Patent ID: 11880022
Assignee: PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  H  B | IPC B  G  H

Claim 11:
12. A lens system that forms an image on an imaging element, comprising:
a first lens element, a second lens element, and a third lens element, which are arranged in order from an object side to an image surface side along an optical axis; a diaphragm arranged closer to the image surface side than the third lens element and a lens element on the image surface side, which is arranged closer to the image surface side than the diaphragm,
wherein
at least one of the first lens element and the second lens element has a free-curved surface that is rotational asymmetric with respect to the optical axis, and one of the first lens element and the second lens element has free-curved surfaces on both sides of the object side and the image surface side,
the third lens element has free-curved surfaces that are rotational asymmetric with respect to the optical axis, on both sides of the object side and the image surface side,
the first lens element has a shape of a surface facing the object side, the shape being convex toward the object side,
the second lens element has a shape of a surface facing the image surface side, the shape being convex toward the object side,
the third lens element has a shape of a surface facing the object side, the shape being convex toward the image surface side,
the lens element on the image surface side has, at least on the object side, a free-curved surface that is rotational asymmetric with respect to the optical axis, and
the lens system satisfies a following conditional expression (7):

|ΔNdF/ΔNd1|  (7), where,
ΔNd1 is a refractive index change rate of the first lens element with respect to d-line in response to a temperature change at 25° C., and
ΔNdF is a refractive index change rate of a lens element having the free-curved surface with respect to d-line in response to a temperature change at 25° C.