Push processingPush processing (extending the time the film spends in the developer) increases the contrast of the negative or slide. If you're shooting roll film, you pretty much have to push or pull the whole roll. But for sheet film shooters like Ansel Adams, it was a pretty good way to adjust contrast—terms like "N+1 development" in the Zone System refer to this method of adjusting contrast. (You also have to know, prior to development, whether you want to increase the contrast. That sort of planning was Adams' forte.)