If you already have either SBIG ST-i planet cam, the SBIG ST-i Guiding Kit will convert it into a compact, lightweight guiding system that can be used with any telescope/equatorial mount combination that accepts an autoguider input.
The SBIG ST-i Guiding Kit consists of a high quality 100mm focal length f/2.8 lens with locking aperture (f/2.8 to f/22) and focus adjustments, a custom C-mount adapter that connects the autoguider lens to your existing SBIG ST-i color or monochrome imager, custom heavy duty black satin finish rings and a universal mounting plate, plus a lens shade/dew shield that slips over the lens to shield it from unwanted ambient light. The assembled ST-i/Guiding Kit combination is ultra-compact, only 6.5 inches long, and weighs less than 13 ounces (368 grams), including the camera.
The Guiding Kit’s fast f/2.8 lens allows guiding on very faint stars. For example, it is capable of guiding to sub arc second accuracy on stars fainter than 7th magnitude using 1-second exposures. Its large 2.7° x 2.0° field of view means that there will virtually always be a suitable guide star in the field of view, no matter where the telescope is pointed at the sky.
The benefits of this wide field are twofold: first, there is no need to hunt for guide stars, and second, since there is no need to adjust the pointing of the guide scope away from the main scope to find suitable guide stars, the guider can be more firmly mounted to avoid differential flexure. Unlike mounting systems using rings with three-point adjustment screws that can move or flex, the oversized rings of this SBIG Guiding Kit clamp firmly around the body of the ST-i camera and hold it firmly in place. Guide scopes that use adjustable mounting systems are almost always plagued with differential flexure. In comparison, the ST-i guiding Kit is mechanically rock-solid.
The custom mounting rings and universal base plate of the ST-i Guiding Kit provide multiple attachment options for almost every telescope equipped with a piggyback mount or accessory plate that uses a standard 1/4-20 bolt or threaded hole.
In addition to making guiding a complete and easy task, this Guiding Kit also makes the ST-i a very capable electronic finder scope. The ST-i, with its built-in shutter, can take dark frames allowing the useful capture of relatively long exposures compared to other guiders. The fast f/2.8 focal ratio of the SBIG Guiding Kit lens, combined with the high sensitivity and dark frame capability of the ST-i, means that globular clusters and cores of galaxies are within easy reach of this compact system. In tests of the ST-i and Guiding Kit from a typical backyard observatory with average light pollution, stars dimmer than 10th magnitude were detected in 1-second exposures. In 10 seconds, stars dimmer than 13th magnitude were recorded and stars as dim as 15th magnitude were captured in 30 seconds.