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 ?
Jump For Joy makes two classes of jump, one of hollow plastic for private use at home and a competition class, which consists of a wooden rod surrounded by plastic which is already being used by the British Show Jumping Association.
JUMP FOR JOY: Pupils celebrate at Kensington's Sacred Heart Catholic primary school, which the judges visited
victims--but it hardly makes me jump for joy to realize that
Headteacher Kevin Doran said: "The report quotes parents as saying their children 'Jump for joy' on school days.
Most of us wouldn't jump for joy at the prospect of spending 40 days and 40 nights with a bunch of chaste nuns.