| 摘要 |
PURPOSE:To obtain an object lense suitable for the compound lens which makes the emitted light of a solid light emitting element such as a semiconductor laser into a parallel luminouxs flux, by constituting the object lens with four lenses of four groups and forming respective lenses so that relative ratios of the resultant focal length of the whole of the system to focal lengths of respective constituent lenses are within specific ranges. CONSTITUTION:The object lens is constituted with four lenses of four groups, namely, the first positive lens, the second positive lens whose convex face is directed to the object side, the third positive lens whose convex force is directed to the object side, and the fourth positive lens whose convex face is directed to the object side which are arranged in order from the object side, and these constituent lenses are so formed that 3.39<f1/f<4.46, 2.53<f3/f<3.66, and 2.27< f4/f<5.33 are ture. In these inequalities, (f), f1, f3, and f4 are the resultant focal length of the whole of the object lens system, the focal length of the first lens, the focal length of the third lens, and the focal length of the fource lens respectively. Thus, the numerical aperture NA is larger than 0.64, and the object lens has a long back focus. |
