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Classification of zoom lens

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Classification of zoom lens

There are two types of zoom lenses, optical compensation, and mechanical compensation.

In an optically compensated zoom lens, two or more alternate lenses are connected and move together relative to the lens between them. This structure simplifies the mechanical structure and helps maintain good control of boresight and alignment. The

image motion produced by this type of system is a cubic curve, with the image in focus at a specific number of positions during zoom. The maximum number of positions where the longitudinal (axial) image movement is 0 is equal to the number of movable air gaps. If the object is at infinity and the first lens group is moved during zooming, the distance between this lens group and the object is not considered a variable air distance.

In a mechanically compensated zoom lens, a movable element typically provides a change in magnification (or focal length), while defocusing is eliminated by shifting one of the other elements in the zoom system. It is generally found that one or more of these elements need to be driven by some form of continuous zoom cam. Although this arrangement is more mechanically complicated,

However, the imaging has been kept at the focal point within the zoom range, and this type of system often has a shorter overall length than the optically compensated type. Almost all infrared zoom lenses are mechanically compensated

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