This 15 mm extension tube fits between the focuser, the existing 10 mm extension and the main tube on the F50G Guidescope. Referring to the picture below, simply un-thread the focuser with its attachment ring and thread this 15 mm extension to the existing extension. Then replace the focuser.
Different guide scopes have different back focus requirements. We machined this part to help optimize our guidescope for different cameras. Made in the USA on our cnc machines using 6061 T6 aluminum.