I did a test on my 24-105..the other day and again today. I thought I'd post a couple of photos to show you at f4...ITS SHOCKING!!! are they all like this?
I tried the 50mm and its right through.
f4 was at 1/180s
f8 was at 1/45s
So pretty much to get the nice bokeh I want with portraits I can't use the wide open . A bit annoying. The further away the subject it the worse it is. This was taken within the .
These are 100% cropped so you can see.
So looks like f4 isn't worth using on my 24-105mm
These were focused right on the eye and I tried it a few times with the same results.