Strange low contrast in middle of negative Fuji gsw690ii

Have you tried taking the same photo with a fully wide open and a fully closed down aperture?

If it’s small & distinct wide open and becomes larger stopped down it might be something wrong with the very centre of the outside element of the lens.

Have you cleaned it yet with a drop of lens cleaning fluid on lens cleaning tissue? That might clear it up, or, show there is something going on, such as an area where the lens coating has been somehow removed or reduced?

skahde said:

A bright muddy sky is in my experience about the worst to expose the flaw of internal reflections inside a lense and the result looks more or less like above. I had the same thing with a Tamron 2.5/90 mm. Reason was a reflection from the last element form damaged coating. A summicron 35 v4 did the same when it had some smear on the last element (not to self not to throw chocolate-wrapping into your bag). Have a second look for haziness when shining a light into the lens from the rear with a dark background but with the light outside of your view. Then take the light shine and look into the camera from the rear: Anything reflective you can find?

Click to expand...

I second this opinion. I had a similar problem with a Hassy 80mm F/2.8 Planar mounted via adapter to a Canon digital camera. Turns out the adapter was not properly flocked inside and the internal reflections resulted in images which exhibited the same kind of problem you are experiencing. It was not on every exposure, and was most prominent in one patch of the image -usually the center, and most notable in studio portraits shot against a solid background. Perhaps the internal surfaces of your lens or camera, the diaphragm blades in the interlens shutter, or even your lens hood has a shiny spot that is causing internal reflections when the light hits it just right.