Accessory · MSRP $18 ZWO M42-M48 Extender 16.5mm ZWO · M42-M48 Extender 16.5mm Key specifications Accessory typeAdapter Path length16.5 mm All specifications InterfaceM42 / M48 About 16.5 mm M42-to-M48 extender used to reach a 55 mm back focus distance.