Navitar 640MCZ275 Installation Instructions page 2

3. To focus, gently twist the front of lens. To zoom, loosen thumbscrew and twist
knurled ring (zoom lenses only, of course). Re-tighten thumbscrew. CAUTION: Do
not twist entire lens out of adapter! On MCZ275 Models, twist the knurled inner ring
to zoom and twist the knurled outer ring to focus the lens.