It requires an off-axis guide camera behind the AO; typically the SBIG StarChaser SC-4 is used. The AO-X is compatible with the Aluma AC4040, Aluma AC2020, and Aluma AC455 cameras, when used with a StarChaser SC-4. AO-X is also compatible with older STX-16803, STXL-16200, STXL-...