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 ?
The types of fence required to use safety flags include, corners; fences of less than 3m jumpable width; related fences which because of their design offer a jumpable line of less that 3m width; fences where a horse might jump close to a flag and fences jumped on an angle where knocking a flag is a possibility.
60) Alison Brooke Rubenstein, The Whole World is Jumpable, Except
It's also a boom time for musos, with compilation CDs a plenty aiming to capture the mood,and the statisticians (whocan spot a jumpable bandwagon at 100 paces) have got in on the act too.