OK, I have it. Don, the specs answer a lot of questions. It's a small sensor, only 5.59mm x 4.68mm. SONY ICX404AL CCD, in a small array of 510 x 492 pixels. The pixels themselves are on the large side at 9.6um x 7.5um. Here's a quote from the specs page, under sensitivity: "Typically, the NexGuide can capture and guide a star with up to the magnitude of 8 under the following conditions: Regular 80mm aperture refractor, 2048ms exposure time, and good seeing conditions." The Exposure times available are: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096ms. Here's the formula for angular resolution in arc seconds, for any particular guidescope used: 206.265/FL x Pixel size (mm) Back in the old days of hand-guiding when imaging at longish EFL's, the rule of thumb was to guide at twice the focal length of the imaging telescope. CCD's sure have the eye-brain-conscious-reaction system beat, hands down.