theextremist04 wrote in post #11222942
Go out and take pictures. Come back, look at them, you'll know if something isn't working because they won't be in focus. It's pretty easy.
philwillmedia wrote in post #11222985Yep, pretty much sums it up.
Also don't pixel peep.
Pixel peeping will drive you nuts - you'll end up tearing your hair out.
You'll find "problems" that aren't there and the more you look for something wrong, the more you'll find.
The reality is that 99.9% of the time, there is actually nothing wrong.
This is good advice. Pixel peepers find problems where there are none 
But in the entirely possible event that you're still going to take a peek anyway, there are two things you can check.
The first (possible) problem is lens alignment when not all the elements are centered correctly. This can happen in manufacture, and is also the most likely problem if a lens gets dropped. I would always do this test when buying a second-hand lens, and the problem shows up most clearly as one or more corners of the image being noticeably softer than the others. You can do the whole thing in under one minute once you get the hang of it. Lens hire firms use this test when lenses are returned.
Check this by selecting a distant subject (to minimise focusing errors) like a road sign or car number plate, in good light. Shoot at lowest f/number and a high shutter speed to avoid any shake, and lock everything in manual so that nothing can change. Take four pictures with the target positioned in each corner of the frame, and make sure the target is exactly the same distance from the edge in each case, as that will make a difference. Also ensure that the light doesn't change between shots as if the sun goes behind a cloud it will make a big difference to apparent sharpness.
If your camera has a good LCD, zoom in on that and check to see if all four corners are all the same. Don't expect to see a high level of sharpness here, because you will not - this is a tough test. What you are looking for is an equal level of sharpness (or unsharpness). If you have to look twice and keep comparing one corner against anhother, there's no problem - if there is, it will be immediately obvious. And don't get too hung up about it - how often is an important part of the subject right in the corner?
The other thing is AF accuracy. The important thing here is not to shoot too close, which is what most folks do in order to see any errros more clearly. All AF systems work to a tolerance, and accuracy varies according to both focal length and focusing distance, so you have to set the best compromise. The problem with shooting close is that lenses are just not designed to be optimum in that situation (unless they're macros) and it's quite likely that there might be a small issue there which does not exist at normal shooting range, and probably doesn't matter much anyway.
The danger is that if you use AF microadjust to correct a close distance error, you will throw it out at normal shooting range. Canon receommends 50x focal length for AF adjustment, but at least 25x should be okay. But in any case, don't go under 3ft. I use this target in my kitchen, and it's as good as anything else costing hundreds of dollars 
Just make sure everything is set up square and position the center AF point close to the rule, say over the 'ta' in this case.
5D2, 17-40L, 50/1.8, 24-105L, 70-200L 4 IS, 580/270EX, Strato II/RF-602, Elinchroms
