Imagine heading to a photo shoot and noticing afterward that most images you took are partially out of focus. You are sure you set the focus right, and the depth of field in the photos is also sufficient. The problem might be a decentered lens.

Half of the lenses I bought in the past 15 years were decentered. At first, I didn't know of that problem. The first wide angle lens I got from Canon required focus-stacking all the time. Since I mostly shot landscapes, it wasn't clear to me that this was due to a problem with the lens and not because of the topography of the landscape or the...