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[dcbear78]

From my recent testing of my lenses with Reikan Focal I have yet to find one that has a sweet spot higher than f5.6. Although I have yet to actually test all of my lenses. So I am wondering if the old thought that lenses were best at f8 is still valid? 

 

Here are two of the graphs I have available. The first is the Tamron 24-70mm f2.8 VC lens. I can't remember what focal length I used for this testing now. It's on the report.... Was tested at 70mm.

 

This one is the Tamron 70-200mm f2.8 G2 at 200mm.

 

All lenses will of course be slightly different. But it is interesting to see the actual sharpness of a lens and the point where diffraction kicks in. Not sure if it changes anything, but these were tested on a D810.

 

 

[Merco_61]

A very dense sensor will show diffraction earlier than film or a less dense sensor. The sweet spot, even on 12 MP FX is more often @f/6.3 or f/7.1 than @f/8-11 on modern, quality optics.

 

The subtleties when diffraction starts to show is often masked with film, and the perceived sharpness goes up even after diffraction has set in.

 

I am not at all surprised by your results.