D600 High ISO in DX

Started Nov 23, 2012 | Questions thread
bobn2
bobn2 Forum Pro • Posts: 62,004
Re: Clarkvision.com analysis
1

Leo360 wrote:

bobn2 wrote:

Leo360 wrote:

bobn2 wrote:

Leo360 wrote:

Leo360 wrote:

So far from what I saw on Bill Claff's charts is that D600(DX mode) dynamic range outperforms D7000 at all ISOs. I have no reason to think that with D5200 it will be any different.

Leo

For those interested in the subject of sensor performance with all the gory details, please, read the sensor section at the clarkvision.com. Highly recommended read!

Only highly recommended if you want to end up getting all kinds of stuff wrong. Which seems to be what you have done. Particularly, the section on the effects pixel size is extremely confused.

And how exactly it is confused?

Where to start? I've done this so many times. If I was sensible I would just keep a bookmark, but I'm not that organised. OK, going from the top:

Dynamic range is defined in this document and elsewhere on this site as:

  • Dynamic Range = Full Well Capacity (electrons) / Read Noise (electrons)

Moreover, Roger predicts that 5um is the optimum pixel pitch for any CMOS sensor. Bob, what is your take on it?

That is one of his most amusing results. He predicts that 5μm is the optimum pitch simply because he decided that was what he would do. Here is the definition of FSAIQ:

FSAIQ = StoN18 * MPix / 20.0 = sqrt(0.18*Full well electrons) * Mpix / 20.0,

where StoN18 is the signal-to-noise delivered by the sensor on an 18% gray target, assuming a 100% reflective target just saturates the sensor, and Mpix is the number of megapixels. StoN18 is computed from pixel performance before Bayer de-mosaicing: indicative of the true performance of each pixel.


So, FSAIQ is given by pixel size times QE (Full well electrons) times pixel count, which is sensor area times QE. Then Roger says proudly

The model closely predicts performance for all modern cameras

Not surprising, since all the model says is that the bigger the area and the higher the QE the better.

However, that result doesn't suit Roger, who goes on to fudge the FSAIQ curves by including 'diffraction'. The FSAIQ as above has no element for 'diffraction', but Roger puts that in the curve anyway. He does that by limiting the Mpix figure according to a 'diffraction limit' (another phenomenon that does not exist) chosen at arbitrary f-numbers so as to give the 5 micron peak. It is a completely bogus and false result imposed simply because it was the result he believed in and he fudged the figures to produce it. Utter nonsense.

The overall pint is this,Roger (and you) is obsessed with comparing things at the pixel sampling frequency, which means making comparisons over different bandwidths. That produces nonsense results, particularly nonsense if what you are interested in is, if you take like photos from the two cameras being compared, which looks better.

I cannot speak for Roger but I am NOT comparing across pixel sampling frequencies.

Yes you are, you might not think so, but by seeking to compare DR or SNT 'at the pixel level' that is exactly what you are doing.Pixel size determines sampling frequency which determines recorded bandwidth but not observed bandwidth.

On the contrary, I am re-sampling the higher freq. image (think down-sampling) to a common sampling rate and then comparing at the same reference frequency. And down-sampling (when performed properly) tends to improve SNR.

Down sampling is unnecessary, all that is necessary is to observe the images the same size. For instance an A3 print is 18MP on a Canon 300 ppi printer. On an Epson 360 ppi printer it is 25MP. So if I took, for instance, a 1DX image I could print at A3 on a Canon without significantly resampling. I could do the same with a D600 on an Epson. If I compared the prints the noise would be substantially the same, without any resampling having happened, simply because it is the viewing size and the acuity of the viewers eye that determines the viewing bandwidth, so long as the output device pixels are below the limit of acuity.

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Bob

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