Retrofocus wide-angle lens system and optical instrument provided with the same
View Patent ↗A retrofocus wide-angle lens system is provided, wherein the entire the wide-angle lens system is divided at a position that satisfies the following condition (1) between a theoretical front lens group having a negative refractive power, and a theoretical rear lens group having a positive refractive power including the diaphragm, at a minimum focal length, and wherein a flat parallel plate is disposed at the position that satisfies the following condition (1): 1.2<|fF/f|<4.0 . . . (1), wherein fF designates the focal length of the theoretical front lens group having a negative refractive power, and f designates the focal length of the entire the wide-angle lens system.
1. A retrofocus wide-angle lens system, wherein the entire said wide-angle lens system is divided at a position that satisfies the following condition (1) between a theoretical front lens group having a negative refractive power, and a theoretical rear lens group having a positive refractive power including the diaphragm, at a minimum focal length, and
wherein a flat parallel plate is disposed at said position that satisfies the following condition (1):
1.2<| fF/f|< 4.0 (1),
wherein
fF designates the focal length of said theoretical front lens group having a negative refractive power, and
f designates the focal length of the entire said wide-angle lens system.
2. The retrofocus wide-angle lens system according to claim 1 , wherein said wide-angle lens system comprises a wide-angle fixed focal-length lens system.
3. The retrofocus wide-angle lens system according to claim 1 , wherein said wide-angle lens system comprises a wide-angle zoom lens system.
4. The retrofocus wide-angle lens system according to claim 3 , wherein the position of said flat parallel plate remains at a fixed position on the optical axis during a zooming operation.
5. The retrofocus wide-angle lens system according to claim 1 , wherein said wide-angle lens system satisfies the following condition (2) at a minimum focal length:
0.1< d/f (2), wherein
d designates the thickness of said flat parallel plate, and
f designates the focal length of the entire said wide-angle lens system.
6. The retrofocus wide-angle lens system according to claim 1 , wherein said flat parallel plate comprises an optical filter.
7. The retrofocus wide-angle lens system according to claim 1 , wherein said flat parallel plate comprises a dummy glass plate.
8. An optical instrument provided with a retrofocus wide-angle lens system according to claim 1 .