The present invention provides a camera optical lens, including, from an object side to an image side, a first lens having a positive refractive power, a second lens a negative refractive power, a third lens having a positive refractive power, a fourth lens having a negative refractive power, and a fifth lens. At least one of the first lens to the fifth lens has a free-form surface, and the camera optical lens satisfies 0.50≤f3/f≤1.20; and 1.50≤R7/R8, where f denotes a focal length of the camera optical lens, f3 denotes a focal length of the third lens, R7 is a central curvature radius of an object side surface of the fourth lens, and R8 is a central curvature radius of an image side surface of the fourth lens. The camera optical lens has excellent optical performance while meeting requirements of a long focal length and ultra-thinness.

A camera optical lens includes five-piece lenses, from an object side to an image side. The camera optical lens satisfies conditions of 0.65≤f1/f≤0.85, 1.20≤(R7+R8)/(R7−R8)≤1.75, −40.00≤f3/f≤−20.00, 0.50≤d5/d6≤0.80 and 1.00≤d8/d9≤1.30. Here f denotes a focal length of the camera optical lens, f1 denotes a focal length of the first lens, f3 denotes a focal length of the third lens, R7 denotes a curvature radius of an object-side surface of the fourth lens, R8 denotes a curvature radius of an image-side surface of the fourth lens, d5 denotes an on-axis thickness of the third lens, d6 denotes an on-axis distance from an image-side surface of the third lens to the object-side surface of the fourth lens. The camera optical lens of the present disclosure has excellent optical performances, and meanwhile can meet design requirements of a large aperture, a wide angle and ultra-thin.

An imaging lens consisting of, in order from an object side to an image side: a front group; a stop; and a rear group that has a positive refractive power. The imaging lens satisfies predetermined conditional expressions.

An imaging lens consisting of, in order from an object side to an image side: a front group; a stop; and a rear group that has a positive refractive power. The imaging lens satisfies predetermined conditional expressions.

A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

There is provided a highly efficient virtual image projection device in a small size that displays images of high luminance in which an illumination system is reduced in size with no degradation in an effective luminous light beam. A virtual image projection device that shows video to a human eye includes a virtual light source surface (116) that emits a light beam in a predetermined angular distribution, an image forming lens (117) that condenses the light beam from the virtual light source surface (116), and a display (120) that creates video. When the virtual light source surface (116) is disposed at a nearly focal position on the front side of the image forming lens (117), the display (120) is disposed at a nearly focal position on the rear side of the image forming lens.

There is provided a highly efficient virtual image projection device in a small size that displays images of high luminance in which an illumination system is reduced in size with no degradation in an effective luminous light beam. A virtual image projection device that shows video to a human eye includes a virtual light source surface (116) that emits a light beam in a predetermined angular distribution, an image forming lens (117) that condenses the light beam from the virtual light source surface (116), and a display (120) that creates video. When the virtual light source surface (116) is disposed at a nearly focal position on the front side of the image forming lens (117), the display (120) is disposed at a nearly focal position on the rear side of the image forming lens.

The present invention provides an optical imaging lens. The optical imaging lens comprises six lens elements positioned in an order from an object side to an image side. Through controlling convex or concave shape of surfaces of the lens elements and designing parameters satisfying at least one inequality, the optical imaging lens may present a great angle of view with smaller surface area of the front side of the optical imaging lens.

An observation device according to the present invention includes an image display element displaying an image, and a finder optical system used for observing the image displayed on an image display surface of the image display element. The finder optical system includes a positive first lens, a negative second lens, and a biconvex positive third lens arranged in this order from the image display surface side to the observation side. A focal length of the second lens, a focal length of the finder optical system, a curvature radius of a lens surface of the second lens on the image display surface side, a curvature radius of a lens surface of the second lens on the observation side, a diagonal length of the image display surface, and a curvature radius of a lens surface of the third lens on the image display surface side are appropriately set.