Are bigger pixels less noisy?

Started 4 months ago | Discussions thread
57even Forum Pro • Posts: 15,487
Re: Are bigger pixels less noisy?

bobn2 wrote:

57even wrote:

bobn2 wrote:

57even wrote:

I don't think that - at moderately high ISO - pixel size makes a significant difference. Or rather, the design of the pixel makes a bigger difference than the size. Read noise is quite unpredictable and doesn't correlate all that well with sensor size.

I think the problem with the approach that you are arguing against is the desire to find absolute rules such as 'bigger pixels means less noise'.

Where was I doing that?

The actuality of designing sensors is one of trading off many different design parameters, and it is not a given that one design parameter on its own only gives benefits. Let's take pixel size, for instance. A big pixel might improve the proportion of incident light captured due to a higher fill factor. But then it will need a higher saturation capacity if it is to operate at the same exposure. That means a lower conversion gain which will increase read noise. Then the potential gradients in a large pixel will be shallower, so it might be more difficult to transfer the charge to the read gate, so the conversion efficiency might be lower than a small pixel. The only way to make generalised statements is to look for trends in performance data, and those don't show significantly better noise performance for bigger pixels.

Where did I say it did?

Sorry, a misunderstanding here. I wasn't disputing anything you said, I was backing up your position. I thought I'd made that clear when I said 'the problem with the approach that you are arguing with',

That could be taken either way when you think about it...

rather than 'the problem with your argument'. Obviously not clear enough. Sorry about that.

No problem. What you said about conversion gain is also true, but set that against larger source followers having less 1/f noise, and DCG which nullifies the gain issue.

However, there are interesting differences in some cases between dedicated low res sports cameras and their high-res landscape siblings, where the former have superior DR at high ISO (sometimes significant) and worse DR at low ISO (also significant).

A7S vs A7R4

https://www.dxomark.com/Cameras/Compare/Side-by-side/Sony-A7S-versus-Sony-A7R-IV___949_1326

D3s vs D3x

https://www.dxomark.com/Cameras/Compare/Side-by-side/Nikon-D3X-versus-Nikon-D3s___485_628

However, the D3 was no better at high ISO than the D3x, so this seems to be more to do with electronics than pixel pitch.

The low ISO issue seems to relate to gain and downstream noise - the high ISO difference seems to imply lower upstream noise (as a proportion of signal when normalised).

Or some massaging of the data in camera.

BTW, spoke to a friend who used to work for Pentax. He reckons they stuck with SOS to match their light meters at the same ISO (which they apparently do).

Can't say why Olympus or Fuji do it, but it's notable that they both use a much higher IE than the equivalent ISO speed. (ISO 200 vs 100 for instance). This should also align pretty well with a light meter with a K value of 14 (eg a Pentax one).

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