So, instead trying to scan the 6x7 negatives so that it (almost) fits entirely size of the GFX sensor - i put a slim extension into the VALIO device to further the distance a notch. (Which makes the negative slightly smaller) It still results in to 44 MP scan (instead of 50 MP).

Which is a lot more compared of using the EOS R camera [30 MP], scanning 6x7 negatives resulting into 24-25 MP final scans.

I could still some blur in the very extreme corners - but likely because i now had reduced the aperture from ƒ 16 to ƒ8 on the TTArtisan 100mm ƒ2.8 Macro lens.

The VALOI 120 issue

The extreme corners with the TTArtisan are newer truly sharp-sharp. So, that must be kept in mind. Plus - there there is the pesky flatness issue with the VALOI 120 holders... Funny that nobody ever mentioned this issue in any of the photo forums. How do people scan their negatives ? Giving a rats ass about doing an excellent job ? Maybe nobody cares anymore about good corner sharpness anymore.

Duh - what a cheat these days !

The VALOI 120 holders are designed for UNCUT film stripes - holding them perfectly flat. But NOT when you use cut film stripes (which 99.9% of mediumformat users will and always have done; cutting their negatives in stripes). The negative stripe's ends kind of hang loose without support, so to speak. Film has a natural tendency to bend in the middle. When scanning a negative like that - you will see that the corners are never truly sharp / rarely really sharp.

It can be mistaken that a Macro lens isn't sharp in the corners, I may add.

So; even if I do get a super sharp Macro lens all the way into the extreme corners - the VALOI 120 holders will likely botch the corners still...

So, there is that.

Damn.

The darkroom tripod mounted camera, taking images from above - was still the best quality of all. Here, i used my metal negative holders - and no frikkin' film negative ever bend. It was all flat - like an enlarger negative holder is designed for to do.

FLATNESS is everything.

Diffraction

when scanning images at a higher aperture value like ƒ13 or ƒ16 isn't such a big problem; you can always sharpen up the image just tiny notch extra in order to counteract the diffraction (blurring) effect. At ƒ22 it get's more tricky, though...