To attain a reading lens which has a large aperture nearly the same as that of the conventional one, achieves a much wider viewing angle and also excels in performance.
The reading lens is constituted by arranging, in order from an object side to an image side, a first positive group, a second negative group, a third negative group, a fourth positive group, a fifth positive group, and a sixth negative group, and providing an aperture stop between the second group and the third group. The reading lens is composed of seven lenses of six groups, that means, the first group has a first positive lens L1, the second group has a cemented lens composed of a second positive lens L2 and a third negative lens L3, the third group has a fourth negative lens L4, the fourth group has a fifth positive lens L5, the fifth group has a sixth positive lens L6, and the sixth group has a seventh negative lens L7; wherein 4 and 5 defined by 4=f4/f and 5=f5/f by a composite focal length, f(>0) of the entire system for an e-line, a focal length, f4 of the fifth lens L5 for the e-line, a focal length, f5 of the sixth lens L6 for the e-line and Abbe numbers ν5 and ν6 of materials of the fifth lens L5 and the sixth lens, the Abbe numbers, ν5 and ν6 and the composite focal length, f satisfy a condition (1) of 0.0<4/ν5+5/ν6<0.04 and a condition (2) of 0.0<|f4-f5|/f<0.1.
ITO MASAHIRO
NISHINA KIICHIRO
| JP2000284172A | 2000-10-13 | |||
| JPS5627108A | 1981-03-16 | |||
| JPS34379B1 | ||||
| JPH05164961A | 1993-06-29 | |||
| JPS5746222A | 1982-03-16 | |||
| JPS5310425A | 1978-01-30 |
Toru Kabayama