Shooting to the right (and overexposing to reduce noise)

You assume that the histogram has some specific layout which it does not. Stops in the histogram are spread out roughly evenly across the horizontal axis of the graph meaning that the histogram is a logarithmic display. That's how you want it to be. Unlike Reichman's implied assertion, one stop does not occupy about 1/5 of the horizontal axis.

Doubling the amount of light does double the output value from the sensor up until the sensor clips.

I never asserted that "expose to the right" didn't result in SNR advantages. I've been practicing it far longer than the LL article has been around and engineers have known this longer than digital cameras have even existed.

Remember that in a 12 bit system, the LSB (least significant bit) represents the lowest stop but that's not the first one. The least significant stop is the last one. Proper exposure sets the most significant stop and the lowest bit is 12 stops down from that. When you look at it in this context you'll understand there is no shadow detail problem unless the exposure is way, way off.

Stops have arbitrary distances on the histogram display and they can vary from image to image. The Kodak SLR actually displays its stop marks, 10 of them anyway, on the histogram directly. They are not evenly spaced across the graph.

You slipped one in on me.

The trouble with this is that I can't just say Reichman's explanation is wrong. It's just misleading and confusing because he freely mixes concepts that he shouldn't.

Histogram displays are really at the whim of the camera or software manufacturer so you can't really say with confidence how they all work. It would be reasonable to say that black is on the far left, white on the far right, and there are some number of evenly spaced divisions between them representing stops of light. Each camera may display these divisions differently. The Kodak, as I said above, has roughly equal divisions, 10 of them, plus an overexposure zone called ERI. You will have to try to understand how your camera works. Your observation that each additional stop moves the image an equal amount to the right is what you'd expect to happen. I'd further expect most cameras to display more like 8 stops in the histogram rather than 10+ like the Kodak.

Still, Reichman's advise is sound in the absence of anything suggesting otherwise. The trouble underwater is that your background will frequently have little red information in it. In such cases you can completely blow out blue or green (or even both) and the histogram won't show it. I wish the camera makers would give a true RGB clipping indicator to help us with that.

Using the biggest possible dynamic range of course has been around before Reichmann and Digital Cameras. I still have to do it underwater with slides. :oops:

Is there no SLR out there with histogram for each channel?

The S2pro will display a histogram for each channel. Too bad they are tiny.

Cheers

James

I believe you have to push buttons each time to get it, too. Isn't that right?

Yes, you have to have the camera set to "Preview with Histogram" which means you have to push "OK" after each shot to save it to media.

After you take the shot, but before you save it to media, it overlays the RGB histogram. Pushing the Func button w/ the Histogram on it will display the R histogram, push it again, you get the G histogram, etc.

It might be good to use it at the start of a dive or a trip to get a good handle on exposure. It's kinda clunky for fast-action shooting though. Don't forget to press OK!

Cheers

James