I take it that the MTFs for diffraction (at a fixed aperture), pixel aperture and the AA filter are all constant? Also that diffraction and pixel aperture MTFs can be quite accurately estimated?
Yes, and the more you narrow the wavelength of the light the better, that's why I like to work with the green CFA raw channel only, which for some Nikon cameras has 1/2 power bandwidth of around 540nm +/-50ish.
That leaves the unknowns, which are the lens blur and AA filter. So, if you take two shots, the only difference being a slight change in the lens blur ... could you not then work out the AA from that? Notice that I say you, because I certainly could not! And no doubt it's not possible to do or you would be doing it already.
Lens blur is the hardest of the simple components to model because it depends on so many variables (if we concentrate on the center only of well corrected lenses at least SA, CAs and defocus): it changes model significantly and non-linearly with even small incremental variations. So far I have concentrated on modeling well corrected prime lenses with small amounts of defocus in the center of the FOV. By small I mean less than half a wavelength of optical path difference (Lord Rayghley's criterion for in-focus was 1/4 lambda OPD). It has the finickiest theory and it is the plug in my overall model: diffraction, pixel aperture and AA are set according to their physical properties and camera settings. Solver than varies OPD to get the best fit to measured data. There is always a residual value because no lens is ever perfect. I have never seen it at less than 0.215 lambda, which corresponds to a lens blur diameter of about 5.3um (on a 2.4um pitched RX100vIII).
I had a quick look at MTF Mapper and it seems very good. If you could give me your command arguments I could use it to check my image before sending it to you.
I don't have Imatest so perhaps you can set it up to do the same thing, and trust me it would be much easier. MTF Mapper is excellent because it allows one to work directly on the green channel raw data, without introducing demosaicing blur into the mix. The author, Frans van den Bergh is a very smart and helpful guy whose blog got me going on this frequency domain trip. On the other hand it is an open source command line program which is not as user friendly as commercial products. This is the way I use it, you may not want to once you realize what's involved
1) First create a TIFF of the raw data with dcraw -D -4 -T filename.cr2;
2) Open filename.tiff in a good editor and save a 400x200 pixel crop (horizontal edge, 200x400 vertical) of the central edge you'd like to analyze in a file called, say, h.tif making sure the top left most pixel of h.tif corresponds to a Red pixel in the original raw data (use RawDigger for that)
3) run the command line "mtf_mapper h.tif g:\ -arbef --bayer green -t x", assuming that you are working in directory g:\ and x is the threshold (your last two images worked with x=0.5)
4) MTF Mapper produces a number of text files and Annotate.png: open mtf_sfr.txt in Excel using the data import function. There should be four lines with 65 values each. The first value of each line is the angle of the edge (ideally it should be somewhere between 5-10 degrees). The remaining 64 values are the MTF curve in 1/64th cycles/pixel increments, starting with 0 cy/px which clearly has an MTF value of 1. Choose the line that corresponds to the edge (see the Annotate.PNG file) and plot it.
Voila', that's the MTF curve of just the two green raw channels. Alternatively send me the file (one at a time please) and I'll do it for you - I've got batch files for most of this but they reflect how I work, call other programs and they are not easy to explain or set up if starting from scratch.