developable state. The flashing and hyper bath supply more photons which scarcely affect the highlights but bring up detail in the shadows where photons are scarce.
Murray

Later ; I found a thread here
(there was a url link here which no longer exists)