| 摘要 |
PURPOSE:To constitute an f.theta lens in compact to reduce production cost and obtain image forming performance approximating the diffraction limit by a wide scan field angle by combining two lenses so that prescribed various conditions are satisfied and forming the f.theta lens thereby. CONSTITUTION:The f.theta lens consists of the first lens having a negative refracting power and the second lens having a positive refracting power which are arranged in order from the beam deflector side, and they satisfy conditions (1) 0.20F0<=L<=0.25F0, (2) -0.80<=R2/F0, (3) 1.70<=N2, and (4) 1.70<=¦F1/F2¦<=2.0 where L and F0 are the overall length and the focal length of the lens system respectively and R2 is the radius of curvature of the first refracting face from the beam deflector and N2 is the refractive index of said second lens for 780mm wavelength and F1 and F2 are focal lengths of said first and second lenses respectively. Thus, the f.theta lens of high performance is obtained with only two lenses. |
