As a pro photographer, I need to work with the best equipment I can to deliver the best possible images to my clients. I’m a Canon shooter and use all Canon L series lenses. The L series is the professional line of lenses that are the sharpest, most rugged, and weather sealed line of lenses that Canon sells. Even so, I tend to be very gentle with my equipment because I rely on it to work when I need it to. All my equipment looks almost new.
And Canon delivers on all of that quality. Usually. The L lenses are as sharp as anything on the market…except for when they’re not. About once a year, I will have a lens that has a glass element inside that shifts and the lens gets soft (i.e. not sharp) at one or more focal lengths, usually on one side of the frame. I’ve had it happen to at least five lenses.
A quick (but not cheap) repair by Canon usually puts the lens back to factory specifications. But it happens seemingly randomly and I am not able to notice until the images are viewed on my computer. I am in the habit of testing all my lenses before a big shoot to make sure everything checks out. I also see this happening to other photographers because I have noticed images in print that show this problem. Once you’ see it, it’s obvious. The images here show the sharp and soft areas (shown by the red boxes in the full image at top) at 100% magnification. Notice how the image on the right gets softer as you view from the left to the right side of the image