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Frequently Asked Questions
Push and Pull Processing
What is push and pull processing?
Push processing is a technique used by photofinishers to produce acceptable results from a film that has been exposed in a camera (either accidentally or deliberately) at the wrong speed (ISO).
A film generally produces the best results if the camera is set at the ISO number recommended by its manufacturer and processed normally. However, sometimes there isn't enough light to use a film at its rated speed. Doing so might force the photographer to use an extremely slow shutter speed, resulting in blurry pictures. If it is not possible to use a higher speed film, one solution is to underexpose while taking the picture and then give the film more development time than is normally recommended. (This requires an adjustable SLR camera.) For example, the photographer may shoot a film rated at ISO 100 with the camera set at ISO 400, allowing his/her camera to use a faster shutter speed. It is important to be aware that while doing this will capture the image, it will also result in a poorer quality in tone reproduction and an increase in graininess in the final print.
Black-and-white negative films and color reversal films can be push-processed; most color negative films can not be usefully push-processed.
Pull processing is basically the same procedure in reverse: shooting a film at lower than its rated speed. The photofinisher compensates for the incorrect exposure by giving the film less development time than normal.