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By Hank Russell
Tracking moving objects through a lens can be tricky. Focus breathing — in which the focus element moves in and out — gives the image a zoom effect as it moves from one end of the focus range to the other. “The actual size of the image will change, and that, in some applications, can be objectionable,” says Dave Waddell, marketing manager, Fujinon Broadcast and Communications Products Division (Wayne, NJ).
Waddell says there are two ways to reduce or eliminate focus breathing. “For a mechanical application, you design the lens to have very little movement in the focus group when you focus to reduce the breathing,” he says. “For the larger lenses that are servo-controlled, as far as focus and zoom go, we use a computer. The computer monitors the focus position and, as the focus is changed, it tells the zoom to zoom in the opposite direction, which effectively cancels out the zooming effect, so the breathing is virtually eliminated.”
Fujinon’s lenses with the longer focal lengths now feature image and optical stabilization systems. “That way, there is no movement in the image,” Waddell says. “Movement, of course, will reduce resolution, so the optical stabilization has been a big factor in very long focal length telephoto lenses.”
Getting a Look
The DIGI SUPER 100xs from Canon (Lake Success, NY) is used for both standard definition (SD) and high-definition (HD) television applications. It has a 9.3~930-millimeter (mm) focal length range (1860 mm with Extender), which is complemented by the company’s built-in Optical Image Stabilization (Shift-IS) system. The Shift-IS system provides viewers with shake-free images — even at extreme telephoto distances. The DIGI SUPER 100xs is a triple-digit zoom lens that incorporates the company’s second-generation Digital Servo System. It provides microcomputer compensation of lens focus breathing and other digital operational features for focus and zooming control. www.usa.canon.com.
Edmund Optics’ (Barrington, NJ) Megapixel Finite Conjugate Micro Video Lenses consist of several precision glass elements mounted in a compact, aluminum housing. They can accommodate pixel counts up to 1.35 megapixels on a 1/3-in. sensor and 2.41 megapixels on a 1/2-in. sensor, making them suitable to smaller format cameras. edmundoptics.com.