I'm often asked what is needed to connect our SBIG Aluma AC4040 Ultimate Package to a telescope, such as a PlaneWave CDK20 or CDK24. You can calculate the backfocus of the SBIG items using the backfocus calculator spreadsheet on the main page, DOWNLOADS section for your camera. Or click here: https://diffractionlimited.com/downloads/BackfocusCalculator.xlsx Typically you will have a table like this: Aluma AC4040 Camera 0.855in 21.7mm Filter Wheel, AFW Series 0.550in 14.0mm Filter 3 mm thick -0.039in -1.0mm StarChaser SC-3 0.870in 22.1mm Adaptive Optics AO-X 1.049in 26.6mm ======================================== Total Backfocus 3.285in 83.4mm On the PlaneWave side, they have a standard SureFit adapter plate that uses the 4-inch bolt circle we have for the STX10018 adapter plate that camera with the camera - you don't need this, and can save some distance. You likely will need a setup like these parts from PlaneWave: IRF-90 Focuser / Rotator 600327 SureFit Adapter 600328 SureFit Adapter 200395-3 Adapter for Fingerlake Cameras to SecureFit Spacer 3" 600337 Adapter 3"-24 female to SBIG AO-X/STX-FW bolt-pattern The 600337 is the "magic" that adapts to your SBIG stack of equipment. It replaces the 10018 adapter we provide. It fits the top of the AO-X, or SC-3, or AFW or FW7-STX, or AC4040/2020/STX/STXL. Both SBIG and another brand of cameras use the same 3-inch x 24tpi thread size, however you can save space using the SBIG and PlaneWave parts mentioned above.