US 9,810,885 B2
Imaging-optical system, stereo camera apparatus, and in-vehicle camera apparatus
Takahiro Nakayama, Kanagawa (JP); and Hiroshi Nakanuma, Kanagawa (JP)
Assigned to RICOH COMPANY, LTD., Tokyo (JP)
Filed by Takahiro Nakayama, Kanagawa (JP); and Hiroshi Nakanuma, Kanagawa (JP)
Filed on Feb. 25, 2015, as Appl. No. 14/631,216.
Claims priority of application No. 2014-042619 (JP), filed on Mar. 5, 2014.
Prior Publication US 2015/0253548 A1, Sep. 10, 2015
Int. Cl. G02B 13/04 (2006.01)
CPC G02B 13/04 (2013.01) 20 Claims
OG exemplary drawing
 
1. A retro-focus type imaging-optical system comprising, in order from an object side to an image side:
a first lens group;
an aperture stop; and
a second lens group, wherein
the first lens group includes, in order from the object side, a positive first F lens group and a negative first R lens group,
the first F lens group consists of a positive meniscus lens having a convex surface on the object side,
the first R lens group consists of a negative meniscus lens having a convex surface on the object side and a positive lens,
the second lens group includes, in order from the object side, a positive second F lens group and a second R lens group,
the second F lens group includes a positive meniscus lens having a convex surface on the image side, and
an air gap is provided between the negative meniscus lens having the convex surface on the object side and the positive lens of the first R group in the first lens group such that there is no intervening lens therebetween said air gap being a largest air gap in the imaging-optical system.