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| p.7 #18 · More Mpix or perfect per-pixel quality? |
I think I followed most of that conceptually, but could you expand a bit on your comment @ deep well depth impacting DR vs. tonal separation. And what do you consider to be optimal/point of constraint/limitation/diminishing return regarding well depth?
I'm just working from simple first-principles without detailed real-sensor technical knowledge; someone like theSuede or kwalsh might have more actual-technology-based information to share. But the basic picture is this: sensor wells are like "buckets" that you can fill up to some maximum number of photons. The bigger the bucket, the more dynamic range you can get between the smallest signal you can distinguish (1 photon in the best case; a handful of photons with sensor readout noise), and the full-bucket count. At the same time, the more full your photon buckets, the easier it is to distinguish fine relative gradations: the 10% difference between 100 photons and 110 photons is hard to distinguish from the sqrt(100)=10 photon shot noise, but the same 10% difference between 400 and 440 photons is twice the sqrt(400)=20 shot noise. If you have gigantic buckets, then you can have plenty of photons in the mid- and shadow-tone regions (so fine gradations are better distinguished from noise), while still being able to count even larger numbers for the highlights.
IMO, if you have "unlimited" light available to work with, then "more is better" for well depth. In situations where you need to crank up the ISO to get the shot, then you're already DR/gradation limited by photon-counting physics (you don't need deeper wells if you can't even fill up a shallower one).
You should be somewhat able to judge for yourself how much even more well depth than what you have would be desirable: when you're shooting at base ISO and setting exposure to keep the brightest parts of the scene just below clipping, how much does the noise and/or lack of shadow detail bother you? With modern sensors, images usually look pretty great, so you may already be well past your own "point of diminishing returns" if you're already happy with the results you're getting. Taking advantage of deeper wells would require exposing at lower equivalent ISO settings (ISO50, 25, 10...) to fill the camera's bigger "photon buckets" with more light (and thus be sensitive to finer tonal gradations, and have more DR between the brightest and darkest signals).
You can simulate the effect of having deeper wells on your camera by overexposing an image by a stop or two, then pulling back the exposure in post. Ignore the badly blown highlights (this is what having real deeper wells would avoid), but the below-clipping mid and shadow tones will be as if shot with a deeper-welled camera (doubling the well depth for each stop overexposure). Compare to a correctly-exposed-as-shot image to see how much you care about the improvements.