G9 vs. Z6 @ 2.8 in low light

Started 3 months ago | Questions thread
bobn2 Forum Pro • Posts: 69,811
Re: The theory isn't all that difficult

Anders W wrote:

As I pointed out in a prior post, for example, the data at our disposal suggest that the OP's camera (the G9) has about one stop more dynamic range (and thus correspondingly less shadow noise) than the one he is considering (the Z6) when the two are used to shoot equivalent photos at higher ISOs.

Which data are you talking about? The problem is that DxOMark data isn't available for the G9, so we have to rely on Bill Claff, who doesn't give proper DR measurements. But, Bill's input referred read noise chart (https://www.photonstophotos.net/Charts/RN_e.htm#Nikon%20Z%206_14,Panasonic%20Lumix%20DC-G9_12) shows that the per pixel read noise at high ISOs is better than the G9. So, for instance set to 1600 ISO the G9 is giving 1.866 e- per pixel, whilst the Z6 manages 1.206 at 6400 ISO, so the read noise advantage is to the Nikon. So the Nikon is producing 0.65 times the read noise. This alone suggests that what you say about shadow noise is back to front. it should be the Nikon that produces less shadow noise. (which does seem to be the case, comparing DPR studio shots.

Both very good but the Z6 just slightly better


Of course it has more pixels, so we need to correct for that, giving 0.71, or a stop better read noise. The problem is finding data for the top end of the scale. I haven't found a good way of getting this from Bill's data, but we can do it from raw images, such as the DPR studio scene, which are quite well controlled with respect to exposure. Downloading the raw files from the above and looking at them with Raw digger, selecting the white background from the vertical wedge midscreen the G9 gives an average of 966.8 and a standard deviation of 37.3 in the green channel whilst the Nikon gives 8001.7 and 313 for a similar patch. Thus the SNR for the Panasonic is 25.92 whilst for the Nikon it is 25.56. We can find the photoelectron count per pixel by squaring this. For the Panasonic it is 672 e- and for the Nikon it is 653 e-. Now again we need to correct for pixel size. At 20MP the Nikon figure is 783 e-, suggesting that the QE of the Nikon is 1.16 times or 0.2 stops better (i.e., not worth worrying about) than the Panasonic.

So, for equivalent exposures (same 'total light') and ISO settings the Z6 will produce slightly better DR than the G9, as one might expect given that it has a BSI sensor, larger pixels but lower read noise. However, the difference is tiny, and not worth worrying about either way.

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