Mac|Life - February 2009

at this point he’s not far away from capturing the shot, which, as you might guess, isn’t a matter of simply clicking a shutter button. Celestial objects are not only very dim, but also have a pesky habit of “moving” across the sky, thanks to the earth’s rotation. Because of their dimness, Illig’s exposure times can last up to 10 minutes, and to keep his images from blurring, his telescopes have to follow an object’s path very precisely.

This is where the second telescope and yet another camera come in. “That second telescope is mounted atop the imaging telescope in ‘piggyback’ fashion. It, too, has a CCD camera attached,” Illig says, “but it’s a guide camera rather than an imaging camera.”

With his guide camera now communicating directly to his imaging camera via USB, Illig shoots a photo of a star close to his target object, centers that star in the guide camera’s frame, then clicks on it onscreen to identify it in Equinox Image. He now instructs the software to run a calibration routine, during which it moves the telescope in small amounts on the X and Y axes and photographs the guide star, measuring its position relative to the telescope. In essence, the calibration tells the software how to control the movement of the guide camera, while the main camera is simultaneously capturing the target object.

“The telescope mount is now slaved to the Mac software,” Illig says, “so if the guide star begins to move from its original position—a certain pixel on the CCD sensor—the software will move the telescope

Illig inside his cramped observatory. The gray box in the lower right is his main CCD imaging camera. The white machinery in the middle is his computerized telescope mount.

Illig’s observatory from the outside. It’s called Upton Farm Observatory, in honor of his wife Leona’s family farm. It also happens to have the acronym UFO.

to compensate, and the star will remain centered.”

So is it time he snap the shot? Nope. We’re not there yet.

FOCUS, FOCUS, FOCUS. Illig now has to focus the image, which (once again) isn’t as straightforward as it sounds. “I set the camera-control part of the software to Focus mode, in which it takes a series of exposures and downloads them to the Mac for my examination.”