JPS6428608A - Variable power optical device equipped with focus detecting means - Google Patents

Abstract

PURPOSE:To perform high-accuracy focus detection without causing variation in the accuracy of focus detection even by power conversion for the two-dimensional measurement of an object by providing an objective and a relay lens, an optical path composing member and an optical path shield member, etc. CONSTITUTION:An object image by the objective 1a is formed through a 1st optical path, and further enlarged by the relay lens 6 through a 2nd optical path, and both optical paths are switched to perform power variation. Therefore, the possibility of an optical shift accompanying the power variation is small as compared with power variation performed by changing the lens 1a itself. Then when luminous flux for focus detection projected on the object through the lens 1a is photodetected through the lens 1a, the luminous flux for focus detection is extracted from the 2nd optical path for forming a high-power image, so the accuracy of the focus detection is held high irrelevantly to power switching. Further, the optical path composing member 3 which puts the 1st and 2nd optical paths together is provided and the power switching is performed by optical path shield members S1 and S2 which shields both optical paths alternately, thereby precluding an error such as an optical path shift.