Meter me this?

[Texas Dave]

After the back button discussion not long ago, some points were brought up that helped me understand some of the problems I've been having with metering.

I was using the back button focus, reframing and didn't realize I was metering on the half pressed trigger. I thought I was metering along with my focus, which when using spot meter on white egrets in ponds, I was getting blown out birds. Now I know why.

So now I have my back button focus button and then I have my AFL-AEL button assigned to AEL on release. An extra job for my thumb, but I can now focus, meter on what I want to and then reframe. (don't call me stupid, it works for me...at the moment.)

Anyway, my question is, does auto WB work in conjunction with the metering? If I matrix meter for exposure does the camera use the same matrix area to WB? If I use the only the spot meter does the camera adjust WB to match the color of light just in the spot area being metered? Just wondering?

[Polar01]

Dave I do not know, however if you are shooting raw files then who cares what the WB is as you adjust it to your liking in post production. One problem as I see it is if you use spot exposure on the white egret and lock it, then the overall image will be underexposed. This is because the metered white egret, will be set for middle grey thus the overall image will be underexposed you could correct this by using compensation, now if the egret is a BIF and the sky is brighter than the bird then yes to your method. Any which way if shooting raw files then who cares what the auto WB is as you can adjust in post.

Cheers: Allan

[xpatUSA]

After the back button discussion not long ago, some points were brought up that helped me understand some of the problems I've been having with metering.

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Anyway, my question is, does auto WB work in conjunction with the metering? If I matrix meter for exposure does the camera use the same matrix area to WB? If I use the only the spot meter does the camera adjust WB to match the color of light just in the spot area being metered? Just wondering?

I think not. The white balance is applied to the whole image. For simplicity, think of three multipliers for red, green and blue being applied to every pixel in your image (after de-mosaicing). Now, again for simplicity, "auto" assumes that the average hue of your image is neutral and calculates those three multipliers based on that assumption. It's called the "gray world" algorithm. (However, if the scene has large areas of one color, the calculation usually fails and your image will have a color cast). There are much more sophisticated algorithms - too complex to explain here.

[Mike Buckley]

if you are shooting raw files then who cares what the WB is as you adjust it to your liking in post production.

The less I have to do during post-processing, the better. Also, the more accurate the exposure, the less noise is produced. White balance affects exposure even if only slightly, as is evidenced by the change in the histogram resulting from a change in the white balance.