US 11,860,510 B2
Observation device and image pickup apparatus including the same
Fumihiro Shinobu, Utsunomiya (JP)
Assigned to CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed by CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed on Dec. 1, 2022, as Appl. No. 18/060,662.
Application 18/060,662 is a continuation of application No. 16/697,253, filed on Nov. 27, 2019, granted, now 11,543,734.
Claims priority of application No. 2018-226995 (JP), filed on Dec. 4, 2018.
Prior Publication US 2023/0114678 A1, Apr. 13, 2023
Int. Cl. G03B 13/06 (2021.01); G02B 13/18 (2006.01); G02B 9/34 (2006.01); H04N 23/53 (2023.01)
CPC G03B 13/06 (2013.01) [G02B 9/34 (2013.01); G02B 13/18 (2013.01); H04N 23/53 (2023.01)] 5 Claims
OG exemplary drawing
 
1. An observation device, comprising:
an image display element that displays an image; and
a finder optical system that is used for observing the image displayed on an image display surface of 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 observation device 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;
−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.