Dynamic Range -- what it is, what it's good for, and how much you 'need'

Started Oct 17, 2011 | Discussions thread
FrankyM
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Re: Hilarious!
In reply to Great Bustard, Oct 23, 2011

Great Bustard wrote:

FrankyM wrote:

Great Bustard wrote:

FrankyM wrote:

You are assuming that read noise scales with pixel area.

I am not "assuming" -- I am defining "equally efficient sensors" as two sensors with the same QE, same read noise / area, and same saturation limit / area.

Yes, you are defining a situation designed to give you the answer you want.

What is the "answer that I want", and what's my agenda for wanting that answer? That smaller pixels, for equally efficient sensors, always result in greater IQ?

The answer you want is one that demonstrates smaller pixels have higher IQ than larger ones. Your example boils down to a question of read noise, as I said before, so consequently the choice of values determines the outcome. So in effect, you are defining the result.

But if you really want to make a comparison between large and small pixels you should start with a level playing field. Read noise, for a given manufacturing process, simply does not scale with pixel area. Therefore, your definition is comparing apple with oranges.

What is this "level playing field"? Here -- you may find this discussion relevant:

http://forums.dpreview.com/forums/read.asp?forum=1032&message=39651584

No, I don't because I'm not arguing whether larger of smaller pixels have more IQ. I'm saying that if we compare two hypothetical sensors whose only difference is the pixel size and that are manufactured with the same process generation, the read noise of one does not scale to the other by pixel size. If we use different manufacturing process generations then I think it's not a proper comparison.

AFAIK, for a given manufacturing process this is not the case. If you are referring to different manufacturing processes then we are comparing apples and oranges.

It's funny because I just addressed all that in my post above:

http://forums.dpreview.com/forums/read.asp?forum=1022&message=39661473

The reality is far more complex than simple scaling. All I'm saying is that "equally efficient sensors" means the same QE and that per-pixel read noise and saturation limit scale with pixel area throughout the ISO range.

That said, some sensors are pretty close -- e.g. the 5D2 and E5. I mean, they're so close, one might even think that Olympus copied the 5D2 sensor and just scaled it down.

Sorry, I hadn't seen the above post. But it doesn't really answer my question.

What was your question? How read noise varies with pixel size in the real world? Depends on the specific cameras being compared:

http://www.sensorgen.info/

No. If you give me an example where you express read noise/area then I ask what the physics is of read noise varying with pixel area. However, since you now clarify that you were defining a hypothetical sensor whose read noise was exactly 4 times the other sensor of your example, my question is irrelevant.

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