View Slideshow Trevor Paglen's subjects are good at keeping secrets — and their distance: Many miles of secure federal land frequently surround the off-limits military installations that he goes to great lengths to photograph. To zoom in on them, Paglen — a photographer and geography buff — developed what he calls limit-telephotography. It's a hack based on astrophotography, a technique normally used to shoot distant planets. "It's much more difficult to take a picture of something on the ground than of something trillions of miles away," he says. Paglen modded the lens mount on his standard-issue Canon digital SLR to accept high-powered telescope lenses ranging in focal length from 1,300 mm to 7,000 mm (a typical telephoto is about 300 mm). To capture the heavens, such lenses peer through at least 5 miles of relatively dense atmosphere. Aimed at terrestrial subjects, they magnify and distort the up to 65 miles of air, dust, and smog that hovers between camera and subject. The resulting shots, some of which go on exhibit in July at the Yerba Buena Center for the Arts in San Francisco, are hazy abstractions that expose a certain truth, yet leave everything to the imagination. View Related Slideshow: "Off-Limits But Not Out of Sight"