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 p.5 #15 · Utility of dynamic range beyond a certain point | |
ilkka_nissila wrote:
That would be an exposure issue and the reduced shadow noise (in the A7RVI compared, e.g., with the A1II), which is what the extra DR is all about, is not likely to help much with that. You can choose to give the subject less exposure and by doing this you can avoid the highlight clipping but also whenever you give yourself more room in the highlights for brighter spots to be correctly imaged, you increase noise in the darker parts of the image due to increased photon shot noise. The differences in DR are likely to be visible in the darkest shadows at low ISO and it's not clear they would make a difference in most practical use cases. The differences in DR (between A7RVI and A1II) are present in the ISO 100-500 range while photonstophotos.net shows practically identical PDR at ISO 640 and higher; how often would bird photographs be made at max ISO 500? It's certainly possible but I think most bird photography happens at medium to high ISO these days.
I think it's brilliant that such developments still occur in camera sensors and think people who shoot at low ISO will find uses for the reduced shadow noise. However, if you actually take a landscape and bracket the exposures (assuming there is little movement in the scene) and merge the exposures carefully, you will get a much larger reduction of noise and improvement of the final image, but of course, this requires a lot of skill and a good eye when doing the editing. For shots where there is movement in the scene, single-exposure DR can matter, but because of the ever-present photon shot noise, the differences between camera generations might not be as important as they once were in this area of technical image quality improvement. At high ISO, different technical implementations might be more effective in optimizing the DR. Certainly if shooting flying birds at ISO 25600 before the sunrise, any image quality improvement that can be had is welcome, as the starting point is not very good, but may still show interesting behavior.
Examples of where base ISO DR might matter (and when bracketing is still a useful tool) is landscapes that include the setting or rising sun in the image. People love sunsets and sunrises and depending on the foreground, there can be a huge lighting contrast between some rocks and the brightest part of the sun. Whether this type of photography is any particular photographer's cup of tea is another matter, of course. ...Show more →
There seems to be something contradictory in "You can choose to give the subject less exposure and by doing this ... you increase noise in the darker parts of the image due to increased photon shot noise."
Statistically, the shot noise increases as the square root of the signal. E.g., for a signal of 100 electrons, the shot noise is 10, and for a signal of 10000, the shot noise is 100.
The absolute value of the shot noise is not important (except in the highlights), because the (engineering or photographic) signal-to-noise ratio increases with more light despite the concomitant increase in the shot noise. E.g., quadrupling the amount of light captured by a sensor gives a two-fold increase in the signal-to-noise ratio.
I agree with "The differences in DR are likely to be visible in the darkest shadows at low ISO and it's not clear they would make a difference in most practical use cases" with reference to the A7RVI. One practical question about the A7RVI is in what tonal region the noise (that must be the shot & read noise in the signal prior to the analogue-to-digital conversion) is reduced?
If we divide the region below midtones into (a) Light shadows, (b) Deep shadows, (c) Extreme shadows, I wonder which one(s) should have have reduced noise due to the dual gain? You use the expression "the darkest shadows" that probably corresponds to my "Extreme shadows", however, I don't have the knowledge of how dual gain is implemented in the A7RVI to make any concrete statement.
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