Originally posted by tengier The issue starts from Aperture 9.5 (half stop on a ring between A8 and A11). From that point up to A22, I can move the ring slightly within the same "click" and can see 2 different Aperture values.
To me it looks like the cogs on the other half of the ring are slightly (?) worn out, they don't keep their assigned values. My other lenses are FA and I didn't notice anything like that on them.
And finally, when the depth of field preview button is depressed and I move the ring slightly (without jumping to the next half stop), I do not see any difference.
The fact that this only happens from f/9.5-f/22 indicates there is something wrong. However, if there is no change observed with the depth of field preview, then it's only electronic misinformation in the viewfinder that wouldn't affect your exposures if you're shooting in metered manual exposure mode. However that is still confusing if you're relying on the viewfinder info for light meter readings and can certainly affect the exposures if shooting in aperture priority mode. The only way to know that is with a test roll.
In general, I only use my FA lenses on my 645N and A lenses on the 645, but again, just the fact it only happens from f/9.5-f/22 tells me the problem is isolated to that lens. I doubt it would be a cheap or simple fix; probably return to sender