I have wondered for a while whether my Sigma 120-400mm telephoto lens was sharp or not. I have done tests before but they were inconclusive.
So, time for a scientific approach; what could cause soft photos:- camera shake, poor focus, image stabilisation, technique, quality of lens.
- Camera shake: To eliminate this I put the camera on a decent tripod, locked the mirror up & used the self timer (this was the standard for all test shots).
- Poor Focus: To eliminate this I used both manual & autofocus modes but no real difference showed up.
- Image stabilisation: Off was the best setting whilst mounted on the tripod, when On it showed much more blur.
- Technique: Having done all of the above, I’m tempted to say this is OK although I do need to check settings more before shooting !!!
- Lens Quality: This is where I am feel that the problem lies. I did manage to use the AF micro-adjust on the Canon EOS 7D & using +1 / +2 adjustment seemed to help.