I often times get asked which exposure mode I shoot in and why. My answer is, it depends. I prefer to shoot in M mode and Av mode. So how do I decide which mode to shoot in? Simple. If the lighting is consistent, then I use M mode. Otherwise I prefer Av mode. Let’s elaborate on that a little more.
Typically, the camera’s built-in exposure meter will try to expose the scene in neutral gray. This is what the camera thinks is what a typical exposure should be. This is how it sees the world. Of course in the real world, things are often times not so nice and neutral. This is why you often times read when shooting something bright, like snow, your camera will tend to underexpose the shot because it thinks it is going to overexpose the shot relative to neutral gray. The opposite is true for something dark, like a tuxedo, where your camera will tend to overexpose the shot because it thinks it is going to underexpose relative to neutral gray. So the camera doesn’t necessarily know best and it’s bad practice to chase the exposure meter to the middle. You, as a photographer, will need to make an educated decision whether to purposely under or over expose a scene relative to what the camera would think is the correct exposure. So this means if a white wedding dress is dominating the frame, then you need to over expose by at least 1 stop, probably more. If a black tuxedo is dominating the frame, then you need to under expose by at least 1 stop, probably more.
As far as which exposure mode to use, When the lighting is consistent, such as under overcast skies, I don’t want things that are very bright (wedding gown) or very dark (black tuxedo) to affect the exposure. Think about that for a moment. The light level hasn’t changed. If I am in Av mode, the camera’s exposure meter will be easily fooled and will either underexpose (white gown) or overexpose (black tuxedo) the image. In M mode, I know the exposure will be consistent regardless of the brightness/darkness of the subject. This also helps when processing the images since I know any adjustments in exposure values can be applied across the series in a batch, saving me lots of time.
Another thing I see a lot and something I touched on earlier is that some folks shoot in M mode but work very hard to get the exposure needle to the middle. This defeats the purpose of being in M mode because by doing this, you are still allowing the camera to make the decision when it comes to exposure. So essentially you are still letting the camera completely dictate what the correct exposure is. The correct way to approach it would be to take a look at the scene and try to figure out whether you need to under or over expose relative to neutral gray and adjust the aperture and shutter speed accordingly. This way you are in total control of your exposure!