I have read a number of articles that discuss the focus shift problem with this lens. The only response I have seen from Canon was extremely brief and said that it was a design decision. I must be missing something because I cannot imagine any reason to buy any lens that exhibits focus shift as the lens is stopped down. The only work around that I have seen is to take a photo and, if it is out of focus, then manually focus in front of the desired focus point and use focus bracketing to take a series of photos and pick the one that has the desired point in focus. Why would I (or anyone) buy this lens instead of keeping their EF-100mm macro and sticking an adapter on the back. What am I missing?