Thanks Ian for an excellent article. You made the general principle very clear. However, I do not believe that there are many bird photographers who use the full matrix option for exposure of birds. I never do. I much prefer the single point AF, which means that you are only exposing for a portion of the bird's body. To do this you have to get in very close of course, which I almost always achieve. What do others think of my observations here?

Hi Keith

Thanks for drawing my attention to this article. I had not yet noticed it had been published.

I am not sure what you mean by 'single point AF' in the context of exposure. Cameras don't necessarily link exposure sensor to focus points. With my Canon camera, Matrix metering is a 'smart' mode which attempts to link exposure readings to (amongst other things) the areas of the scene which are in focus (which would be indicated by the relevant squares or other focus indicators in the viewfinder). However the camera still measures an average across the whole frame; it simply uses the focus points to decide which areas of the scene to give priority to in determining that average (it assumes that you will focus on the important things). Centre weighted metering, in contrast, always gives weight to the centre of the image. It measures an average of the light across the scene, but rates the centre of the image slightly more highly in determining that average. It uses the centre of the image regardless of where you focus.

Perhaps you mean the third metering option - spot metering. In this case the metering is only done in a small area of the centre of the scene and the rest of the scene is ignored. However, again, in my Canon camera this does not 'follow' the focus point. If you use a single focus point, you can shift that around the viewfinder if you want to focus somewhere other than the centre of the image, but the metering spot does not shift with the focus point. It always stays in the centre. Your camera (Olympus?) may do this differently.

If you do use spot metering, you still need to be aware of the 'middle grey' issue. Your meter will still give you a light reading that assumes you want middle grey. So if you place the spot on a white bird, you will need to overexpose a little to ensure the bird comes out white, not grey. Likewise if you place your sport on a black bird, you will need to underexpose to ensure that it remains black.

Cheers
Simon