Celestron M42 Spacer Kit Spacer Ring Kit for astroimaging purposes Adjusts back-focus between your camera and telescope for the best astroimaging results Kit includes 3 spacer rings of different lengths (7.5 mm, 12 mm, and also 30 mm) Threads to your T-Ring and T-Adapter with standard male and female T-Threads 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. They are made so as to be compatible with M42 x 0.75 (T-thread) camera adapters. 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: 25 mm. Back-focus consumed by ZWO ASI 183 MC PRO camera: 17.5mm - To achieve equal back-focus distance, a 7.5 mm M42 spacer ring is required. Depending your method of astrophotography (DSLR or CCD/CMOS), there are two ways to use the M42 Spacer Rings. If you are using a DSLR, place the desired M42 Spacer Ring between your T-Ring and your T-Adapter for your optical tube. If you are using a CCD or CMOS camera, place the desired M42 Spacer Ring between the camera and the T-Adapter for your optical tube. These suggestions assume you are working with standard camera equipment for astronomical imaging applications. The M42 Spacer Rings are machined aluminum and then black anodized. The internal surfaces are blackened and glare-threaded to provide the highest contrast. Each spacer ring has a knurled surface, providing a great gripping surface for threading/unthreading. The M42 Spacer Rings are made so as to be compatible with M42 x 0.75 (T-thread) camera adapters. The 7.5 mm Spacer Ring works best with the RASA 8 for many ZWO cameras. The 12 mm Spacer Ring works best with RASA 8 for many Atik cameras. The 30 mm Spacer Ring works best with ZWO camera and a filter slider attached, to convert to 55 mm back focus, with standard Schmidt-Cass scopes and with EdgeHD scopes. Camera may be shown in photo for illustration purposes, only, camera is NOT included. Specifications: Spacers: 3 each M42 type T-Thread Spacers Thread: M42 x 0.75 mm Spacer lengths: 7.5 mm (.29"), 12 mm (.47"), 30 mm (1.18") Construction: Aluminum black anodized Interior: Blackened and glare threaded Exterior: Knurled grip surface, each ring labeled with its length
