Patent ID: 11860510
Assignee: CANON KABUSHIKI KAISHA
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  H | IPC G  H

Claim 4:
5. An image pickup apparatus, comprising:
an image pickup element;
an image display element that displays an image obtained by the image pickup element; and
a finder optical system that is used for observing the image displayed on the image display element, wherein
the finder optical system includes a first lens with a positive refractive power, a second lens with a negative refractive power, a third lens with a positive refractive power, and a fourth lens with a positive refractive power arranged in this order from an image display surface side to an observation side, wherein the image pickup apparatus further comprises a cover glass arranged at the image display surface side of the first lens,
wherein an air interval on an optical axis between the cover glass and the image display surface is larger than an air interval on the optical axis between the cover glass and the first lens,
wherein the fourth lens does not move during a diopter adjustment, and wherein
the following conditional expressions are satisfied:

−0.70<f2/f<−0.20;

0.7<(R22+R21)/(R22−R21)≤1.361;

0.31<H/f<0.50; and

−8.5<(R21+R12)/(R21−R12)<−2.0

0.619≤f3/f1<3.10; and

−0.482≤(R31−R22)/(R31+R22)≤0.223,, where f2 is a focal length of the second lens, f is a focal length of the finder optical system, R21 is a curvature radius of a lens surface of the second lens on the image display surface side, R22 is a curvature radius of a lens surface of the second lens on the observation side, H is a half of a diagonal length of the image display surface, R12 is a curvature radius of a lens surface of the first lens on the observation side, f1 is a focal length of the first lens, f3 is a focal length of the third lens, and R31 is a curvature radius of a lens surface of the third lens on the image display surface side.