ckatosmith wrote:And I am not sure (lack of knowledge) if that (reflected color cast) can be corrected/avoided, though perhaps using less light, but longer exposures might be something to consider?
If there's a color cast on the moth due to light bouncing off the leaf, then that cast would be very difficult to take out. I won't even say "difficult to
correct" because in that case the camera would be capturing a real effect that would be seen by any sensor. Taking it out would be more like painting a picture based on imagination of what the scene would look like if only the light were not bouncing around as it actually does. The cast might be reduced or avoided by altering the scene and directing the light differently so as to light the moth with more direct light and less reflected light, but that seems far more trouble than it's worth.
Simply changing the amount of light and the length of exposure will not affect color casts very much, or in any predictable way.
In the bad old days of film there was an issue with "reciprocity" that could introduce consistent and noticeable color shifts on very long or very short exposures. In principle something similar could occur with digital because of charge buildup due to leakage instead of photons, but as a matter of practice I've never heard anybody talk about it. If it does occur at all, it would be automatically backed out by custom WB shot at the same shutter speed as the images of subject.
There is still an issue that some types of illumination change color depending on exactly
when you trigger the exposure. I have seen some old-style fluorescent bulbs change color noticeably and cyclically in sync with the AC line power. This is most evident in videos shot to the NTSC spec of 29.97 frames/sec versus 60 Hz AC power to the illumination, especially when the camera is set to use an effective exposure time of 1/125 second or shorter. What happens then is that the exposure window for each frame slowly drifts across the AC power cycle, so that for a while the camera is exposing near the start of every power cycle, then the middle, then the end, then the start again, and so on. As a result, any color shift that is synced to the AC power drifts slowly back and forth with a period of several seconds in the video. The effect had me really confused the first few times I saw it, because I thought it was the auto WB "hunting" and I couldn't understand why it might do that with fluorescent lighting but not with daylight or incandescent. That was the wrong idea. In fact the auto WB was locked in fine, it was the illumination that was hunting!
Flash units also change color a little depending on what power they're run at, plus some units vary in color randomly from one flash to the next, especially when they're run on low power such as 1/64. Those can be annoying, especially for stacking.
These are all really fine points. I mention them only because you seemed interested.
--Rik
