www.ukbutterflies.co.uk

A question for the photography experts: I have a Canon 20D and generally use Partial metering as it seems best for dark butterflies on a lighter background. So I have no real problem in the field.

However, I recently tested a dark subject on a white background for all three modes – as described in the manual page below – and found that:

1. Partial metering was best i.e. the subject at the centre appeared correctly exposed (more or less).
2. Evaluative metering had the subject slightly, but not greatly, darker than Partial.
3. Centre-weighted average (CWA) had the subject very much darker.

This is not what I would have expected, which is that CWA would have the centre subject slightly darker than Partial, and Evaluative would have been much darker (because it is metering over the whole area and most of it was a white background). CWA is in effect a half-way house between Partial and Evaluative metering, is it not? But this is contradicted by results.

Also, I am dubious about the symbols used. I would have thought that Evaluative would have been shown by an empty box, not by a symbol with a heavy black dot in the brackets suggesting a strong focus (sic) on the centre. I would have expected the Partial to be shown by the heavy black dot but, it is just the “empty brackets”. And CWA I would have expected to be the empty brackets. Or am I missing something here? The darkest result would be expected from Evaluative metering and this matches with the empty box icon, except that it is described as CWA.

I feel sure Canon could not have got it wrong, but can’t seem to square this with the test results. Anyone who can throw any light on this (sic) would be greatly appreciated.

Roger
I reckon your results are just about as Canon have suggested, and I would have guessed at myself.
You have set up one of the most difficult situations for a photograph.
Centre Weighted Average takes into account a lot of the scene that is not dark. Thus it will tend to underexpose to try to balance out to mid-grey.
Evaluative metering will also struggle here, and at the end of the manual section it suggests, if the contrast is high, using-
Partial Metering, which is effectively Spot Metering over a slighter wider area.
It is the mode my 20D and 30D are left in by default.
HTH
Roger

Thanks, Roger. I don't quite understand it (i.e. why Evaluative was not as dark as Centre-weighted Average), but it is reassuring to know that what I'm finding is "as expected".

I'll just leave it in Partial metering mode and not worry about it.

Many thanks.

Roger

I leave mine in Evaluative (with occasional forays into Spot) and use Exposure Compensation based upon the subject and lighting (guesstimate/experience) with confirmation from the Histogram (my main ally!)