US 12,222,524 B2
Ocular optical system and head mounted display
Hidetsugu Takagi, Yokohama (JP); and Miho Matsumoto, Tokyo (JP)
Assigned to Nikon Corporation, Tokyo (JP)
Appl. No. 17/259,186
Filed by Nikon Corporation, Tokyo (JP)
PCT Filed Jun. 19, 2019, PCT No. PCT/JP2019/024219
§ 371(c)(1), (2) Date Jan. 10, 2021,
PCT Pub. No. WO2020/021916, PCT Pub. Date Jan. 30, 2020.
Claims priority of application No. 2018-138654 (JP), filed on Jul. 24, 2018.
Prior Publication US 2021/0157035 A1, May 27, 2021
Int. Cl. G02B 3/08 (2006.01)
CPC G02B 3/08 (2013.01) 12 Claims
OG exemplary drawing
 
1. An ocular optical system comprising:
a Fresnel lens including a plurality of Fresnel zones formed on a lens surface on an observation object side, wherein
the plurality of Fresnel zones are arranged concentrically side by side along an aspherical surface having a shape which is rotationally symmetric with respect to a central axis of the Fresnel lens, and satisfy the following conditional expression:
0<PAE1/PAC1≤0.50,
where
PAE1 represents an average pitch in a radial direction of Fresnel zones formed in a portion having a radius of 15 mm or more from the central axis of the Fresnel lens out of the plurality of Fresnel zones, and
PAC1 represents an average pitch in the radial direction of Fresnel zones formed in a portion having a radius of 15 mm or less from the central axis of the Fresnel lens excluding a first Fresnel zone located on a most central axis side of the Fresnel lens out of the plurality of Fresnel zones,
wherein
the aspherical surface is expressed by using the following expression:

OG Complex Work Unit Math
where
Zd represents a sag amount of the aspherical surface at a distance y from the central axis of the Fresnel lens,
Rd represents a radius of curvature of a reference spherical surface,
kd represents a conic constant, and
A2i represents a (2×i)-order aspherical coefficient, and
the following expression is satisfied:
kd≤−5.0.