B&W Filter Conversion Question

[Steve M.]

I've generally found B&W filter conversion factors confusing. On one camera of mine I don't have to do anything, the camera's meter takes care of it accurately. On another camera (both are TTL) I have to manually correct because it's meter doesn't "see" the right correction factor. Plus, shooting different colored objects will call for different corrections even on the same filter.

My usual filter for B&W is the usual yellow filter. It bumps the contrast up a bit, and darkens skies (if there's blue in the sky) a fair amount. But red filters sometimes throw me. I have a Kenko red filter and it's marked 2 R1, which to me would indicate give it 2 stops correction. Yet a red filter usually calls for 3 stops. Other than doing a test and bracketing, any ideas?

 

[michaelwj]

I've generally found B&W filter conversion factors confusing. On one camera of mine I don't have to do anything, the camera's meter takes care of it accurately. On another camera (both are TTL) I have to manually correct because it's meter doesn't "see" the right correction factor.

Sounds like the meter is not sensitive equally across the spectrum

Plus, shooting different colored objects will call for different corrections even on the same filter.

Obviously, the filter is changing the relative brightness of the colours.

My usual filter for B&W is the usual yellow filter. It bumps the contrast up a bit, and darkens skies (if there's blue in the sky) a fair amount. But red filters sometimes throw me. I have a Kenko red filter and it's marked 2 R1, which to me would indicate give it 2 stops correction. Yet a red filter usually calls for 3 stops. Other than doing a test and bracketing, any ideas?

Try metering off something neutral, like concrete or something black. Remember that grass is actually quite yellow.

Michael