jump(redirected from jump the gun)
Also found in: Dictionary, Thesaurus, Legal, Idioms, Encyclopedia, Wikipedia.
Related to jump the gun: keep one's nose to the grindstone
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.