testing a lens for sharpness

[tdodd]

I don't disagree tim, but it should be in moderation as the point of ensuring you've got a sharp copy is to use the kit to take pictures - we don't want to wind up like those motorheads who spend years and thousands of pounds tuning, tweaking, and modifying their cars, but never actually get out and drive them for fear of the chromy bits getting dirty

It's not an ongoing task though. You do it once, and then unless something changes radically you leave well alone. I think it's a pretty safe bet that when a lens needs +11 I'm probably going to be better off leaving at at +11 then resetting it back to zero.

A small point to add though, because I've actually confused sharpness with focus in my earlier reply, and obviously they are not the same thing. You can have a sharp lens that may look soft because it is misfocused. Misfocus may be an easy DIY fix, with a suitable body, but a soft lens is a soft lens, period, and needs to be sent back to be replaced or fixed. But if all you do is go out and shoot,and find you have soft results, how will you know the cause without closer investigation? It could be shutter speed too slow. It could be aperture too small. It could be high ISO and heavy handed NR. It could be a crappy filter on the lens. It could be poor focus through user error, or through equipment malfunction, or it might just be a soft lens.

So IF you have poor results it is testing time. IMHO the easiest way is to use a tripod and in good, bright lighting use Live View and Live AF to focus on a sharp, contrasty, flat target set parallel with the sensor. Zoom in to 10X magnification and judge whether or not the image is sharp. If it is then your lens IQ is OK and the problem with softness must lie elsewhere. Next step is to use Quick AF and see if the result deteriorates. If it does then you have an AF calibration problem. If it's just as good as before then you have a sharp lens that is well calibrated. Your problem must lie elsewhere - technique or settings.