Hello, thank you for the reply and the diagram. Unfortunately for my Takahashi Epson 180, I need 56.2mm back focus. The ASI6200 (17.5mm), Filter wheel (20mm), CAA (16.50mm), Male-to-Male 54mm ring (1.8mm) and Light masks (.4) adds up to 56.2mm. That leaves zero space for any extension rings.