| 摘要 |
An f-theta lens includes three lenses in two groups. The first lens group from the entrance pupil side consists of a first lens having a negative or positive refracting power. The second lens group consists of a second lens having a positive refracting power and a third lens having a negative refracting power with the second and third lenses being cemented together. The second lens group has a positive refracting power as a whole. The following formulae (1) to (4) are satisfied. 12</= nu d2- nu d3 (1> -0.035</= SIGMA ( phi i/ nu di)</=0.005 (2> 0.7</= phi 23</=2.0 (3> 0.03</=d12</=0.20 (4> wherein phi i represents the power of i-th lens as numbered from the entrance pupil side standardized on the basis of the power of the whole system, phi 23 represents the power of the second lens group standardized on the basis of the power of the whole system, nu di represents the Abbe's number for the sodium d-line of i-th lens as numbered from the entrance pupil side and d12 represents the surface separation between the first and second lens groups standardized on the basis of the focal length of the whole system. The lens is designed to correct the color aberration, over a wide wavelength range with high accuracy. Use: scanning optical system for color image recording. |
