A lens system (10) for image pickup includes, in order from an object side (11), a first lens group (G1) with positive refractive power that moves during focusing, a second lens group (G2) with positive refractive power that is disposed on an opposite side of a stop (St) to the first lens group and moves during focusing, and a third lens group (G3) with positive refractive power that is disposed closest to an image plane side (12) and is fixed. The third lens group includes, in order from the object side, a cemented lens (B31) composed of a lens with positive refractive power and a lens with negative refractive power. A combined focal length (f3) of the third lens group and a combined focal length (f12) of the first lens group and the second lens group satisfy a following condition: 2≤f3/f12≤200.

A lens system (10) for image pickup includes, in order from an object side (11), a first lens group (G1) with positive refractive power that moves during focusing, a second lens group (G2) with positive refractive power that is disposed on an opposite side of a stop (St) to the first lens group and moves during focusing, and a third lens group (G3) with positive refractive power that is disposed closest to an image plane side (12) and is fixed. The third lens group includes, in order from the object side, a cemented lens (B31) composed of a lens with positive refractive power and a lens with negative refractive power. A combined focal length (f3) of the third lens group and a combined focal length (f12) of the first lens group and the second lens group satisfy a following condition: 2≤f3/f12≤200.

An optical lens system includes, in order from the object side to the image side: a first lens with negative refractive power, a stop, a second lens with positive refractive power, and a third lens with positive refractive power, wherein a distance from an object-side surface of the first lens to an image-side surface of the third lens along an optical axis is TD, a distance from the image-side surface of the third lens to an image plane along the optical axis is BFL, half of a maximum view angle (field of view) of the optical lens system is HFOV, an incident pupil aperture of the optical lens system is EPD, and following conditions are satisfied: 1.82<TD/BFL<3.8 and 3.10<sin(HFOV)/EPD<8.12.

An image reading device includes a lens array including lenses arranged in a main scanning direction and forming an erect unmagnified optical system to converge light from a reading target, a holder holding the lens array, a light receiver to receive the light converged by the lenses, and slit units. Each slit unit includes three or more light shielding plates each separating an optical path of one lens from an optical path of another lens between the lens array and the light receiver, and side plates disposed on two sides of the light shielding plates in a direction intersecting the main scanning direction and connecting two adjacent light shielding plates. The slit units are arranged in the main scanning direction, and each two adjacent slit units are arranged with a space therebetween for one optical path of one lens.

An image reading device includes a lens array including lenses arranged in a main scanning direction and forming an erect unmagnified optical system to converge light from a reading target, a holder holding the lens array, a light receiver to receive the light converged by the lenses, and slit units. Each slit unit includes three or more light shielding plates each separating an optical path of one lens from an optical path of another lens between the lens array and the light receiver, and side plates disposed on two sides of the light shielding plates in a direction intersecting the main scanning direction and connecting two adjacent light shielding plates. The slit units are arranged in the main scanning direction, and each two adjacent slit units are arranged with a space therebetween for one optical path of one lens.

An electronic device comprises a display configured to display an image, an ocular optical system for viewing the display, and a control unit configured to control the display unit so as to change a display area of the display based on a distance from the ocular optical system to an eye of a user looking into the ocular optical system.

An electronic device comprises a display configured to display an image, an ocular optical system for viewing the display, and a control unit configured to control the display unit so as to change a display area of the display based on a distance from the ocular optical system to an eye of a user looking into the ocular optical system.

An optical projection device, which effectively suppresses variation in aberration due to irregularities in installation positions of lens groups which form an optical projection system, and a projector which includes the optical projection device are provided. In a lens group, which includes a diaphragm, in an optical projection device which includes a plurality of lens groups, a lens frame is divided between the diaphragm and a lens which is adjacent to the diaphragm, one lens frame which is acquired through the division includes an adjustment portion, which maintains a position of an optical axis to be adjusted, with respect to the other lens frame which is acquired through the division.

An optical projection device, which effectively suppresses variation in aberration due to irregularities in installation positions of lens groups which form an optical projection system, and a projector which includes the optical projection device are provided. In a lens group, which includes a diaphragm, in an optical projection device which includes a plurality of lens groups, a lens frame is divided between the diaphragm and a lens which is adjacent to the diaphragm, one lens frame which is acquired through the division includes an adjustment portion, which maintains a position of an optical axis to be adjusted, with respect to the other lens frame which is acquired through the division.

The objective optical system includes in order from an object side, a first unit having a positive refractive power, a second unit having a negative refractive power, and a third unit having a positive refractive power, and focusing is carried out by moving the second unit, the first unit and the third unit are fixed at the time of focusing, and the first unit G1 includes in order from the object side, a negative lens L1, one of a positive lens and a cemented lens, and a positive lens, and the third unit includes a positive lens, and a cemented lens of a positive lens and a negative lens, and the objective optical system satisfies the following conditional expression (3)
−20<f.sub.2/f<−5  (3) where, f.sub.2 denotes a focal length of the second unit, and f denotes a focal length of the overall objective optical system in a normal observation state.