5- Take test shots
This is by far the most important test. I would take at least 100 test shots minimum. You’re going to want to go through all the various focal length of the lens. While you’re going through the various focal lengths make sure that you take focus shots far medium and near.
6- Go Back To Your Computer And Examine The Images
Finally don’t buy the lens on the spot. Make sure you go back to your computer and examine the images thoroughly for any signs that something may be wrong with the lens. You can watch the video below to see Matt Granger go through these steps in detail.