Celestron’s RASA 8″ has become a very popular (imaging) telescope. Its low weight (~7.7kg) and relatively small size means that wide field, fast (F/2) imaging can be done by anyone with one of the popular low cost mid-range German EQ mounts.
For imaging with the RASA you can use a dedicated astronomy imaging camera or one of the increasingly popular mirrorless cameras. Celestron offers two mirrorless camera adaptors for their RASA 8 telescope – the #93405 is for Sony mirrorless cameras and #93406 is for Canon mirrorless cameras. These adaptors allow you to connect a Sony or Canon mirrorless camera to the RASA 8, and place the camera’s sensor at the proper position relative to the RASA’s optics (i.e. at the proper backfocus distance”) with no other adaptors or spacer rings being needed.
With an increasing number of mirrorless models becoming available from each manufacturer, it has come to Celestron’s attention that the hand grips on the newer Sony and Canon bodies are too close to the lens mount, which causes mechanical interference between the hand grips and the RASA camera adaptors. Celestron have therefore released compatibility information to help you see if your camera (or potential purchase of a camera) will work with a RASA 8″:
- Is compatible with Sony α5 and α6 E mount models
- Is NOT compatible with Sony α7, α9, or A mount models
- Is compatible with Canon EOS M200, EOS M100, and EOS M10 models
- Is NOT compatible with Canon EOS R/RP/Ra, EOS M6/M5/M3, EOS M50
Celestron have stated that you can still use an incompatible camera model with the RASA 8, but you will need to purchase a custom camera adaptor from a third party rather than using the Celestron adaptors. However, it is important to note that It will be difficult (if not impossible) to create an adaptor for one of these incompatible mirrorless cameras without causing some vignetting (i.e. light loss) at the corners of the frame. This is because the camera adaptor will need to be designed narrower (i.e. with a smaller diameter) than the Celestron adaptor to prevent the mechanical interference, which will block some of the light collected by the RASA 8 from reaching the edges of the sensor.
Furthermore, the RASA was designed with a 32mm usable image circle, so any Sony or Canon mirrorless camera that uses a full frame sensor (i.e. 43mm diagonal) will have some vignetting and performance loss at the edge of the frame regardless of the camera adaptor with which it is used.