On the comparison of f/64 8x10" and MFD f/11 I made;
If we assume infinite resolution on the sensor and infinite resolving power of the lens, ie diffraction is the only factor limiting resolution, there's a zero sum game between formats in terms of resolving power and DoF.
If you make the format larger, you need a longer focal length to match field of view (FoV) and then you need a smaller aperture to match DoF, and then you get punished more by diffraction so you end up not gaining any resolving power despite the larger format.
If you go the opposite direction from larger to smaller you need a shorter focal length to match field of view, but to resolve as much as the larger format you need to reduce diffraction and thus open up the aperture, ending up on a zero-sum.
Conveniently enough, the you can use the crop factor both on focal length and f-number to find the corresponding match when going between formats.
8x10" diagonal is about 320mm, 48x36mm MFD is about 60mm, that's a 320/60=5.33 crop factor. 64/5.33=12, that is f/12. For full-frame 645 it becomes ~f/13, so f/11 was a bit of exaggeration on my part, you need to get down to 44x33mm for that...
That is if you want to resolve as much as 8x10" at f/64, you can't shoot at a smaller aperture than f/11 with your 44x33mm sensor (and you need like 600 megapixels on that sensor of course...). The point was showing an example that f/64 is not that deep DoF as it might sound in modern ears.
If we assume infinite resolution on the sensor and infinite resolving power of the lens, ie diffraction is the only factor limiting resolution, there's a zero sum game between formats in terms of resolving power and DoF.
If you make the format larger, you need a longer focal length to match field of view (FoV) and then you need a smaller aperture to match DoF, and then you get punished more by diffraction so you end up not gaining any resolving power despite the larger format.
If you go the opposite direction from larger to smaller you need a shorter focal length to match field of view, but to resolve as much as the larger format you need to reduce diffraction and thus open up the aperture, ending up on a zero-sum.
Conveniently enough, the you can use the crop factor both on focal length and f-number to find the corresponding match when going between formats.
8x10" diagonal is about 320mm, 48x36mm MFD is about 60mm, that's a 320/60=5.33 crop factor. 64/5.33=12, that is f/12. For full-frame 645 it becomes ~f/13, so f/11 was a bit of exaggeration on my part, you need to get down to 44x33mm for that...
That is if you want to resolve as much as 8x10" at f/64, you can't shoot at a smaller aperture than f/11 with your 44x33mm sensor (and you need like 600 megapixels on that sensor of course...). The point was showing an example that f/64 is not that deep DoF as it might sound in modern ears.