The ABC of Photography – ISO

Stands for International Organisation for Standardisation. In photography, it refers to a system for measuring and specifying the sensitivity of digital imaging systems and photographic films. The higher the ISO number, the greater the sensitivity to light.

Cameras have an ISO range, enabling you to choose an ISO setting that suits the situation in which you’re shooting.


The ABC of Photography – Inverse square law

This law particularly relates to the use of studio lights or flash and says that if an object is twice a particular distance from a point source of light, it will receive a quarter of the illumination. For example, if your subject is two meters away, and you increase it to four meters, the resulting fall-off means you’ll need four times the amount of light to keep the same exposure settings. Alternatively, you’ll have to increase the exposure by two stops.


The ABC of Photography – Infrared photographs

mages recorded on an image sensor or photographic film that’s only sensitive to infrared (IR) light, beyond the spectrum visible to us. Black-and-white IR landscapes have a ‘dreamlike’ quality’; grass and foliage are recorded as almost white, while blue skies become black. Digital cameras can be converted to only shoot IR images by removing the IR blocker in front of the sensor in the camera body and replacing it with a filter that instead blocks visible light.


The ABC of Photography – Infinity

Optical term to describe objects that are so far away from the lens that light from them reaches the lens as parallel rays. In practice, it’s usually used to mean objects that are on or near the horizon. Represented on lenses by the mathematical symbol, ∞.



The ABC of Photography – Image sensor

An integrated circuit chip that converts an optical image into an electronic signal. In current digital cameras, most are either CCD (charged coupled device) or CMOS

(complementary metal-oxide-semiconductor) sensors.

CCD sensorCMOS sensor



The ABC of Photography – Image file format

A standard way of encoding information for storage in a computer file. File formats used in photography include JPEG, TIFF, PSD and GIF, all of which are suitable for particular uses. See the separate entries for those formats for details of how they differ.