It seems I might have antagonised a few MFDB users who have, in desperation, resorted to using the 'ignore' button. So, to make amends for causing so much distress, I thought I might offer a few tips on how to produce an effective DB/35mm comparison, although I have to admit this might not be useful for those who have hit the ignore button because they won't see my post. (Well, I guess that's just too bad!).
In a few months, with the introduction of Sony's 24mp sensor, possibly a 5D upgrade from Canon and possibly a D3 upgrade from Nikon, I get the feeling that many pros will be attempting to offload their old P21, P25, Aptus 22 or ZD back.
To help you get a good price, I'm offering some advice should you ever attempt a comparison between, say a P25 and a Sony A900 or 1Ds3.
(1) The obvious trick is to choose slightly different subjects. For the P25 use an attractive model with full make-up, in an interesting pose against a nice decor, in a professional studio with professionally arranged lighting. Do the best you can. Try to get a nice glint in the eyes. However, for the A900 shot (or 1Ds3, D3 MkII) choose either the same model with no make-up, or another person not nearly as attractive. Change the lighting and try to make the shot look just like an ordinary snapshot that anyone could have taken.
However, I think this trick is too obvious. Most people will not fall for it. Nevertheless, I mention it to help you avoid making this mistake.
(2) We all know that the 4:3 aspect ratio of 645 and that of most DBs is far superior to the elongated travesty of 35mm's 3:2 aspect ratio, so it's quite natural we should crop the 35mm format to the same aspect ratio as the DB, rather than the other way round.
This means that the 24mp A900 becomes effectively a 21.3mp sensor and the 1Ds3 becomes an 18.7mp sensor. The P25 is not really 25mp but 22mp, so this move can easily be justified on the grounds of fairness. It doesn't make a big difference, but any difference at all is welcome if it's in the right direction. After all, we're starting off from what is probably a pretty marginal advantage for the P25 which is due mainly (possibly) to its lack of an AA filter and the choice of lens and lens aperture.
(3) Having matched the FoVs of the short sides of the frames (by using different focal lengths), we now move back just slightly with our A900 in order to give the P25 another slight, but almost insignificant, advantage. No-one is going to complain about a very slight mismatch of FoV. However, if it's in the favour of the P25 it's most welcome. It all adds up to something. The 1Ds3 now effectively becomes, say, a 17.5mp camera
(4) Experienced and knowledgeable photographers all know that it is necessary to use a smaller aperture (bigger F stop number) with the larger format to achieve the same DoF as the smaller format, once Field of View has been matched. Having cropped our A900 to the same aspect ratio as the P25, the F stop multiplier becomes 1.53x. That means that F8 on the A900 is equivalent to F12.24 on the P25. We don't have an F12.24 setting, so it's a choice of F11 or F13. The closest would be F13.
However, let's see if we can get away by completely ignoring this principle. Let's use the same F stop with both cameras, and let's choose a fairly bland F stop like F11 or F13. Not everyone knows that all lenses are equally bad at F11 or F13. If anyone queries us about this choice of F stop, we can attempt a good justification along the lines, 'We wanted to compare the back, not the lenses'. Or, 'We didn't want to disadvantage the P25 with a slower shutter speed'.
(5) Having chosen to use the same F stop with both cameras, always choose parts of the images that are in the plane of focus when comparing 100% crops. This is very important. At apertures where image resolution is affected more by diffraction than anything else, the P25 will have an advantage at the plane of focus because of its greater pixel pitch. However, the parts of the images that are furthest away from the plane of focus are likely to be more similar with regard to detail and resolution in both images.
(6) Raw converters differ in their characteristics, controls, defaults and options. Whatever you do, if you see greater color vibrancy, smoother tonality, or even a 3-D effect in the P25 conversion, do not try to emulate this effect with the A900 conversion. This is most important. If you are tempted to get the A900 image looking as close as possible to the P25 shot, you might risk undoing all the good work you've done so far in the comparison.
(7) Finally, just to indicate that this post is not entirely tongue-in-cheek, one of the greatest strengths of the DB is its great dynamic range at base ISO. Try to drag yourself away from the studio and the lure of creamy skinned models where dynamic range is not a critical issue, put on your boots and get out into the countryside, or preferrably dense rainforest, and shoot a few scenes with dark shadows, with both cameras.
Display 100% crops of the obviously lower shadow noise from the P25 or Leaf 22 and you'll probably have no trouble selling your old DB.
OK? I hope this thread has been helpful and of practical value. Are we now friends again?