One of the great things about most “modern” black and white films is that they have a wiggle room for making an exposure. Photographers have learned to exploit this wiggle room in order to shoot their film at higher shutter speed by rating the film at a higher ISO then box speed. But like all things in life and photography this is no free lunch sacrifices are made.
Any given film has a range from light to dark from which it can capture an image. Ansel Adams illustrated this with the zone system. When you push a film (i.e. shoot it at a higher rated speed) you compress that range between what is commonly called the toe and shoulder. By compressing that range you create more contrast between black and white because the tonal graduation between the two becomes steeper and less gradual. When you’re working with a negative the size of a 35mm frame this compression can become downright ugly. To use Ansel Adams expression, it can become chalk and soot meaning all the detail is lost. Sometimes this can be used to artistic effect but in landscape photography it’s generally undesirable. It also can make grain more pronounced, again, when used in the right setting that grain can create a mood and sometimes that’s desired, but often it just becomes an ugly distraction that takes away from an image rather than compliment it. When printing on paper which is normally higher contrast then a negative to begin with the loss of detail is normally worse. With today’s scanners and post processing software however you can make some adjustments and save some of that detail.
Pushing film is really very simple to do and sometimes you have a choice of either pushing your film or not taking the photo at all. For example, the first picture in this article was taken wide open with a fast lens using available light. At 400 iso my shutter speed would have been so slow that the images would not have been as sharp because of camera shake and the motion of the musicians. When your subject is a moving target or you don’t have a tripod pushing your film can be your only option. To push film you simply rate it at a higher speed in your light meter (or your brain if you’re not using a light meter). By adding 2 stops to your shutter speed or if you’re goal is to increase your depth of field stopping down your aperture. If I confused you with the term stopping down it simply means closing the aperture two stops (i.e. going from f2.8 to f5.6). At this point you shoot normally and then if you’re smart you’ll use a sharpie to write the film ISO on the canister or roll of film when you’re done so that when it comes times to process it you remember that you have to do things a little differently.
For the most part to push your film in the development process requires you to either extend development time or increase your temperature. There are some developers that do not require this such as diafine but I’ll save that for another article at this time since I have no experience with it. A good guide to start with is with the massive development chart found at Digital Truth.
Chances are if you can dream it someone has tried it and posted the results there. This is just a starting point however and you can tailor your times and temps to get your own desired results. The beautiful thing about photography is that there really isn’t a right or wrong way to do things, there is only a way that achieves the best results for you. We all have different tastes and our own tastes evolve over time. Personally I like high contrast and I use this technique regularly.