jump

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jump

The displacement of the image of an object occurring when viewing across the borderline between two portions of different power in a bifocal or trifocal lens. The jump is eliminated by placing the optical centres on the dividing line; the lens is then called a no jump bifocal (e.g. a monocentric bifocal with a straight dividing line) (Fig. J1). Syn. image jump; prismatic jump. See monocentric.
Fig. J1 Image jump upward caused by the segment of a bifocal lens, as the direction of gaze is lowered across the dividing lineenlarge picture
Fig. J1 Image jump upward caused by the segment of a bifocal lens, as the direction of gaze is lowered across the dividing line
References in periodicals archive ?
Latest outing from the Johnnie To/Wai Ka-fai factory, hot on the heels of their romantic comedy "Turn Left Turn Right," starts out gangbusters but jumps the rails halfway before an only partly satisfying finale.
DV-lensed urban odyssey, set during a single 24-hour spell, is not without a few longueurs and jumps the rails in its final 15 minutes but still comes out strongly on the credit side overall.
Still, until it jumps the rails in the final reels, this is a workmanlike, sometimes effective serial-killer crime drama with limited theatrical potential in East Asia and almost none in Western markets.