| 摘要 |
PROBLEM TO BE SOLVED: To provide a light-receiving optical system which accurately narrows down only a required wavelength region and suppresses light quantity loss.SOLUTION: The light-receiving optical system includes: a light source for emitting light in a prescribed wavelength region; a light-receiving lens 10 for condensing the light; and a diaphragm 20 which is arranged at such a distance from the light-receiving lens 10 that a diameter of a beam of the light in the prescribed wavelength region is smallest, and is formed so that a diaphragm diameter on the exit side of an aperture may be substantially equal to the smallest diameter. |
