US 11,988,895 B2
Observation optical system and apparatus having the same
Shuichi Mogi, Tochigi (JP)
Assigned to CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed by CANON KABUSHIKI KAISHA, Tokyo (JP)
Filed on Aug. 23, 2021, as Appl. No. 17/409,524.
Claims priority of application No. 2020-141265 (JP), filed on Aug. 24, 2020.
Prior Publication US 2022/0057600 A1, Feb. 24, 2022
Int. Cl. G02B 9/14 (2006.01); G02B 9/34 (2006.01); G02B 13/00 (2006.01); G02B 13/16 (2006.01); G02B 25/00 (2006.01)
CPC G02B 9/14 (2013.01) [G02B 9/34 (2013.01); G02B 13/0035 (2013.01); G02B 13/16 (2013.01); G02B 25/001 (2013.01)] 21 Claims
OG exemplary drawing
 
1. An observation optical system comprising, in order from a display panel side to an observation side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power; and
an optical path brancher configured to branch an optical path, and disposed between a display panel and the first lens,
wherein an absolute value of a radius of curvature of a lens surface on the observation side of the first lens is smaller than an absolute value of a radius of curvature of a lens surface on the display panel side of the first lens, and
wherein the following inequalities are satisfied:
0.5<d1/f<2.0
0.0<d23/d12<0.5
1.60311≤Ndg0<2.0000
1.768≤Ndg1<2.0
where d1 is a distance on an optical axis from a display plane of the display panel to the lens surface on the display panel side of the first lens when a diopter is −1 m−1, f is a focal length of the observation optical system, d23 is a distance on the optical axis from a lens surface on the observation side of the second lens to a lens surface on the display panel side of the third lens, d12 is a distance on the optical axis from the lens surface on the observation side of the first lens to a lens surface on the display panel side of the second lens, and Ndg0 is a refractive index of the optical path brancher for d-line, and Ndg1 is a refractive index of the first lens for d-line.