What are helical focusers and why does Borg use them?
Helical focusers work by turning a ring to focus as we do when using a conventional camera (at least in manual focus mode). A true helical focuser works like a camera — when you turn the focusing ring, neither the lens nor the camera (or eyepiece and diagonal) rotate. The only motion is in and out. Some manufacturers implement a “pseudo-helical” focuser which results in a rotating camera or eyepiece, but Borg focusers are true helical focusers. The advantage of helical focusers is the fine adjustment possible, in part due to the fine pitch of the focusing ring’s thread, and in part due to the large diameter of the ring. In the case of the Borg helical focusers, virtually backlash-free movement and graduated markings on the focusers allow repeatable return to the focus point simply by noting the focus position reading.
