Unit 57 – Photography Exposure

Correct exposure f:8 +3 stops f:2.8 -1 stop f:11 +2 stops f:4 -2 stops

Over exposed F:4 Correct exposure F:8 Under exposed F:16 Under exposed F:16 Correct exposure F:8 Over exposed F:4

There are three things that control exposure ISO – film speed Shutter speed Aperture

Film speed is measured in ISO 50 ISO film is used in very bright conditions and produces very fine-grain images 125 ISO film is used in normal conditions and produces fine grain images 400 ISO film is used when the light levels are low and produces grainier images How much more sensitive is 400 ISO film than 50 ISO film? 100 ISO film is twice as sensitive as 50 ISO 200 ISO film is twice as sensitive as 100 ISO 400 ISO film is twice as sensitive as 200 ISO 800 ISO film is twice as sensitive as 400 ISO

Shutter speeds are measured in seconds and fractions of a second. The film or sensor is exposed to light for the amount of time shown. This camera is set for This camera is set for 1/30th of a second 1/250th of a second

An exposure of 1 second lets twice as much light hit the film or sensor as an exposure of half a second An exposure of ½ a second lets twice as much light hit the film as an exposure of ¼ second ¼ of a second is twice 1/8th of a second 1/8th is twice 1/16th of a second and so on…

The aperture of the lens is measured in ‘f-stops’ which are written as f:8 etc. A one-stop change halves or doubles the amount of light getting through the lens f:22, f:16, f:11, f:8, f:5.6, f:4, f:2.8

An aperture of f:11 lets in twice as much light as f:16 f:16, f:11, f:8, f:5.6, f:4, f:2.8, f2

Shutter speed and aperture are linked – if one goes up, the other one must go down! Longer time Shorter time 1/8th f:22 1/15th f:16 1/30th f:11 1/60th f:8 1/125th f:5.6 1/250th f:4 1/500th f:2.8 Smaller aperture Bigger aperture

An exposure meter measures how much light there is at any given time– which lets you decide the combination of aperture and shutter speed you want to use to get the effects you want. Most cameras have one built in so you may have to do some mental maths!

Bracketing 3 stops over 2 stops over 1 stop over Correct exposure under 2 stops under 3 stops under 1/500th f:2.8 1/500th f:4 1/500th f:5.6 1/500th f:8 1/500th f:11 1/500th f:16 1/500th f:22