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Pictor Zoom series lenses will all go through flange back test with shims based on S35 standard before shipping, but flange back distance can vary on different cameras. If the flange back distance is incorrect, the camera will not focus at the correct distance. How to Adjust Back Focus of Pictor Zoom start with, prepare a Siemens Star chart, or other black-and-white (high-contrast) resolution chart to test; your Pictor Zoom lens to the camera; the iris to wide open; up Siemens Star chart at (4.9 Feet) away from the camera (flange), and make sure the target is in the image center. A. Zoom in to the longest focal length, focus on the target until the target is sharpest, and mark down the focus distance as S1. B. Zoom out to the widest, focus on the target until the target is sharpest, and mark down the focus distance as S2. the figure S2 ＜ S1, increasing shim(s) is needed; If S2 ＞
