A double-sided telecentric measurement objective for contactless length measurement in two-dimensional and three-dimensional space, said objective comprising:
- two optical systems, each comprising three lenses aligned along an optical axis and constituted of an object-side optical system and an image-side optical system,
- said object-side optical system having in succession from a side turned toward an object:
- a cemented positively refracting lens element and a dispersive cemented surface formed by a convergent lens L.sub.1 with radii of curvature r.sub.1 and r.sub.2 and a thickness d.sub.1 and a divergent lens L.sub.2 with radii of curvature r.sub.2 and r.sub.3 and a thickness d.sub.2,
- a collecting lens L.sub.3 spaced by an air gap of a thickness d.sub.3 from said cemented lens element and having radii of curvature r.sub.4 and r.sub.5 and a thickness d.sub.4 of a highly refractive crown glass, and
- a dispersive meniscus lens L.sub.4 spaced by an air gap of thickness d.sub.5 from said collecting lens and having radii of curvature of r.sub.6 and r.sub.7 and a thickness d.sub.6 ;
- and an image-side optical system having in succession from a side turned away from said object:
- a cemented positively refracting lens element and a dispersive cemented surface formed by a convergent lens L.sub.1 ' with radii of curvature r.sub.1 ' and r.sub.2 ' and a thickness d.sub.1 ' and a divergent lens L.sub.2 ' with radii of curvature r.sub.2 ' and r.sub.3 ' and a thickness d.sub.2 ',
- a collecting lens L.sub.3 ' spaced by an air gap of a thickness d.sub.3 ' from said cemented lens element and having radii of curvature r.sub.4 ' and r.sub.5 ' and a thickness d.sub.4 ' of a highly refractive crown glass, and
- a dispersive meniscus lens L.sub.4 ' spaced by an air gap of thickness d.sub.5 ' from said collecting lens and having radii of curvature of r.sub.6 ' and r.sub.7 ' and a thickness d.sub.6 ' with a convex side turned away from said object;
- widths of air gaps between the respective collecting lenses and the respective meniscuses being substantially greater than widths of air gaps between the cemented lens elements and the respective collecting lenses;
- a back focal point of said object-side optical system coinciding with a front focal point of said image-side optical system so that a reproduction scale of the objective is equal to a ratio of front and back focal lengths of said optical systems, said image-side optical system having substantially the following numerical parameters wherein n.sub.e and .nu..sub.e are respectively the refractive indices and Abbe numbers of the respective lenses:
- ______________________________________ Lens Radius Thickness n.sub.e .upsilon..sub.e ______________________________________ r.sub.1 ' = 130.882 L.sub.1 ' d.sub.1 ' = 9.60 1.4891 70.2 r.sub.2 ' = -22.140 L.sub.2 ' d.sub.2 ' = 2.00 1.6072 37.8 r.sub.3 ' = -127.464 d.sub.3 ' = 3.10 r.sub.4 ' = 40.965 L.sub.3 ' d.sub.4 ' = 5.70 1.6413 55.1 r.sub.5 ' = -597.046 d.sub.5 ' = 13.50 r.sub.6 ' = 28.247 L.sub.4 ' d.sub.6 ' = 11.39 1.5848 40.6 r.sub.7 ' = 15.845 ______________________________________
- focal length:
- 57
- distance to back focal point:
- 23.20.