Push Processing
Rating a film above its nominal speed and extending development to compensate.
Measured in
stops
In depth
Pushing does not truly increase sensitivity — the shadows receive less light and stay thin whatever the development. What extended development does is raise contrast and build density in the midtones and highlights, producing a usable negative from an underexposed one. Grain becomes coarser and shadow detail is permanently lost.
Examples in practice
A 400-speed film shot at 1600 and pushed two stops yields printable negatives from a dim concert, with heavy grain and empty shadows.