| 摘要 |
PROBLEM TO BE SOLVED: To remove laser beams of plural wavelength by arranging two filters for removing the laser beam on the positions on which the incident angle and the exit angle of a principal ray are different in an optical path of an optical system. SOLUTION: Laser cur filters 3, 4 for removing a laser beam are arranged in an objective optical system 1 and an infrared absorbing filter 7 is arranged between the laser cut filters 3, 4. An off-axial principal ray 5 is made incident on a diaphragm 1c in the state that an angle to the optical axis is smaller by a 1st negative lens 1a and a 2nd positive lens 1b. The laser cut filters 3 is arranged just after the diaphragm 1c, the incident angle of the principal ray to the laser cut filters 3 isθ3 . A joined positive lens 6 having a refractive power is arranged on the exit side of the infrared absorbing filter 7, the angle of the principal ray becomes moreover smaller and the ray is made incident on the laser cut filter 4 at an angleθ4 .
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