11
ZOOM LENS BACK FOCUS ADJUSTMENT
The objective of back focusing a zoom lens is similar to that of a fixed
focal length camera except the back focus is also adjusted to maintain
the focus when “zooming” the lens in and out on a scene.
1.
Choose an object at the farthest range set for viewing with a zoom
lens.
2.
Make sure the iris of the lens is wide open. Do this by adjusting the
camera at night or use a welders glass in front of the lens.
3.
Adjust the focus to the stop on the far range.
4.
Adjust the zoom on the lens to obtain the widest picture.
5.
Loosen the back focus lock screw.
6.
Adjust the back focus ring for the clearest picture.
7.
Tighten the back focus lock screw.
8.
Adjust the zoom on the lens to the far telephoto position.
9.
Adjust the back focus ring for the clearest picture.
10.
Adjust the zoom on the lens back to the widest picture.
11.
Loosen the back focus screw.
12.
Re-adjust the back focus for the clearest picture.
13.
Tighten the back focus lock screw.
14.
Repeat the previous steps as necessary to maintain a clear picture
throughout the entire zoom range.
