Why do they have exposure compensation

[swoosta]

Why do they have exposure compensation on cameras. If its the same as increasing or decreasing the stops why not just use the shutter speed or aperture. What's the difference?

[silversnapper1]

Camera meters are never 100% accurate and exposure compensation is used in Aperture Priority and Shutter Priority to adjust over or under exposure where the camera metering is fooled by maybe an over abundance of a particular colour say black or white in the image.

[swoosta]

why don't you just compensate using the shutter speed or f stop

[silversnapper1]

Because in Aperture Priority you set the aperture and the camera sets the shutter speed and in Shutter Priority you set the shutter spped and the camera sets the aperture. Therefore, depending on the light metered by the camera can over or under expose the image so you need to have some sort of redress to balance the image.

[Cathus]

You only use exposure compensation in the auto / semi-auto modes eg Aperture or Shutter Priority because the camera sets one while you set the other. The exposure compensation tells the camera to adjust what it thinks is the correct setting.

Of course in fully manual settings you don't have exposure compensation because you set both shutter & aperture.

If you always shoot in manual then exposure compensation is irrelevant.

[nikonian]

To put it simply, meters are a bit stupid, they think they are always looking at 18% grey. About the worst case is pure virgin snow, which requires about 2 stops more light.

[OldBoy]

Originally Posted by Cathus

If you always shoot in manual then exposure compensation is irrelevant.

I beg to disagree, exposure compensation is used where you need a faster shutter speed, but the scene dictates a slower one.

[KeithT]

Exposure compensation is totally different from raising ISO. What the camera's metering system does is to take readings from various parts of the image and set a blanket average based on 18% grey. Most times this is fine and you get a useable exposure. Setting higher or lower ISO's will not prevent the camera from giving you this blanket setting.

In tricky lighting conditions exposure compensation adjusts the blanket exposure to take into account other factors, like harsh white walls against a darker foreground or background (simplified explanation) where you may need to open up the exposure because the camera has been fooled to close it down by that amount of stops because of the harsh light of the wall; or give a minus compensation because the camera has been fooled to open up too much because of a large area of dark.

One way round exposure compensation is to use exposure lock. Just find an area of midtone like grass or anything between the shadow and highlight and lock your exposure on this before composing and taking the picture (the lazy way). I often use this method, although being able to compensate using the wheel dial on the back of my camera is just as quick these days.

Remember, you are not upping ISO when you are using exposure compensation; you are overriding/tweaking the camera setting which may not be perfect.

[Cathus]

Originally Posted by OldBoy

I beg to disagree, exposure compensation is used where you need a faster shutter speed, but the scene dictates a slower one.

I don't follow this, exposure compensation settings are to override what the camera sets (either aperture or shutter) but in manual the camera doesn't set aperture or shutter so how can it override them?

[chris-p]

Originally Posted by Cathus

I don't follow this, exposure compensation settings are to override what the camera sets (either aperture or shutter) but in manual the camera doesn't set aperture or shutter so how can it override them?

I'm not sure if this is what OB means and I don't know the specifics for Canons but with Nikons, if you set exposure compensation in manual mode it treats adjusts metered 'zero'.
It's not overriding the camera of course but it does have an effect. Dial in -3 stops and shoot in manual at a metered "correct" exposure and you're -3 stops below...