Like i mentioned before, the giant illumination circle of these Mamiya RZ67 lenses (designed for a much larger film negative size) compared to the much smaller Fujifilm GFX sensor - does create stray light pretty often as soon some light shines into the lens. Light which bounces around in the adapter and camera - leading to lower contrast !
There are two ways you can counteract this:
1), if you use your hand (or something that blocks light) very tightly, just outside the visible frame - it leads to better contrast. My hand really where just at the very border, close to become visible in the frame. But i had to get that close in order block the stray light in an effective, visible way.
2) you can of course change contrast, in various ways in Adobe RAW-plug locally or overall. Or combining both techniques in order to achieve great looking images.
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1 left: Visible Stray light, creating lower contrast . . . . 2 right: Hand right above the lens; more contrast
Mamiya Sekor Z 100-200 mm ƒ5.2 ZOOM
Now this one, was surprizingly "bad" in terms of chromatic abberations. (takes more time to correct manually) Of all lenses this far, showing most chromatic abberations. (albeit not as bad as the Pentax 67 SMC 300/4 (non ED) lens.
• Mamiya Sekor Z 50mm ƒ4.5
• 65mm ƒ4
• 90mm ƒ3.5
• 250mm ƒ 4.5
Are all very well-behaved with very little chromatic abberation, when used wide open.
• Sekor SHIFT Z 75mm ƒ4.5 has slightly more
• as does 150mm ƒ3.5, as well the 360mm ƒ6
• but the 110mm ƒ2.8 slightly less.
Overall facit: less chromatic abberation than most Pentax 6x7 lenses, when used at wide open apertures.
• Mamiya APO Sekor Z 210/4.5
showed no chromatic abberation what so ever. Very sharp wide open and even more so, even when stopped down. A wonderful lens ! Seems however having a longer minimum focus distance. The 45mm tube doesn't really change the min focus distance as much as i thought.
• Stopped down - all Mamiya RZ67 lenses are very good.
• All of the lenses exhibit various levels of flare (diffuse stray light, lowering contrast) when broad light is shining into the lenses.
• The Mamiya Sekor Z 100-200mm ƒ5.2 zoom showed chromatic abberation even when stopped down. It is the "worst" lens. Well, I still have not checked all of them. Perhaps the Fish-eye Sekor Z is a candidate of strong chromatic abberations, too ?
Mamiya Sekor Z 360 mm ƒ 6
This turned out far too wobbly for my taste - unsure to determine the true optical performance of this telephoto lens. It has relatively little chromatic aberrations, especially stopped down. But the whole adapter setup of mine was simply ... far too unstable.
It seems to be relatively sharp when stopped down. A little bit of Topaz artificial sharpening did give good results. But it isn't a mainstream lens exactly. Yet it should be noted that this lens is highly affordable for little money.
Anyway - it is lost on a stupid adapter, of course. (Next time i try it at infinity outdoors, short exposure times, and without 45mm extension tube).
The Pentax 67 SMC M* 300/4 ED IF in comparison is the better lens; way easier to handle - and has its own movable tripod foot which makes it flexible as well sturdy. On top, it has a fantastic minimum focus distance of just 2 meter. Clearly my favorite in the 300-400 mm class of mediumformat lenses.
In the images below
The first was taken at aperture ƒ6 (wide open) and the second at ƒ16
I was standing 3+ meter away, despite having the 45mm No 1 extrension tube employed. a lens far too long and heavy for the fotodiox adapter (with support fix) and 8 seconds exposure.
I applied some AI sharpening to both of them. | 
