Just ask André Costantini, who brought the lightweight zoom on an oceanic adventure during a recent trip to Key West, Florida. “I had procured an ewa-marine underwater housing for my digital SLR and figured that was a perfect excuse to try diving,” he says. “I had never dove before, however, and I wasn’t about to spend my entire week getting certified, so I opted for a resort dive.”

Determined to make his second dive more fruitful, Costantini dove to just 30 feet and added air to the housing to help relieve some of that awe-inspiring pressure. He also had to compensate for the optical illusions of the underwater arena. “Because of the characteristics of water on the optical world, I left the camera in autofocus and taped the lens to stay at the 17mm focal length,” he says. “Lenses appear to be one-third less wide down there. As it turns out, objects also appear 1.33 times larger underwater—the focusing distances under water are different then on land.” Interestingly, as Costantini discovered, using autofocus will work, as well as manually focusing underwater. One caveat, however: “If you measured the distance from your camera to the object you were photographing and then matched the focus distance on your lens, the object would not be in focus.”

The 17-50mm’s fast F/2.8 aperture not only allows for experimentation with faster shutter speeds and natural-looking out-of-focus effects on portraits—it also helped Costantini capture one of Key West’s most famous attributes. “Using the Tamron 17-50 on this trip was great,” he says. “It allowed me to have a wide-enough-angle lens to photograph underwater and then rise to the surface and use the fast 2.8 aperture to capture the glorious sunsets Key West has to offer.”