Hi Christopher,
I was considering more like mid center performance or rather performance in the sweet spot of the lens. It is not easy to test for corners, as I would need a large test target for that. Yes, I know about brick wall tests.
The lenses I had on mind were:
Sonnar 150/4, Sonnar 180/4, Planar 100/3.5 on the Hasselblad. With 135 I have tested the Minolta 100/2.8 macro and Sony 90/2.8G Macro as far as I recall the 100/2.8 macro has peaked at f/5.6 and the 90/2.8G at f/4.
The question is how much improvement there is in the corners when stopping down. The main aberration may be field curvature and stopping down increases the depth of focus, so that may help.
Not so much MTF data available for MFD cameras, but there is a lot of data for 135 mm lenses from lens rentals:
The example here is the 24-70/2.8 lens at 50 mm, you are right that corners improve when stopping down but the central part looses some sharpness.
I am actually shooting f/8 on 135 and f/11 on MFD, mostly. But, assuming real good lenses I would use a larger aperture for comparisons.
Here is an old aperture comparison I made a few years ago with the Hasselblad/Zeiss lenses I owned at that time, apertures used f/4, f/8 and f/16.
http://echophoto.dnsalias.net/ekr/Articles/Shoots/BernardSamples/CastleShoot/
Best regards
Erik
Sorry Erik, but what lenses are we talking about ? I have shot so many different ones and really don't know a lot which reach their best performance at f4 or f5,6 in the corners. Nearly all lenses show better corner performance at f8 and even f11.
Sure I'm not talking about center or mid center performance. There it is clear that f8 already shows diffraction.