Hi Bart - we've got an Imatest Master license and have shot a slanted edge target as well as a couple of general resolution 'trumpets' :-)
Hi Tim, there you go. I knew you guys had a grip on what you are doing ...
Out of interest, I'm not sure what downsizing the higher resolution result to the lower resolution result is supposed to acheive - it sounds like throwing away information? I can understand that you end up comparing contrast at the highest MTF of the lower resolution result - is this all?
Indeed, comparing 2 MTF curves at 2 different points is one. The outcome is not that easy to predict due to the differences in shape of the curves, especially due to the size difference of the 'sensors'.
I was also thinking about the psychological point of view of a MFDB shooter, who is accustomed to his/her reference, but less so to an upsampled version (only to match a deliberately oversampled filmscan). So by downsampling the filmscan, the familiar reference remains constant, and the unfamiliar rendering can get changed to match the size. A similar reasoning applies to those who are accustomed to large format oversampled scans, they will feel less comfortable with a significantly downsampled version (with risk of enhancing graininess) so the original scan should be the unchanged reference.
As for other suggestions along the line of printing to an identical size and scanning the result, it has it's use, but also adds another variable to the mix which might muddy the waters. Not everybody is equally good at producing large format output, and where e.g. a MFDB might benefit from adding noise, a filmscan might benefit from removing some graininess. It will be very difficult to satisfy all takers. Besides, what is large format for some, is a tad on the small side for others, so what would the output size of choice have to be?
Hence my suggestion for offering both up- and downsampling, and then people can do their own output test, based on their skills and available output modalities from that base material.