Common imaging train

Askar FRA400 + OAG-L-68 + EFW 7×36 + ASI2600MM Pro

The FRA400 is a Petzval with the flattener built in: Askar states a maximum connection length from the end of its M68×1 rotator thread, not a fixed spacing. The FRA400 ends in an M68 thread, which is exactly what the OAG-L-68 was made for: it bolts the wheel and camera straight on without a step-down ring, keeping the full 44 mm image circle open. The tool reports how much of the maximum connection length is left for the focuser — a lot, on this tube.