Exposure Compensation

[DarrenFrancis]

I, like many others, use exposure compensation on an almost daily basis to correct the exposure in my images. But how does it actually (technically) work? If you consider that you are not actually changing the aperture value, shutter speed or ISO, how does exposure compensation actually enable you to lighten/darken your images to get the correct exposure?

[GeoffWessex]

You're not (normally) changing the ISO with Exposure Compensation, but you'd certainly be changing the Shutter speed (if you're using Aperture Priority) or the Aperture (if you're using Shutter/Time Priority). Full Program modes may adjust both - and, with an Auto ISO set, may adjust the ISO for you. Try it out.... Set your mode as Aperture Priority and set an aperture of, say, 5.6, and choose a fixed ISO. With no Exposure Compensation set, read the values that you're getting - usually through the viewfinder or top LED - noting the Shutter speed. Now give it two stops of Compensation and look again at the shutter speed. Try it in other modes to see exactly what you'll get. The 'full' Program mode may change the ISO as well, if you're on Auto ISO (but you may not get feedback on this, depending on camera).

[DarrenFrancis]

Thanks for the response Geoff. I'll give it a go :-)

[chris-p]

Originally Posted by DarrenFrancis

If you consider that you are not actually changing the aperture value [or] shutter speed

As Geoff already said, you are changing these things. As for ISO, depends on the camera - on SLRs it generally won't in A (Av), S (Tv) or M modes.

Interestingly, if you shoot in full manual and use the exposure compensation feature it moves the indicator for a "correct" exposure - or at least it does on mine - so that when you select aperture and shutter speed such that the meter indicates it's correct it's still offset by the exposure compensation.