Method and measuring system for determining the effective focal length of an optical system

A method for determining an effective focal length of an optical system, the method comprising:

• a) arranging an optical measuring device in an image-side focal plane of the optical system;
• b) directing an input beam from an object side of the optical system onto the optical system at a first angle α1 relative to a direction of an object-side optical axis, and determining a first lateral position (x1, y1) of a first point of incidence of a first associated output beam on the optical measuring device;
• c) directing the input beam from the object side onto the optical system at a second angle α2 relative to the direction of the object-side optical axis, the second angle α2 being different from the first angle α1, and determining a second lateral position (x2, y2) of a second point of incidence of a second associated output beam on the optical measuring device;
• and
• d) determining the effective focal length EFL of the optical system from a mutual distance ΔL=√{square root over ((x2−x1)2+(y2−y1)2)} between the first point of incidence the first output beam and the second point of incidence of the second output beam, and from a formula ΔL=EFL*tan(α2−α1).