D3X vs 5D2 - myth and reality

Started Jan 26, 2009 | Discussions thread
OP GaborSch Veteran Member • Posts: 7,203
What to measure

ejmartin wrote:

What you are measuring mixes together a number of different effects.
First of all, by measuring the red patch, you are including
variations in the reflectance of the source (surface roughness) as
well as gradients of the overall illumination in the measurement
patch in the standard deviation

I don't see any problem with that. I don't even see any problem in comparing measurements from different images, and here the very same objects have been used.

This contamination calls
into question why you are reporting 3-4 significant figures in your
measurement results

This is a simple issue: in certain cases I am using calibrated targets, which do yield very reliable results. Anyway, irrelevant.

Second, since the patches being measured are not particularly close
to the black point, there is a significant contribution from photon
shot noise

1. I don't see any "significant" shot noise at -8 EV, and if I could go lower, this would becomne even less relevant,

2. Whatever. This is part of the game, try shooting without shot noise. The other camera is only 1/3 EV off of the shutter time, same aperture.

The 5D2 has substantially higher
read noise for low ISO, at least according to DxO

I have a much lower opinion about that test than you do. This is the essence of my initial post.

On the other hand, if one really
goes close to the black point on their plots, the 5D2 hits SNR=1
(0dB) at about .027%, while the D3x has DNR=5.5dB at this point; the
D3x hits SNR=1 at about .015%. That's about a one stop difference
near black

If one really goes close to the black point, then the Nikopn data becomes invalid in a comparison to the Canon, due to the difference the cameras present the raw data.

I suggest you to linearize the Nikon data first and redo the measurements (and take a close look at the differences between the Nikon and Canon raw data close to black).

I doubt that
the RAW files you are using are sufficient to back out the photon
noise to get at the substantially smaller read noise underneath,
which is what controls the DR near black

I agree with this point. Unfortunately, that's what I have; DxO did not publish their raw files.

When (rather if ) I find someone in my area with a D3X, who is willing to make suitable shots of the Stouffer wedge, I shall present those results.

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