Is my 24-105mm f/4 L unreasonably soft?

[Hannes]

Your curves do look a bit odd. I would have expected them to be more like the 40mm in shape.

My lens on the other hand is sharper at 24mm than 105mm, at 24 it hardly improves on stopping down whereas on the long end it becomes sharp only after stopping down to f8. 50 and 70 are nearly as sharp as 24 but do benefit from stopping down to f5.6 when looking at 100% crops, for normal viewing it doesn't really matter. Probably just down to the good old sample variation.

 

[Mt Spokane Photography]

Something is wrong with the curves, a lens always loses sharpness above f/8.

However, lenses with decentered elements do exhibit strange curves. That's one quick way to spot a lens that needs adjustment.

This are some typical curves. They doesn't go above f/11, but resolution continues to drop off slowly as aperture increases due to diffraction.