An optical lens assembly includes, in order from a visual side to an image source side: a first lens with positive refractive power; an optical element including, in order from the visual side to the image source side, an absorptive polarizer, a reflective polarizer and a first phase retarder; a second lens with positive refractive power; a partial-reflective-partial-transmissive element; a second phase retarder; and an image source plane. The optical lens assembly has a total of two lenses with refractive power. A focal length of the optical lens assembly is f, a maximum image-source height of the optical lens assembly is IMH, a focal length of the first lens is f1, a focal length of the second lens is f2, and following conditions are satisfied: 0.40<IMH/f<1.26 and 0.21<f2/f1<2.35. A head-mounted electronic device includes the optical lens assembly.

An optical lens assembly includes, in order from a visual side to an image source side: a first lens with positive refractive power; an optical element including, in order from the visual side to the image source side, an absorptive polarizer, a reflective polarizer and a first phase retarder; a second lens with positive refractive power; a partial-reflective-partial-transmissive element; a second phase retarder; and an image source plane. The optical lens assembly has a total of two lenses with refractive power. A focal length of the optical lens assembly is f, a maximum image-source height of the optical lens assembly is IMH, a focal length of the first lens is f1, a focal length of the second lens is f2, and following conditions are satisfied: 0.40<IMH/f<1.26 and 0.21<f2/f1<2.35. A head-mounted electronic device includes the optical lens assembly.

The imaging lens consists of, in order from the object side, a front group that includes a stop and has a positive refractive power, and a rear group. During focusing, the entire front group integrally moves, and the rear group remains stationary with respect to an image plane. The rear group includes one or more air lenses formed by two concave lens surfaces facing toward each other. The imaging lens satisfies Conditional Expressions: 0.1<Bf/f<0.9 and −0.7<(Rrf+Rrr)/(Rrf−Rrr)<−0.025, where a back focal length of a whole system is Bf, a focal length of the whole system is f, and a curvature radius of an object side surface of the air lens in the rear group is Rrf and a curvature radius of an image side surface of the air lens in the rear group is Rrr.

The imaging lens consists of, in order from the object side, a front group that includes a stop and has a positive refractive power, and a rear group. During focusing, the entire front group integrally moves, and the rear group remains stationary with respect to an image plane. The rear group includes one or more air lenses formed by two concave lens surfaces facing toward each other. The imaging lens satisfies Conditional Expressions: 0.1<Bf/f<0.9 and −0.7<(Rrf+Rrr)/(Rrf−Rrr)<−0.025, where a back focal length of a whole system is Bf, a focal length of the whole system is f, and a curvature radius of an object side surface of the air lens in the rear group is Rrf and a curvature radius of an image side surface of the air lens in the rear group is Rrr.

An optical system and a projection device are provided. The optical system includes a display unit, a first lens group, a second lens group, and a reflector in sequence along a transmission direction of light; both the first lens group and the second lens group have positive focal powers; the optical system satisfies the following relationship: 0.01≤|φ.sub.100|≤0.02 and 0.005≤|.sub.φ200|≤0.015; φ.sub.100 represents a focal power of the first lens group, and φ.sub.200 represents a focal power of the second lens group.

An optical system and a projection device are provided. The optical system includes a display unit, a first lens group, a second lens group, and a reflector in sequence along a transmission direction of light; both the first lens group and the second lens group have positive focal powers; the optical system satisfies the following relationship: 0.01≤|φ.sub.100|≤0.02 and 0.005≤|.sub.φ200|≤0.015; φ.sub.100 represents a focal power of the first lens group, and φ.sub.200 represents a focal power of the second lens group.

An imaging lens system includes a first group having positive power and a second group having positive power disposed in that order from an object side to an image. The first group includes a first sub-group and a second sub-group. The second group includes a third sub-group, a stop, and a fourth sub-group. Conditional expressions (1), (2), and (3) below are satisfied:

0.07<f2/f1<0.4   (1);

0.45<f2/f2a<0.7   (2);

and

1.05<f/R1aN<1.55   (3)

where f denotes a focal length of an entirety of the imaging lens system focused at infinity, f1 denotes a focal length of the first group, f2 denotes a focal length of the second group focused at infinity, f2a denotes a focal length of the third sub-group focused at infinity, and R1aN denotes a radius of curvature of a surface closest to the image side within the first sub-group.

An imaging lens system includes a first group having positive power and a second group having positive power disposed in that order from an object side to an image. The first group includes a first sub-group and a second sub-group. The second group includes a third sub-group, a stop, and a fourth sub-group. Conditional expressions (1), (2), and (3) below are satisfied:

0.07<f2/f1<0.4   (1);

0.45<f2/f2a<0.7   (2);

and

1.05<f/R1aN<1.55   (3)

where f denotes a focal length of an entirety of the imaging lens system focused at infinity, f1 denotes a focal length of the first group, f2 denotes a focal length of the second group focused at infinity, f2a denotes a focal length of the third sub-group focused at infinity, and R1aN denotes a radius of curvature of a surface closest to the image side within the first sub-group.

An imaging device capable of a rotation in a predetermined direction includes a first lens unit having a first optical axis and a first focal length, a first imaging unit to image light passing through the first lens unit; a second lens unit having a second optical axis and a second focal length shorter than the first focal length, a second imaging unit to image light passing through the second lens unit, a dome shaped protection cover disposed on a subject side of the first and the second lens unit and protect the first and the second lens unit, and a support unit for supporting the first and the second lens unit so that an angle at which the first optical axis intersects an inner surface of the protection cover is closer to a vertical angle than an angle at which the second optical axis intersects the inner surface of the protection cover.

An imaging device capable of a rotation in a predetermined direction includes a first lens unit having a first optical axis and a first focal length, a first imaging unit to image light passing through the first lens unit; a second lens unit having a second optical axis and a second focal length shorter than the first focal length, a second imaging unit to image light passing through the second lens unit, a dome shaped protection cover disposed on a subject side of the first and the second lens unit and protect the first and the second lens unit, and a support unit for supporting the first and the second lens unit so that an angle at which the first optical axis intersects an inner surface of the protection cover is closer to a vertical angle than an angle at which the second optical axis intersects the inner surface of the protection cover.