Trent,
MCWB wrote:I'd have thought that stray light before the shutter is tripped would be the problem, as it affects what the meter thinks is 'correct' exposure?
This depends upon the camera and the metering
modes available and employed.
For instance, what you're saying is absolutely true wrt my FE2: it has no capability of metering during the exposure, and thus the meter parameters are set immediately prior to the shutter being opened.
In the 801 however, the metering sysem is more advanced, and thus the camera meters during exposure in certain metering
modes. Consequently, light value changes during the exposure can have an effect on the actual exposure.
Similarly, the D70 can meter during the exposure, and also during a flash exposure, although during a flash exposure the metering system also, where it can, controls the flash output, setting the shutter and aperture values prior to the making of the exposure and turning off the strobe's output when it deems that enough light has fallen on the subject.
Gary: sure, but if you're relying on the meter to give you an idea of the exposure settings you should be using, it'll still be out?
Highly likely.
And I've yet to see any discussion of reciprocity failure as it affects digital photography. Sure, we have increased noise in cameras line the D70, and we also see colour casting occurring due to the sensorheating up on longer exposures, but is this the same as reciprocity failure?
I honestly don't know.