Well, this is an interesting thread - thanks to Bart for creating the chart.
Hi Eric,
You're welcome. I agree that apparently the target has helped a bit already to gain more insight in some effects that the total imaging chain can produce. It's due to the target that one can much easier drill down to the cause of things. I know that quite a few people have an allergic reaction to synthetic targets, and they prefer real life subjects to test on (and then there are those that say, get a life - start making pictures instead of shooting targets). But IMHO it is only a useful exercise if one can draw conclusions from the test that help us identify issues, that in turn hopefully can be resolved. It allows us to hone our technique.
The target gets as close to a real life object as possible (all sorts of spatial frequencies in all sorts of directions), but is also abstract enough (luminosity only, repetitive/predictable patterns allows to spot deviations, and it ilustrates loss of contrast with increasing resolution) to allow quantification for comparisons. Even the Raw Converter is challenged as is our sharpening strategy.
I've just printed the chart and spent a few minutes shooting with it and my AFi-ii 12. I'm getting just over 100 pixels blur diameter with the 5.2 micron spacing on the 80mp dalsa sensor but I haven't had a chance to really check my focus and this is with a longish 8 sec exposure in my dark office. Shooting the 130mm chart at about 8 feet with a 90mm lens and it doesn't seem to matter what aperture same result f/4 through f/8.
Something close to 100 pixels seems fine for an MF system, but focus will prove to be more critical than we tend to believe. Digital sensors keep a pretty good MTF/contast all the way to their limiting resolution, but defocus will quickly kill that contrast. Defocus is also a much more efficient Low-pass filter than diffraction. I'd expect little influence from diffraction at f/4 and f/5.6, because the diffraction pattern diameter is smaller than approx. 1.5 x sensel pitch, so the only difference is from residual lens aberrations that get eliminated, if present. From f/5.6 and narrower you'd see a gradual loss of micro detail contrast due to diffraction, but to a certain extent it's restorable with deconvolution sharpening (as long as noise is kept low, a lot can be recovered). It will be interesting to see how well the aliasing is handled between the optical system and the Raw converter.
I think that the target will also serve to improve the quality and predictability of our estimates of DOF, or rather a more realistic assumption of the COC, and enlargeability vs viewing distance of our images.
Cheers,
Bart