Push processing

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Push processing is a term from photography, referring to a development technique that increases the speed of the film being processed.

Push processing involves developing the film for longer, and/or at a higher temperature. This allows larger grains of silver to form in the emulsion, forming a darker negative. This results in a lighter print and hence an increase in the apparent film speed. The opposite of push processing is called pull processing, which decreases the speed of the processed film. It is achieved by developing the film for a shorter time, and/or at a lower temperature.

Push processing is more popular than pull processing as photographers usually want to make a film faster, not slower. As such, the term push processing is sometimes used as a generic term for both push processing and pull processing.

By push processing film, the film can be exposed at a higher exposure index (EI) than the manufacturer's indicated film speed, allowing the film to be used under lighting conditions that would ordinarily be too low for good exposures. However, this comes at the cost of decreased quality: artifacts such as higher contrast, lower resolution, distorted colours, increased grain, etc. are often visible on film that has been push processed. Often, film is push processed to create these artefacts as part of an artistic effect. When a film has been push or pull processed, the resulting speed is called the EI, or exposure index; the film's speed is always the manufacturer's indication. For example, an ISO 200 film could be push processed to EI 400 or pull processed to EI 100.