Celestron M42 Spacer Ring Kit

To achieve the best astroimages, it is important to attain the proper back-focus distance for your camera relative to the telescope it is being used with. If the back-focus distance your camera consumes is not exact, the performance at the corners of full frame imaging sensors will suffer—stars will appear elongated and not as pinpoints.

Example: RASA 8 with a ZWO ASI 183 MC PRO camera

Required back-focus distance for RASA 8 with included M42 camera adapter: 25mm

Back-focus consumed by ZWO ASI 183 MC PRO camera: 17.5mm

To achieve equal back-focus distance, a 7.5mm M42 spacer ring is required

Celestron’s M42 Spacer Ring kit includes three different length spacer rings to achieve the proper back-focus distance with our popular Celestron optical tubes and T-thread camera adapters.