Apr 03, 2018 Written by Pawan Negi Exposure
1.In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance.
2.Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.
3."Correct" exposure may be defined as an exposure that achieves the effect the photographer intended.
4."Manual" exposure calculations may be based on some method of light metering with a working knowledge of exposure values, the APEX system and/or the Zone System.
5.An approximately correct exposure will be obtained on a sunny day using ISO 100 film, an aperture of f/16 and a shutter speed of 1/100 of a second. This is called the sunny 16 rule: at an aperture of f/16 on a sunny day, a suitable shutter speed will be one over the film speed (or closest equivalent).
6.An important principle of exposure is reciprocity. If one exposes the film or sensor for a longer period, a reciprocally smaller aperture is required to reduce the amount of light hitting the film to obtain the same exposure.
7.The Zone System is another method of determining exposure and development combinations to achieve a greater tonality range over conventional methods by varying the contrast of the film to fit the print contrast capability.
8.Today, most cameras automatically determine the correct exposure at the time of taking a photograph by using a built-in light meter, or multiple point meters interpreted by a built-in computer, see metering mode.
9.Areas of a photo where information is lost due to extreme darkness are described as "crushed blacks". Digital capture tends to be more tolerant of underexposure, allowing better recovery of shadow detail, than same-ISO negative print film.
10.An exposure meter may not always be available, and using a meter to determine exposure for some scenes with unusual lighting distribution may be difficult.However, natural light, as well as many scenes with artificial lighting, is predictable, so that exposure often can be determined with reasonable accuracy from tabulated values.