I purchased this lens exclusively for underwater photography use. It is recommended by many UW photography sites and UW photographers as a must have lens for wide angle photography. Although I also have a Canon 10-22 mm lens, I thought I'd give this a try and see what all the excitement was about. Well, they weren't kidding. This is a phenomenal tool for UW photography. I shot this through an 8" Ikelite dome using a Canon 7D. Sharpness was very good, even into the corners. You can get very close to your subject and minimize the water column (and particles) to a greater degree than even the Canon 10-22 mm. The distortion you see with this lens above water is not evident below. I was always a bit nervous about using a fisheye, because of the curvature they yield. I was pleasantly surprised how much this is a non-issue underwater. Depth of field is fantastic, allowing wide angle close ups of a small foreground subject, with an expansive scene behind. Wreck photography under some pretty dirty water conditions was also excellent. I've had a great time exploring new techniques with this lens, such wide angle close-ups at a small aperture and slow shutter speed to give a visible or blue water background. The 10 to 17 mm zoom makes it very flexible for changing subject matter. The only negative I've found is a tendency toward purple fringing. This isn't evident unless you pixel peep, and it doesn't seem to have a practical effect on picture quality, but it is evident if you zoom into some images. You really have to watch strobe position with a lens this wide. Push them too far forward and fire them toward full power and you run the risk of hot spots bleeding into the photo. As you might expect, this is especially true when the water is heavy with particulates. With a little care and practice, this problem is readily avoided. This lens also seems to be a good choice for shooting UW video. The high depth of field this lens offers eliminates focusing concerns on cameras like the 7D. In most cases it is focus once and forget. Overall, this was a great purchase. Particularly when you consider the reasonable price, every serious UW photographer should own one of these.