The Celestron Off-Axis Guider is an essential astroimaging accessory for long focal length telescopes that require the most accurate guiding possible. The Celestron Off-Axis Guider uses a prism to intercept a small portion of the telescope�s focal plane (outside the field of view of the main imaging camera) to locate a guide star. Any movement seen by the guide star will be the exact same movement seen by the imaging camera. Guiding this way will correct for tracking errors, as well as opto-mechanical errors or flexure. The result: better astroimages with pinpoint round stars.Off-Axis Guiders have been around for a long time, but typically pose three main challenges:1. Finding a guide star from the far edges of the telescope�s focal plane can be difficult, considering the small field of view and sometimes less-than-ideal illumination.2. Getting both imaging camera and autoguider to reach focus with one another is time consuming and sometimes requires experimentation.3. Additional spacers and adapters are usually required for your particular camera, telescope, and autoguider, which adds to cost and complexity.Celestron's Off-Axis Guider addresses these challenges by:1. Providing a large 12.5 mm prism that can be adjusted to move closer to the center of the telescope�s focal plane, depending on the size of the imaging camera. This results in brighter guide stars, with the help of the large prism to fully illuminate the autoguider sensor.2. Featuring a high-quality, fixed-orientation Helical focuser. This provides extremely smooth and accurate focus of the autoguider without changing (or twisting) the autoguider camera orientation.3. Including all the needed spacers and adapters are included for most common imaging configurations, including DSLR cameras, Nightscape CCD cameras, and more. The following adapters are included: SCT/EdgeHD, female M48, female M42 (T-thread), male M48, male M42 (T-thread), 3 T-thread spacersFeatures- Most accurate way to guide � improved accuracy compared to using a separate guide scope- 12.5mm multi-coated prism with optimised performance for maximum reflectivity and illumination to the autoguider- Fixed-orientation helical focuser for easy, smooth and accurate autoguider focus- 48mm clear aperture supports full frame cameras without vignetting- Includes adapters with the correct spacing for DSLR cameras, Nightscape CCD and other popular astroimaging cameras- Ideal for Schmidt-Cassegrain and EdgeHD telescopesSpecificationsWeight: 18 oz (510 g)Clear Aperture: 48mm (1.89")