| 摘要 |
PROBLEM TO BE SOLVED: To use an image forming lens having a small F value by restricting an expansion angle of the light incident on a transfer optical system by the size of a light emitting area of a light source and a focal distance of a collimator lens in a recess/projection pattern reader for reading a recess/projection pattern such as a fingerprint. SOLUTION: A fingerprint reader 10 has a rectangular prism 12 having a total reflection detecting surface, an illuminating optical system 20 for illuminating a fingerprint 38 as a recess/projection pattern placed outside the total reflection detecting surface from the inside of the total reflection detecting surface 14 and a transfer optical system 28 for transferring a fingerprint reflected image to an image pickup device 30. In this case, the illuminating optical system 20 is provided with a collimator lens 26 for making a light flux emitted from a light source 22 incident on the total reflection detecting surface 14 as parallel light fluxes. When the size of a light mitting area of the light source 22 is (d0), a focal distance of the lens 26 is (f), a maximum optical path difference to the image pickup device 30 in the total reflection detecting surface is (b) and a refractive index of the prism 12 is (n), resolution (m) of the illuminating optical system 20 is set so as to satisfy the expression. |
