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 ?
Film's carefully controlled rhythm starts to jump the rails in the final 20 minutes, with some emotional outbursts that don't ring true and an over-long finale in which all the passengers (German and otherwise) are united singing a verbal riff on a famous choral passage from Verdi's opera "Nabucco.
Hereon, however, the movie starts to jump the rails, as Pedro reappears as a ghost in Phillip's imagination, the kid falls in with some weird teen neighbors (James Befiand, Paz De La Huerta), and Dad turns up to put the seal on mother and son's fledgling domesticity.