Patent ID: 11927723
Assignee: CANON KABUSHIKI KAISHA
Field: Optics (Instruments)
Classification: CPC G  B | IPC B  G

Claim 0:
1. An optical system comprising a front lens unit having a positive or negative refractive power, a diaphragm, and a rear lens unit having a positive refractive power, which are arranged in this order from an object side to an image side,
wherein the front lens unit includes an aspherical lens that has a positive refractive power on an optical axis, and is disposed closest to an object,
wherein the aspherical lens has an aspherical surface on the object side in which an off-axis radius of curvature is larger than an on-axis radius of curvature, and
wherein the following conditional expressions are satisfied:

0.45≤D1s/L≤0.65

2.6≤Dr8/Dr4≤30.0, where D1s is a distance on the optical axis from the aspherical surface to the diaphragm, L is an overall optical length of the optical system, and Dr4 and Dr8 are sag amounts from a reference spherical surface at positions of 40% and 80% of an effective diameter of the aspherical surface, respectively, the reference spherical surface being a spherical surface passing through a point of the aspherical surface on the optical axis and a point of the aspherical surface at a position of the effective diameter.