Recently I've asked about the difference between two lenses on open apertures: Why do two lenses with the same F-number give different amount of light?
We realized that DSLRs gain the real ISO without letting us to know, when we shooting on open apertures. Matt Grum has linked to DxO article: http://www.dxomark.com/Reviews/F-stop-blues
And here's the chart from this article showing how many stops different cameras lose when we take pictures on f/1.2:
We can see here, for example, that classic Canon 5D has a better performance on open apertures than Canon 5D Mark II.
In that question, we also realized that the camera's ISO gain function doesn't work when we use a manual lens (without electric contacts with camera) or when we use a common lens and turn it around itself (so the camera loses contacts with the lens and doesn't know what aperture set on the lens). If the camera doesn't know anything about the aperture, it doesn't gain ISO at all, even if we really open the aperture (for example, f/1.2 or f/1.4) on our manual lens.
My wish is to verify, is that real that these two cameras has difference performance on open apertures.
Therefore I want to ask somebody who has both classic 5D and 5D Mark II and manual fast lens to make the real test of these two cameras. You need to take two shots using the same lens, shutter speed, aperture (f/1.4, f/1.2 or faster), ISO, focusing distance and distance to the object, but different cameras (5D and 5D Mark II). It also would be great if you has a tripod.
If you don't have fast manual lens, you can use a common fast lens, but you need to turn the lens slightly around itself in order to take away the electric contacts from the place where they should be.