I did a few tests
40D / 5DMK2 - tripod - remote trigger - 1 meter from target - auto exposure - lighting poor on purpose to better see the noise. Shot in RAW, converted to jpeg at max quality with no adjustment whatsoever, ISO 800
- the gain boost is quite visible, maybe a bit less on the 40D, but the auto-exposure chose different parameters.
- the practical impact, at least at pixel peeping level, of the gain boost is more significant than the raw noise number indicate, probably because noisy pixels have a bigger than expected impact on the RAW conversion.
- the DOF decreases as expected (it is very visible on near tangent images of printed text, as posted earlier) at least on the 5D
- the 40D doesn't seem to exploit that DOF increase fully, but that's just a gut feeling, and DOF is bigger anyway.
Interesting data, nicely done. Seems indeed that gain (noise) increases at wider apertures. The change of DOF is clearly visible.
Expected to see slightly more gain (noise) increase of the 40D compared to the 5D as per DxO labs figures / smaller 40D photo sites.
Probably the difference of 0.1EV is neglectable / not visible in this test.
Please note that the DOF of the 40D is smaller because you are shooting both camera's from the same distance.
Calculated DOF for a 85mm lens on both camera's focussed on 1 meter distance is as follows:
f/2.0 1.6cm 1.0cm
f/1.8 1.5cm 0.9cm
f/1.4 1.1cm 0.7cm
f/1.2 1.0cm 0.6cm
Of course these figures are approximate for standard eyesight on printed matter. However close enough for validation of this test I think.
Used the DOF calculator on the Cambridge in Colour site.http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
These distances are very close according your test shots.
So it looks that gain (and noise) is increasing towards wider apertures and still the influence of aperture on DOF remains visible towards f/1.2.