Foveon sensors: on field resolution comparison.

The same reference manual lens (Summicron 50mm) was used on 3 different Foveon (SD10, SD14, SD1m) with focus locked to infinity and at its optimum aperture value (f: 5.6).
The following screenshot shows the proportion (at 12.5%) among the different sensor dimensions of the same subject, taken at different times though.
By mistake, the SD1 was used to 800iso instead of 100iso as the other bodies, since I was unable to repeat the shot the colors are not exactly the same and there is more noise, but for the purpose for which it is intended (resolution) it's equally valid.

The first two crops are 300% to be able to read what I consider an "urban optical target" (the railing on the terrace of a building about 200m from my house) that, for the different perspective, is shown with different frequencies of vertical lines. 
The crop of SD1 is instead zoomed at 200% to have approximately the same scale as the previous ones.  I submitted the screenshots in png to avoid jpeg artefacts that could distort the results of the test.

With the SD10 (3.4 surface MPx), the lines on the right half of the railing can be distinguished but are blurred and seem further apart compared to subsequent shots, while the left half (where the frequency of the lines increases) appears as a uniform gray (sensor unable to separate because of too large pixel pitch).

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With the SD14 (4.7 Mpx) things improve a little bit (in proportion to the ratio of the number of pixels), the lower frequencies (right half) are partially solved, but with presence of aliasing (Moiré).

Finally the SD1 shows us the entire right side quite solved and the left part with a residue of aliasing.
The Moiré effect (aliasing) occurs when the resolution of the sensor is less than that of optics, for this reason on the Bayer sensor it's often applied a filter that reduces the lens resolution.
Note that the image's details on the sensor always has the same size (same focal length) for which the increase in resolution is only due to the higher number of pixels which, however, should still be smaller (more in number) to meet the resolution of this lens .

Perspectives.
Since the APSc is virtually half full frame, if Sigma would make a 3x30MP F.F. with the same lens the railing would be the same as you see it now, but if they put 90Mpx on a APSc sensor, the high frequency Moirè (left railing) disappear and you will see everything more clearly. 
But in the latter case the pixels should be with a side of 2.5 microns, so if they do not improve the efficiency of the Foveon technology, the noise will be greater and sensitivity lesser.

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Greetings from Italy.
Italo B.