| 摘要 |
PURPOSE:To suppress small a variation of various aberrations in a wide image magnification range by constituting a titled lens of five groups and six pieces which consist of the first and the second lenses of positive lenses, the third and the fourth lenses of negative lenses, and the fifth and the sixth lenses of positive lenses in order from an object side, and whose second and third lenses are cemented. CONSTITUTION:A titled lens is constituted of five groups and six pieces which consist of the first and the second lenses of positive lenses, the third and the fourth lenses of negative lenses, and the fifth and the sixth lenses of positive lenses in order from an object side, and whose second and third lenses are cemented. In this state, when (f), f1, f6, d7, -n+ and -nu-, and -n- and -nu+ denote a focal distance of the whole system, a focal distance of the first lens, a focal distance of the sixth lens, an air space of the fourth lens and the fifth lens, a refractive index of the positive lens and a mean value of the Abbe number, and a refractive index of the negative lens and a mean value of the Abbe number, respectively, the conditions of the inequalities are satisfied. In this way, the fourth lens and the fifth lens are separated from each other, and as a result, when a beam which is made incident obliquely passes through the fourth and the fifth lenses, a point which generates a difference in height from its optical axis is utilized, a pincushion distortion is suppressed, and also a variation of a distortion due to a magnification change is suppressed. |
