JPS5517132A - High contrast objective lens used in finite distance - Google Patents

Abstract

PURPOSE: To heighten the contrast as the objective lens used in finite distance, by constituting in six groups with six lenses having an iris provided between the front group and rear group, and satisfying specific conditional formulae among the lenses.

CONSTITUTION: Sequentially from the object field side, the front group consists of first group comprising a negative single lens L₁, and second and third groups comprising two-side convex single lenses L₂, L₃, and the rear group consists of fourth group comprising two-side concave single lens L₄, fifth group comprising a positive meniscus single lens L₅ having the strong convex face directed to the image field side, and sixth group comprising a positive single lens L₆ having the strong convex face directed to the image field side, and an iris S is provided between the front group and rear group in this six-group, six-lens constitution. Conditional formulae 1 to 5 are satisfied simultaneously in all lenses. Thus is obtained a lens of which MTF is more than 0.65 over the entire screen, ratio of peripheral quantity of light is more than 80% even in the corners of the screen, distortion aberration is less than ±1% even in the final side, and back focus is about 1.0f. (d is the air gap on the axis; n is the refractive index; and ν is the Abbe number).

COPYRIGHT: (C)1980,JPO&Japio