Telecentric lens system and vision measuring instrument

1. A telecentric lens system comprising:

a front lens group;

a rear lens group having a front focal point coinciding with a rear focal point of the front lens group; and

diaphragm mechanisms, each of which is disposed at a position where the rear focal point of the front lens group coincides with the front focal point of the rear lens group, wherein

one of the front lens group and the rear lens group includes a plurality of variable magnification lens groups,

the diaphragm mechanisms are provided corresponding to the plurality of variable magnification lens groups, respectively, and

a magnification switching mechanism is provided to selectively move a pair of one of the plurality of variable magnification lens groups and one of the corresponding diaphragm mechanisms to be disposed on an optical axis of the other of the front lens group and the rear lens group, wherein

the magnification switching mechanism includes a slide plate, a guide mechanism that supports the slide plate to be slidable in a direction approximately orthogonal to the optical axis of the other of the front lens group and the rear lens group, and a magnification switching unit for sliding the slide plate,

a plurality of pairs of the variable magnification lens groups and the corresponding diaphragm mechanisms are arranged in the sliding direction of the slide plate,

each of the diaphragm mechanisms includes a numerical aperture changer including: a first diaphragm disposed on the optical axis of the other of the front lens group and the rear lens group; a swing lever having a middle portion supported to be swingable and an end supported to be retractable from a position of the first diaphragm; and a second diaphragm formed on the end of the swing lever and having a smaller diameter than a diameter of the first diaphragm, the numerical aperture changer changing a numerical aperture by switching the first diaphragm and the second diaphragm,

a numerical aperture switching unit is provided to rotatably connect a base end of the swing lever of the diaphragm mechanisms and swing the swing lever thereof about a swinging supporting point, and

the magnification switching unit and the numerical aperture switching unit are provided on the slide plate to protrude in directions parallel to the sliding direction of the slide plate, the directions being mutually in a same direction.

2. A vision measuring instrument, comprising:

a telecentric lens system according to claim 1 ; and

an image pickup optical system connected to the telecentric lens system.

3. A vision measuring instrument, comprising:

a telecentric lens system according to claim 1 ;

an illumination optical system introducing light into the telecentric lens system;

magnification detection units that detect a magnification switched by the magnification switching mechanism;

numerical aperture detection units that detect a numerical aperture switched by the numerical aperture changer;

an image pickup optical system connected to the telecentric lens system; and

an image processor that processes image information obtained by the image pickup optical system, wherein

the image processor performs at least one of an illumination condition correction of the illumination optical system, a magnification correction of the variable magnification lens groups, and an axial alignment in accordance with the magnification detected by the magnification detection units and the numerical aperture detected by the numerical aperture detection units.