>>3425322The other way round.
If you want to push, say an ISO400 film, you set the camera *higher*, say to 1600. The camera will think the film is ISO1600, giving it less exposure (faster shutter for instance), and you end up with underexposed film because it was actually ISO400.
To "compensate" for that, you develop the film for a longer time, to make up for the underexposure. The *real* gain is usually a bit less than a stop, with a good pushing developer. After that point, only the midtones and highlights get brighter, the shadows remain dark, that's why pushing increases contrast. Still not a bad look, if you like it.
People are always hyped about pushing, but *pulling* is actually much more interesting, and you get many benefits.
You set the camera to a *lower* ISO than your film, resulting in overexposure, and then you compensate for that by reducing developing time.
The way film works is, overexposing mostly brightens the shadows, and overdeveloping mostly brightens the highlights. Underdevelopment mostly "darkens" (=keeps in check) the highlights.
So by overexposing and underdeveloping, you brighten your shadows and keep your highlights from blowing. This increases the dynamic range (you can capture a very contrasty scene), and the extra exposure + shorter development reduces grain. Very interesting look, and the negatives are a pleasure to work with. (Most large format B&W landscapes use this technique extensively).
So in short
>Pushing: rate the film higher, develop longer, get more contrast and grain>Pulling: rate the film lower, develop less, get less contrast and grainAnd yeah you tell the lab how many stops you want it pushed or pulled.
Mind you, this only works with B&W film, because for colour, each colour-sensitive layer responds differently to pushing (say, blue pushes more than red), so you get colour casts when pushing. Also, the process is standardised, so you don't have any special pushing developers, just the standard CD-4 based one.
