What I learned from Gollywop -- and what I wonder

Started Mar 26, 2013 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: What I learned from Gollywop -- and what I wonder

texinwien wrote:

LincolnB wrote:

bowportes wrote:

Something that's not as clear to me though. If ISO is at base (160 for most Pannys and 200 for Olympus), the lens is at maximum aperture, and shutter-speed can't be set slower, but the histogram still sits right in the middle -- not overexposed at all -- if I understand correctly, I might get some improvement in image quality by raising the ISO to 400 or 800 in order to overexpose the image, as long as I'm careful not to overexpose to the point where I'm clipping highlights. I'd like confirmation that this is correct.

You might get less highlight clipping and less shadow noise but you'll get more sensor noise overall. There is a trade-off.

I believe that is incorrect. Assuming exposure stays the same (same luminance, aperture and shutter speed), going from a lower ISO with higher read noise to a higher ISO with lower read noise (say, from ISO 200 to ISO 400 on the E-M5) will net you less noise.

You are right in this case tex.

It will, however, also net you less dynamic range, tonal range and color sensitivity. That's where the tradeoff comes into play with this strategy. You have to decide whether the drop in read noise is worth the tradeoff in the loss of dynamic range, tonal range and color sensitivity that comes along with it (when bumping ISO from 200 to 400 on the E-M5 and keeping exposure the same, as an example).

But you are wrong here. Going from ISO 200 to 400 on the E-M5 under these circumstances (where, importantly, you cannot increase exposure any further and you are still at least one EV short of the clipping point if you stay at base ISO) will bring you only advantages (significantly lower read noise, and thus significantly lower shadow noise), no disadvantages.

What you must keep in mind here is that the DxO figures for dynamic range, tonal range, and color sensitivity are for a sensor exposed up to the clipping point. If you are below that point, the figures are correspondingly lower. What you must also keep in mind is that things like dynamic range, tonal range, and color response are not distinct from noise. They are just different ways to index noise. We need multiple measures of noise because, as with pretty much any attempt to reduce a complex reality into a single number, none of them tells us everything we might want to know.

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