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

Started Feb 23, 2014 | Discussions thread
OP Anders W Forum Pro • Posts: 21,468
Re: In which ways, and why, are smaller sensors more efficient than larger? Part 2

cpw wrote:

Anders W wrote:


While I am glad that you like the idea I introduced in my reply to Joe (Great Bustard) here and presented in greater detail in the OP of the present thread, illustrative examples like the one you provide above can be slightly misleading. First, they have to be done right and this one isn't. The ratio of the D4 sensor area to the S100 sensor area is about 21 whereas the ratio of the ISOs for the SNRs you are comparing (DxO measured ISOs of 1192 and 85, respectively) is only about 14. It follows that the comparison is biased against the smaller sensor. Furthermore, the difference between the S120 and the S100 isn't entirely negligible (more than a dB with the measured ISO kept constant at a point close to 100), which introduces additional bias against the smaller sensor. Second, a systematic analysis across the entire sample of sensors/bodies is of course preferable to a single illustration. You find such an analysis in the OP of the present thread.

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.

The question of QE aside, smaller sensors do better for SNR in this case too (although that may be because they have higher QE). See the results presented in the OP of this thread.

Hi Chris,

See comments below.

Hi Anders,

Ok cool. I only chose S100 because that's all I could find!

Yes, I realize that you chose the S100 because your vantage point involved QE (and thus sensorgen data).

Unfortunately I am user impaired, and can't see your results yet. Is there a way to see it?

Not sure what you mean here. As indicated in some follow-up posts to my OP, the technical appendix that I included ended up as my "signature" by mistake (I used a dashed line to separate it from the rest). Just click on "show signature" to see it. Do you have any problems reading what I said other than that?

Also note that I updated the OP slightly in this post

which also includes the OP itself. So that's the best place to start.

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.

It's an ameliorative procedure all right, but would you say it is easily accomplished (and worth doing) for the ordinary photographer (and outside special applications like astrophotography)?

It takes alot of work and only in its infancy yet for photography, but I could see it incorporated as a button if found to be worth doing.

It would be nice if it could be done automatically somehow but right now it seems like a whole lot of work (particularly since, if I understand things right, it would have to be done separately for each lens, FL, and f-stop, perhaps for each focus distance too if vignetting varies by that).

I have tried it for the raw green CFA in my D40 and can eliminate the PRNU so I know it's possible, but to answer your question about its necessity, I don't really know. It might help for low contrast details and it also eliminates the corner rolloff.

It would be interesting to see how much of a difference it makes, or equivalently, how much of a problem PRNU really is, from a perceptual (as opposed to SNR-measurement) point of view. Personally, as already indicated, I am more worried about shadow than highlight SNR (under the provision that we expose so as not to clip the highlights of course) and my provisional understanding is that PRNU is primarily (though perhaps not exclusively) a highlight concern. But perhaps that's an unwarranted simplification. What's your take on this?

I am of the opinion though, that we pay good money for sensors, and we deserve to have maximum IQ :).


Thanks for all your hard work,

You are welcome. Glad you find it of some interest.

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