In which ways, and why, are smaller sensors more efficient than larger? Part 2

Started 6 months ago | Discussions thread
Anders W
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Re: In which ways, and why, are smaller sensors more efficient than larger? Part 2
In reply to Anders W, 6 months ago

This is a response to Joe's (Great Bustard's) post here in a recently expired thread on the same topic as the present one.

Great Bustard wrote:

Anders W wrote:

You aren't off at all. What I wanted to say in general (apart from the comparison between the D4 and the E-M5 already discussed above) is the following:

The difference figures in the last column indicate that for both cameras, and especially the D4, the difference in SNR as we half the exposure (going to the next higher ISO) is significantly less than the 3 dB figure we would expect under the premise I mentioned (constant QE, no fixed pattern noise, trifling impact of read noise), especially in the lower part of the ISO range. Since we know read noise to have a trifling impact in that range, it follows that either QE isn't constant across ISOs and/or there is significant fixed pattern noise. This may be at least part of the explanation why my results for normed max SNR differ from Bob's QE figures.

For the purpose of measuring sensor efficiency, I think the implication is that we should move away from the simplified view provided by a focus on QE (as a constant for each sensor) and read noise. Instead I would suggest, that we use four measures to capture that efficiency. The three measures I have already constructed plus a fourth focusing on "normed max SNR" at higher ISOs. As I hope/think you agree, the two DR measures are good indicators of efficiency with regard to shadow rendering at low and high ISO and the two SNR measures are good indicators of highlight rendering at low and high ISO. So we cover variations in efficiency across the ISO range as well as between shadow and highlight rendering. What do you think?

I think we need to discuss PRNU, as Chris discussed below. For example, consider the EM5 at ISO 107 (42.2 dB) and ISO 394 (37.4 db). These exposures are 1.88 stops apart, which should correspond to a noise differential of 5.66 dB vs the measured 4.8 dB, where this discrepancy is due to PRNU.

In other words, PRNU prevents not only the one stop noise advantage of FF over mFT for the same exposure, but the one stop noise advantage of ISO 100 over ISO 400 for exposures two stops apart.

I have now addressed that problem in a systematic fashion in the manner I already outlined. See the OP of this thread.

As Chris states downthread:

http://www.dpreview.com/forums/post/53174252

"What the data really says is: When comparing sensors at equivalent operating points (higher ISO for the FF and near base ISO for the smaller sensor as I wrote above), both large and small sensors with similar QEs operate with similar SNRs. When we try to operate the large sensored camera at its lower ISO, an operating point that the small sensored camera can't operate at, then it's achievable SNR, while being larger than at high ISO, is not as high as it could be due to PRNU. This last point, of PRNU limitations, can be ameorilated by use of flat-fielding, which would allow the sensor to operate at its shot noise limit."

See my reply to Chris here.

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