An optical device housing has a post rotatably extending therefrom and a sleeve fixedly extending therefrom. The sleeve is disposed around the post. A knob is connected to the post. A clutch mechanism includes: a friction element movably engaged with the sleeve; a friction surface; and an adjustment element engaged with the friction element and rotatable relative to the optical device housing and the knob housing. Rotation of the adjustment element selectively engages the friction surface with the interior surface.