Imaging with long focal length instruments, such as with Celestron SCT and EdgeHD optical tubes, requires accurate guiding. An off-axis guider (OAG) is often preferred to be used when doing astrophotography with such instruments. An OAG 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 and any movement of the guide star seen by the guide camera will be the exact same movement seen by the imaging camera. Using a separately mounted guide telescope may introduce flexure. Guiding "off-axis" way will correct for tracking errors, as well as opto-mechanical errors or flexure. The result will be better astroimages with pinpoint round stars.
Off-Axis Guiders have been around for a long time, but typically pose three main challenges:
- Finding a guide star from the far edges of the telescope’s focal plane can be difficult, considering the small field of view/small prism size and sometimes less-than-ideal illumination.
- Getting both imaging camera and autoguider to reach focus with one another is time consuming and sometimes requires experimentation.
- Additional spacers and adaptors 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:
- Providing a large 12.5 mm prism (larger than competing OAG's) that can be adjusted to move closer to the centre 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.
- 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.
- Including all the needed spacers and adaptors are included for most common imaging telescope-camera configurations, including DSLR cameras, CCD cameras, and more.
The Celestron Off-Axis Guider comes with the following adaptors (see image below):
- female M48,
- female M42 (T-thread),
- male M48,
- male M42 (T-thread),
- 3 T-thread spacers
- Helical Focuser Travel: 8 mm
- Telescope Connection: M42 T-thread, M48, and SCT/EdgeHD
- Autoguider Connection: M42 T-thread, and standard 1.25" adapter
- Camera Connection: M42 T-thread, and M48
- Weight 18 oz (510 g)
- Clear Aperture 48mm (1.89")
Off Axis Guider Manual