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ZOOM LENS BACK FOCUS ADJUSTMENT
The objective of back focusing a zoom lens is similar to that of a fixed focal
length camera, except that back focus is also adjusted to maintain the focus
when "zooming" the lens in and out on a scene.
. Choose an object at the farthest range that you wish to look at with a zoom
lens.
. Make sure the iris of the lens is wide open. (Do this by adjusting the camera
at night or use a welder's glass in front of the lens.)
. Set the focus on the lens to the far range.
. Adjust the zoom on the lens to obtain the widest picture.
. Loosen the back focus lock screw.
. Adjust the focus adjust ring for the clearest picture.
. Tighten the back focus lock screw.
. Adjust the zoom on the lens to the far telephoto position.
. Adjust the back focus ring for the clearest picture.
. Adjust the zoom on the lens back to the widest picture.
. Loosen the back focus lock screw.
. Readjust the back focus for the clearest picture.
. Tighten the back focus lock screw.
. Repeat the previous steps, as many times as necessary, to maintain a clear
picture through the entire zoom range.
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