Tamron SP 500/8 Adaptall-2 shows "f/4" on my Nikon-AI mount!

Hello friends,

I'm a bit confused - my newly acquired catadioptric 500\8 Tamron SP lens (the latest sort of it, 55BB) says "I'm a f\4 lens" in direct aperture readout window when the Nikon-AI Adaptall-2 mount is put on it. Other Tamrons like 44A lens say the truth about their aperture Is it normal? The cutout designed for one of the mount's handles is placed on this lens in a spot that doesn't allow for much doubts. How would the whole contraption work with Nikon FA in, say, aperture priority mode? Am I alone with it, or it's a known thing? Neither the lens nor the mount were modified in any way, of course.

Regards from Moscow,
Zhenya

As far as I recall Zhenya , you need to check this out because it's about twenty years since I sold them, but with the FA I think you need the AIs mount, after mounting the lens set the camera to f8 on aperture priority.