| Self-Guiding < Return to product view No telescope drive system is perfect. All have small flaws in their drive gears that cause the telescope to speed up or slow down periodically. These drive train errors (and gradual declination drift from not being precisely aligned on the celestial pole), can cause the stars in long exposure photographs to develop small tails or elongate unnaturally. For the sharpest long exposure photos, the telescope should be guided during the exposure, speeding up or slowing down the drive to compensate for the unavoidable unwanted telescope motions as they happen. Many SBIG CCD cameras are self-guiding, making the telescope’s right ascension drive and declination drift error corrections automatically during the course of a long exposure. This means that you don’t have to stay glued to a crosshair guiding eyepiece during the entire exposure to correct for those errors manually. You can even leave the telescope entirely, letting it guide and take its photographs automatically.  The self-guiding SBIG cameras use two CCD detectors, one is a Kodak 657 x 495 pixel TC-237H detector for guiding, while the other is a larger detector for collecting the image. The detectors are mounted in close proximity to each other within a single camera body. Both are focused at the same image plane. This patented guiding method allows you to focus both taking and guiding detectors simultaneously. Some competitive cameras have a separate guiding detector that mounts in an off-axis guider body. This two-housing system requires more setup time to focus each detector independently than does the one-time focus of the SBIG cameras. Still other cameras have one detector, but use a portion of that detector to guide while the balance of the detector collects the image. By using a completely separate internal CCD for guiding, the SBIG cameras allow 100% of the imaging CCD to be used to collect the image, an improvement over other single chip designs. In SBIG tests performed under moderate light pollution with an 8” f/6.3 telescope, randomly pointing the telescope with a self-guiding SBIG camera in it toward objects in relatively star-poor areas of the sky away from the Milky Way resulted in stars on the guiding detector being bright enough to be used for guiding 95% of the time. TheSky software from Software Bisque (supplied with each camera) can print finder charts showing the correct placement of the guiding detector’s field of view relative to the imaging CCD’s field of view. Using this software tool to plan your nights imaging will help you orient the camera for proper guide star acquisition in those few cases where a bright-enough guide star might not be immediately apparent. < Return to product view | 
