Off-axis guiding is the most accurate way to guide, with improved accuracy compared to using a separate guide scope. Celestron’s #93648 Off-Axis Guder (OAG) unit is very well made and features a large 12.5mm multi-coated pick-off prism, helical focuser for the guide camera and full 360-degree rotation about the optical axis in order for the guide camera to pick up a suitable guide star. You can read more on this unit in two of our earlier blogs here and here.
If you have a larger aperture SCT or EdgeHD scope (i.e. 9.25″ and above) and would like to make full use of the telescope’s image circle with a full frame DSLR/large sensor imaging camera, for better illumination of the imaging sensor, then Celestron’s Large SCT/EdgeHD Off-Axis Guider telescope adaptor will come in useful.
This is a one-piece black anodised aluminium adaptor that is substituted in place of the SCT adaptor that is supplied as standard with the OAG unit. The adaptor has a (larger) 62.7mm clear aperture, takes up only 16mm of back focus and weighs 131g. As with the SCT adaptor that is supplied with the OAG, the camera side of the adaptor has a dovetail profile to allow secure fitment when the OAG body locking screws are tightened and also allows the OAG to be rotated 360-degrees. On the telescope side there is the larger diameter SCT thread for attaching to the large baffle lock nut on the back of the SCT/EdgeHD OTA (or on the rear of the appropriate EdgeHD 0.7x focal reducer).