Varying the development process - such as using a different developer - can also affect the quality and speed in similar ways. This means that slow film can generally produce higher quality results than fast, but this must be balanced against the motion-stopping and depth of field available from fast films. It is common for fast film to have larger grain size and poorer rendering of colours (or grey scale) than slow film. Increasing the speed of film this way is called 'pushing' decreasing the speed of film is known as 'pulling'. changing the development times, temperature, chemical dilution or using different developer chemicals provides the photographer a choice of a range of speeds for any given film. The speed of a film is specified for a particular, standard method of processing. 'Slow' film - say, speeds below 100 ISO/ASA - can be used for slow shutter speeds - for deliberate blurring of motion, or large apertures to give small depths of field for selective focusing. In other words, fast films can result in sharper pictures. 'Fast' film is more sensitive than average - typically with speeds of above 400 ISO/ASA - permitting photography in low light, or the use of high shutter speeds and small apertures, allowing freezing of motion (and reduced camera shake), or large depths of field. There are currently two numbering systems in use - ASA/ISO and DIN, but there have been various other predecessors. Film speed is represented on a numeric scale on most scales, the higher the scale number, the less light that is required to expose the film. 'Faster' film requires less light, and so can be exposed at a faster shutter speed or smaller aperture. Speed is a measurement of how much light is needed to make a usable image on light-sensitive material such as film - in other words, a measure of sensitivity. 3 Arithmetic v Logarithmic (Log) scales.

Din to iso conversion