Lens "Sweet Spots"

[HoppyUK]

I have never bothered to test a lenses sharpness across the lens at different aperture before but this thread led me to - damn you stupid thread, damn you.

I only have one lens (get your violins out) and that is a Canon 40 2.8 STM.

In my non scientific shots of a fence I found that my lens seems to be the same in the centre at various apertures but surprisingly the sharpest I got at edges of frame and corners was at 2.8.
The differences were actually small (only noticeable on 100% crops) and I was happy with all of the images at all apertures but good to know that rather than potentially losing at 2.8 I may be gaining.

I realise I am in a lucky position of finding an entry level DSLR with a £140 lens on it as sharp as I need and the camera will never be at fault.

That would be very unusual, thought that particular lens has already got an awesome reputation for sharpness - probably because it's not a very difficult spec to design optically.

This review suggests it peaks around f/5.6 at both centre and edges on full-frame, though it's extremely good right from f/2.8 http://www.photozone.de/canon_eos_ff/752-canon_40_28_ff?start=1

 

[ernesto]

Agree, it would seem unusual. It is very likely to be due to my not very scientific test but even so I have proved to myself that it is safe to use at 2.8 (not that I was actually worried about it anyway) More about having too much time on my hands today than anything else