Pushing and Pulling Film

Pushing film or push processing is where a photographer programmes the speed of their film to faster than the speed indicated by its ISO / ASA label. For example an ISO 100 film can be pushed when the camera is programmed to treat it as ISO 200 or 400 film.

It can be necessary to push film if one has film that is not suited to the available light conditions. Film can be pushed to a faster film speed so that it may be used in lowlight conditions. The whole film will have to be used at this setting and pushing film does result in the whole film being underexposed. Increasing film speed from ISO 100 to ISO 200 will underexpose each frame by 1 stop. Therefore in order to get the film developed correctly for it exposure it is necessary to instruct the processing lab of the amount of stops that the film has been pushed by.

Pulling film is the opposite of pushing film and is useful for correcting film speed that was accidentally rated at a higher speed.