TESSAR TYPE LENS HAVING BEHIND-DIAPHRAGM

摘要

PURPOSE:To obtain brightness of about F3.5 by a wide-angle lens whose lens shape and telephone ratio are both small, by constituting it of three groups of positive, negative and positive lenses, giving a large refractive index and a small refractive index to the cemented positive lens in the first group and the negative lens, respectively, and obtaining a small telephone ratio. CONSTITUTION:A titled lens is formed by three groups and four pieces of the first group of a meniscus positive lens as a whole, the second group of a binegative lens and the third group of a bipositive lens, by adhering of the positive and negative lenses from an object side. Also, when a composite focal distance of the whole lens system and its composite thickness, a focal distance of the first group positive lens and its composite thickness, a refractive index of a (d) line, its Abbe number, a radius of curvature of the first surface, a refractive index of a (d) line of the negative lens, its Abbe number, an air interval between the second group lens and the third group lens, a refractive index of the third group positive lens, and its Abbe number are denoted as (f), Zd, and f1 and d1+ d2, n1, nu1, k1, n2, nu2, l2, n4 and nu4, the titled lens is constituted as a lens system which satisfies said each condition.