a fake Topcor 90mm f5.6 (Horseman)?

[landstrykere]

so I got this Horseman 985 last week. Took a 6x9 test roll but only now does it hit me that it is seriously wrong. See, it's a f3,5-f32:



the manual says the 90mm which comes only in "Super" (ie. wide image circle suitable for 4x5) is f5,6-f45:
https://www.cameramanuals.org/prof_pdf/horseman_985.pdf (page 10, printed 7)

I should have jumped when I opened the box and inspected the camera and even more when I tested it with a first roll and was setting the lens at f3.5 and f4 ...but well I guess I was too much distracted by other things since this is my first "technical" camera.
On the resulting images of the first roll I didn't notice differences at f3,5 f4 f5,6 and indeed the iris closes only from f8, there's a bit of a blade visible by the edge at f5.6 but could be just tolerance related to the design being 5 blades:



I was thinking two possibilities:

• may be a repaired lens, shutter was replaced but with the one of a Pro 105mm
• it˝s a fake: a Pro 105mm f3.5-f22, with the front of a Super 90mm.

In order to see if the diameter of the front element is bigger than the hole of the front, I should unscrew the front but I see no notches for a spanner, so I guess it would require more disassembly manipulation than I want to do now.

I measured the length with a caliper and weighted the lens, it is closer to the figures of the Super 90mm, for sure the weight, clearly ~220g like for a Super 90, instead of ~240g for the Pro 105mm (this all in the manual). But...

Since the circle is stated to be 150mm at f22, but the Pro 105mm is 120mm (at f22), I took the 4x5 enlarging back that came with the camera, loaded two sheets of Retropan-320, the only 4x5 film I bought in order to try my hands at 4x5. Indoors, lens set at f8, focusing with a 5x loupe (my Bronica S2 chimney finder) wasn't easy, I better have a 7x or 8x loupe.
Anyway, there's indeed vignetting, but I don't know of course if it is ok with a Super 90mm at f8.
The Pro 105mm has a circle of 120mm, so I guess if this was that lens then there would be a much bigger vignetting than this. Yet there's this insane blur tunnel effect. Maybe the Pro 105mm does in fact cover quite more than 120mm but instead of going just black, with so much optical degradation that only 6x9 is usable?