Apparatus and method for measuring an optical property of an optical system
An apparatus for measuring the MTF or another optical property of an optical system includes an object to be imaged, which has a plurality of structures arranged in a plane and separated from one another, a two-dimensional image sensor, and collecting optics having a focal length f. The image sensor has a distance a from the collecting optics with 0.94·f≤a≤1.1·f. A holder for the optical system is arranged such that the optical system is located in a beam path between the object and the collecting optics. The image sensor and the collecting optics are configured such that all structures can be imaged by the optical system and the collecting optics onto the image sensor simultaneously.
1 . An apparatus for measuring a modulation transfer function (MTF) of an optical system, the apparatus comprising:
an object to be imaged having a plurality of structures arranged in a plane and separated from each other;
a two-dimensional image sensor;
collecting optics having a focal length f, wherein the two-dimensional image sensor has a distance a from the collecting optics with 0.9·f≤a≤1.1·f, and wherein the image sensor and the collecting optics are configured such that all of the structures of the object are imaged by the optical system and the collecting optics onto the image sensor simultaneously;
a holder configured to hold the optical system; and
an evaluation unit configured to determine the MTF by evaluating an image of the object formed on the image sensor,
wherein the holder is arranged as a feed device, in which the optical system and additional optical systems that are similar to the optical system are fed stepwise to the apparatus in an automated quality inspection process, such that the optical system and the additional optical systems are fed so as to be individually located, one after the other, in a beam path between the object and the collecting optics.
2 . The apparatus of claim 1 , wherein the object is an illuminated reticle.
3 . The apparatus of claim 1 , wherein the structures are crosshairs.
4 . The apparatus of claim 1 , wherein the holder is arranged in a diverging beam path.
5 . The apparatus of claim 1 , wherein a collimator is arranged in a light path between the object and the holder.
6 . The apparatus of claim 5 , wherein the collimator is a conoscopic lens.
7 . The apparatus of claim 5 , wherein the object is movable along an optical axis of the apparatus to vary a distance between the collimator and the object.
8 . The apparatus of claim 1 , wherein the image sensor is movable along an optical axis of the apparatus.
9 . A method of measuring a modulation transfer function (MTF) of an optical system, the method comprising the following steps:
providing an object, a two-dimensional image sensor, and collecting optics having a focal length f, wherein the image sensor has a distance a from the collecting optics with 0.9·f≤a≤1.1·f;
inserting the optical system and additional optical systems that are similar to the optical system into a beam path between the object and the collecting optics, wherein a feed device is provided to feed the optical system and the additional optical systems stepwise in an automated quality inspection process, such that optical system and the additional optical systems are fed so as to be individually located, one after the other, in the beam path between the object and the collecting optics;
simultaneously imaging the object within a field of view of the optical system and the collecting optics onto the image sensor using the optical system and the collecting optics; and
determining the MTF by evaluating an image of the object formed on the image sensor.
10 . The method of claim 9 , wherein the optical system has a variable focal length, and wherein the MTF of the optical system is measured for at least two different focal lengths.
11 . The method of claim 9 , wherein the optical system is afocal, and wherein a collimator is disposed in the light path between the object and the optical system.
12 . An apparatus for measuring an optical property a modulation transfer function (MTF) of an optical system, the apparatus comprising:
an object to be imaged having a plurality of structures;
a two-dimensional image sensor that is movable along an optical axis of the apparatus;
collecting optics, wherein the two-dimensional image sensor has a distance a from the collecting optics with 0.9·f≤a≤1.1·f, and wherein the image sensor and the collecting optics are configured such that all of the structures of the object are imaged by the optical system and the collecting optics onto the image sensor simultaneously;
a holder configured to hold the optical system; and
an evaluation unit configured to determine the MTF by evaluating an image of the object formed on the image sensor,
wherein the holder is arranged as a feed device, in which the optical system and additional optical systems that are similar to the optical system are fed stepwise to the apparatus in an automated quality inspection process, such that the optical system and the additional optical systems are fed so as to be individually located, one after the other, in a beam path between the object and the collecting optics.