F/stop

Stop

Photopedia

23 October 2007 15:02

A stop is an expression used to specify an amount of exposure without necessarily stating the shutter speed or aperture. Each stop either halves the amount of exposure given (-1 stop) or doubles it (+1 stop). You’ll find it most commonly referred to when using the exposure compensation function, where you can alter the exposure suggested by the camera by whole (or fractions of) a stop.

This exposure compensation will affect either the shutter speed or aperture. In terms of shutter speeds it’s not too difficult to work out – if your starting shutter speed is 1/250sec then -1 stop is 1/500sec and +1 stop is 1/125sec.

Things are a little more complicated when you start talking about apertures. Due to the strange numbering system it may take a little while to remember the actual values, but here is how it works. It’s easiest to remember that for every 2 stops the aperture value either halves or doubles. So if you start at f/8, -2 stops is f/16 and +2 stops is f/4.

For single stops you use the intermediate numbers, again using f/8 as a starting point, so -1 stop is f/11 and +1 stop is f/5.6. For a list of the full aperture values, take a look at this graphic (aperture settings).