I've had my 24-105mm f/4 L since 2006, and it's been my day-to-day walkaround for most of that time. I always found it difficult to get pin-sharp shots with it, but assumed it was always my technique.
However, I recently decided to check the sharpness of my lenses and perform AFMA calibration on them. What really shocked me is that my girlfriend's EF-S 17-85mm actually appears to be sharper than my 24-105 L!
If anyone here has the 24-105 L, and have done sharpness shots with it, would you mind chipping in? I wonder if this is a naturally soft lens or if mine is out of whack. I know the lens is weakest at 24mm, but mine seems to be pretty terrible!
Standard Lightroom settings, sharpness turned down to 0.
100% crop at 105mm:
100% crop at 24mm: