Afocal Assembly Focus.
The narrow field-of-view (NFOV) and the wide field-of-view (WFOV)
lens assemblies (Figure 2-9) are mounted on the same housing.
focus coupling connects the range focus knob to the bevel gear. The
bevel gear meshes with and drives the screw and shaft assembly.
screw and shaft assembly is screwed into the focus nut which is
secured to the focus frame. Rotation of the range focus knob causes
the screw and shaft assembly to move the focus frame (with attached
lens assemblies) longitudinally, adjusting the viewed image focus.