Here is a list of adapters for a typical SBIG Aluma AC4040 package with a PlaneWave CDK20 or CDK24 with the IRF90 focuser rotator. This is provided as a convenience; you will need to verify backfocus distances for your particular setup. SBIG Backfocus Calculator Spreadsheet: https://diffractionlimited.com/downloads/BackfocusCalculator.xlsx PlaneWave to SBIG Adapter Plate - use this instead of the SBIG STX 10018 nosepiece that comes with the camera: https://planewave.com/product/600337/ Calculation: Code: SBIG Description Backfocus Backfocus inch mm Camera Model Aluma AC4040 0.855 21.7 Filter Wheel AFW Series 0.550 14.0 Filter 3mm thick -0.039 -1.0 Guider StarChaser SC-4 0.875 22.2 Adaptive Optics AO-X 1.049 26.6 TOTAL REQUIRED: 3.290 83.5 CDK Available Backfocus 14.349 364.5 Back Plate 240343-1 5.300 134.6 Focuser/Rotator IRF90 3.500 88.9 PlaneWave 600327/600328 adapter 0.500 12.7 PlaneWave 200377 extender 0.500 12.7 PlaneWave 3x24tpi 200394-3 0.250 6.4 Focal Reducer None 0.000 0.0 PlaneWave to SBIG 3x24 600337 0.200 5.1 Remaining backfocus 0.809 20.6 Note: You will need to work this out for your equipment and allow for tolerances. Backfocus includes optical backfocus distances. Assumption is focuser is fully racked in - remaining backfocus needs to be sufficient to move to attain focus. Filters have a higher index of refraction than air, so we subtract the RI factor (usually 33% of the thickness).
