OPTICAL IMAGING SYSTEM

摘要

Optical imaging system between an object plane (2.2) of a total reflexion prism (2) and an image plane, mainly for a fingerprint reading apparatus, that comprises an optics (3) for imaging the object plane to the image plane, and an electronic image detector (4) in the image plane. The optics defines an optical axis (3.0) and input and output pupils, respectively. The total reflexion prism (2) is arranged in front of the input pupil of the optics (3). The prism has a first surface receiving light for illuminating the object plane through the interior of the prism and a further surface through which light reflected from the object plane passes towards the optics. The object plane closes an angle with the optical axis, which is preferably between 45~ and 65~ if the refraction index of the prism is between 1.5 and 1.85. The object plane (2.2) of the total reflexion prism (2) is offset relative to the optical axis (3.0) in normal direction and the image detector (4) is also offset in normal direction relative to the optical axis (3.0) to an extent which corresponds to the location of the image of said object plane.