Daaaaaaaamn! Check out the D5200 sensor!

Started Jan 24, 2013 | Discussions thread
Jack Hogan Veteran Member • Posts: 6,481
Re: Aptina?

bobn2 wrote:

I find that the figures at base ISO are often anomalous, for many cameras. Enough so that I exclude them from the QE calculation. I think the reason is that the top end is driven into the sensor's non-linear region, the shoulder of the pixel output transistor's response. The gain calculations are made on the assumption of a generally linear response, when it ceases to be, the gain calculation goes a little awry.

I agree. But what I do not understand in this case (unlike for instance in Canon's) is that we do appear to get a clear shot at a decent-sized 'linear' region of the SNR curve with the appropriate slope (3dB/doubling) around 2% of full scale, far away from saturation and electronic noise. This should be an indication of pure Shot Noise, without the influence of read, PRNU or other types of noise, no?



My elaboration of DxO's D5200 Full SNR graph. Note the linear 'shot noise only' region of the curves

So how do we explain the change in effective QE between camera ISO 100 and 200, knowing that since DxO actually measures Hsat and Ssat doubles, the number of incident photons also actually halves? At camera ISO 200, the effective QE is a loss of 2.66 stops (or 8dBs in the graph), at ISO 100 it is 3.1.

If the photon to electron conversion efficiency in silicon is about 50% (a loss of one stop), and the CFA passbands only let through about 1/3 of the incoming photons (a loss of an additional 1.6 stops), there's 2.6 out of 2.66 stops of effective QE right there. And since neither of these two parameters change when the in-camera ISO is switched to ISO 100, where does the additional 0.5ish stop loss in effective QE, and related additional noise, come from for this setting? We are nowhere near saturation...

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cpw
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