(Hapo 66-E, Ilford Delta 3200, EI 1600/33°)
One of the things photographers and enthusiasts have to worry about is ISO speed, which together with aperture and shutter speed, is one of the three variables that control exposure. In digital cameras, the ISO rating is adjustable from shot to shot, and determines how sensitive to light the sensor is. In a film camera, the ISO speed is a property of the film, not a camera setting. That's why it is properly called film speed.
If you have a digital camera and want to take a shot in low light, one of the possibilities you have is to choose a high ISO speed, in order to make you sensor more sensitive to light. This way, you might be able to achieve a shutter speed fast enough to shoot hand held. With a film camera, you choose a fast film. Since there ain't no such thing as a free lunch, though, high ISO comes at a price: noise with digital cameras, grain with film. It is a matter of taste and depends on the picture but, in general, grain does not bother me that much. Digital noise is another matter, though. I guess grain, especially on black and white film, has a kind of journalistic quality about it that makes it look familiar.
If your film is not fast enough, you always have the option of push processing it. This is easily understood with an example: I am shooting a film with a nominal ISO speed of, say, 100. But I expose it as if it were an ISO 400. This is called film rating, I rate my film to be ISO 400 (in fact, you cannot talk about ISO any more, but of exposure index, EI). I am getting a consistent underexposure on all my shots (they would be all too dark). But, since I know that, I let it develop (and here comes the push processing) for a longer time than a normal ISO 100 film would require.
This picture comes from the first film roll that I let push process. It is taken on Ilford Delta 3200, which despite the name is an ISO 1000 film, but I rated it at EI 1600. I let my photographic lab push process it, but I am not that happy with the results, which came out a little too dull. I guess I would be happier having the whole thing under control, or at least I would have much more fun...
I am beginning to consider facing the ultimate challenge: black and white film development at home.