Flat-field macro lens for Fuji-X?

I have been alternating between Epson V600 and DSLR (well, actually mirrorless) scanning with my Fuji. The advantage of a camera is speed (especially when scanning 35mm) and resolution, which can be mind-blowing if I'm willing to stitch. I also feel that the camera gives me more bit depth for post-scanning corrections, especially in dealing with dense negatives.

The advantage of the scanner is uniformity and convenience of not having to stitch medium format scans. The uniformity is especially appealing, because my macro lens on the camera is not very good in the corners even at f/8 (probably due to field curvature). This is especially annoying when stitching, because I get these artifacts when stitching software is trying to "marry" two blurry edges. The lens in question is a budget Rokinon 100m Macro.

I hear great things about Fuji's own 90mm Macro but that's a $1,300 lens! I have zero interest in macro photography and that's a lot of money to spend just to improve corners of film scans. I wonder if there's a cheaper older lens I can use with an adapter. I already have an EF-to-X adapter, so getting a used Canon 100mm f/2.8L macro will be much cheaper, for example. I can't find any reference to its field flatness though... Anything else I can consider?

Thanks!

P.S. Another reason I do not want to spend too much is because I have (perhaps unreasonably) high hopes for the new Plustek Pro 120 which was announced almost 2 years ago and still hasn't showed up anywhere.

I've used the Fuji 60mm macro which seems to work well.

By definition, a macro lens is one that gives flat field performance. If it doesn't, it is merely a lens that permits close focus.
As the Fuji X series cameras have smaller sensors, a good quality macro lens designed for film should give good results on the Fuji camera.

Matt, I used to think this way until I bought this Rokinon. I shoot tethered to a computer, and use focus sampler in software. It shows me that sharp corners at different focus distance than the center. Besides, people in old APUG threads and on photo.net used to argue about field flatness of their macros in the past. Even in a recent convo here someone said that enlarger lenses have a flatter field than "most macros". So now I am losing my trust in the "macro" moniker.

Bormental said:

Matt, I used to think this way until I bought this Rokinon. I shoot tethered to a computer, and use focus sampler in software. It shows me that sharp corners at different focus distance than the center. Besides, people in old APUG threads and on photo.net used to argue about field flatness of their macros in the past. Even in a recent convo here someone said that enlarger lenses have a flatter field than "most macros". So now I am losing my trust in the "macro" moniker.

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It doesn't surprise me that a Rokinon lens labelled "macro" is just a close focus lens.
And enlarger lenses do tend to have better flat field performance than some macro lenses, because that is all enlarger lenses do - they image flat fields on to flat surfaces, and usually over a narrow range of relatively high magnifications. Almost no-one uses an enlarger lens to take a photo of, for example, a three dimensional bride and groom standing ten feet away.
A lot of true macro lenses are mediocre at best when photographing subjects at distance. They have, instead, been optimized for other things.
Macro is an oft misused label - see all the 70 - 210 zooms from the 1970s and 1980s with a "macro" setting (actually a close focus setting).
And then there is Nikon, which prefers to call lenses "micro" lenses if they image down near life size. It makes some sense, but it also confuses.

MattKing said:

By definition, a macro lens is one that gives flat field performance. If it doesn't, it is merely a lens that permits close focus.
As the Fuji X series cameras have smaller sensors, a good quality macro lens designed for film should give good results on the Fuji camera.

Click to expand...

Sadly, there may be some lenses that got their "macro" designation from the marketing department, where the definition may not be the same as it would be among the lens designers.

I'll add that I'm functioning well with the Fuji 60 macro. I originally bought it, thinking it would be a very occasional use optic as I'm not into macro activity that much. It turns out that I use it quite often for product shots (for a friend and also some eBay duties for me) and now for the scanning uses. It's a good focal length for portraits, too. It's quite sharp for portrait use (especially with mature folks) but one can manipulate in post around that.