I’ve just read your other thread ‘Lens vignetting and flat field correction’. I hadn’t read it before but weirdly this afternoon I was experimenting with my own Fuji X-T2 with a 55mm. Micro-Nikkor f2.8 and a 14mm PK-12 extension tube, and a Fuji to Nikon adapter of course. I wanted to see if there was an optimum distance between the Cinestill CS-Lite source and the negative/slide as I’m going to make a permanent enclosure to use for 35mm and 120 stitching. For testing I put a blank colour negative frame in a slide mount and tried it at 15mm, 30mm & 45mm. They were all very even, a tiny amount of vignetting which I will attend to with a positive +1 correction if I’m doing negatives, not noticeable with positives at all, I don’t in any case have flat field correction on my Lightroom 6.14 though it was at one time available as a download plugin.
So I didn’t get any of this effect of darkened edges (before inversion), I do rather suspect the Skier box. I’m going to have my CS-Lite 30mm below the negative though 15mm would have been fine I think and 45mm just unnecessary. I wouldn’t want it closer than 15mm though as I want it to be well out of focus, particularly for 120.