Light meter adjustment for a manual focusing screen

Question

Katz Eye has replacement focusing screens for semipro Canon cameras, but they do affect the light meter in some situations. I am rather fond of using my spot meter, but am annoyed by the effects of not being able to properly gauge my focus with wide apertures. Are there any suggestions for coping with this?

I think it would be the best outcome if there were some way to adjust the light meter in the camera, but I don't believe the camera software supports mapping the light meter readings (some situations have no change, some are positive, some negative).

Answer 1

I don't think it is possible to do this. The effect of the matte screen on the light by aperture is non-linear. Canon gets around this by having pre-programmed their cameras with the effect of the different Canon mattes at different apertures, so the camera can adjust accordingly... no such easy fix for the third party screens. On the upside - you have the ultimate metering tool available in the form of the histogram, even if it is after the fact. If you shoot in manual mode, in reasonably constant lighting, this is the final word on the matter and metering is not actually all that necessary. People lived quite well without in-camera light meters for better than a century, after all - the histogram is vast improvement upon this.

Answer 2

I'm guessing that Canon's spot meter can be set to any of the focus points. That's the situation with Nikon, anyway.

If you know (or can measure with the help of the histogram) the effect the screen has on a specific spot metering/focusing point, you can set a exposure compensation when using spot metering and only use that metering point.