77results about How to "Back focal length" patented technology

There is provided an image pickup lens having a 6-element structure which has a small size and a sufficiently lens speed of F/2 or less and in which various aberrations are corrected favorably. This image pickup lens includes a first lens having a positive refractive power and comprising a convex surface directed to the object side; a second lens having a negative refractive power and comprising a concave surface directed to the image side; a third lens having a positive or negative refractive power; a fourth lens having a positive refractive power; a fifth lens having a positive refractive power and comprising a convex surface directed to the image side; and a sixth lens having a negative refractive power and comprising a concave surface directed to the image side, in this order from the object side, wherein the image side surface of the sixth lens has an aspherical shape and an inflection point at a position other than an intersection point with the optical axis, and the image pickup lens satisfies the following conditional expressions.

ν1>50

ν2≦30

where,

• • ν1 is an Abbe number of the first lens, and
  • ν2 is an Abbe number of the second lens.

In an objective lens for an endoscope, the full angle of view exceeds 120 degrees, and a most-object-side surface of the objective lens is spherical. Further, the following condition formulas (1) and (2) are satisfied:

0.7<θ8/θ10<0.8  (1); and

5<R₁/f<15  (2),

• • where θ10: half angle of view corresponding to a maximum image height;
  • θ8: half angle of view corresponding to an image height that is 80% of the maximum image height;
  • R₁: curvature radius of the most-object-side surface; and
  • f: focal length of the entire system of the objective lens.

An image pickup lens having a four lens configuration in which a bi-concave first lens, a bi-convex second lens, a bi-concave third lens, and a positive fourth lens are disposed in this order from an object side. Here, at least one of the first, second, third, and fourth lenses has an aspherical surface on each side. The image pickup lens satisfies Conditional Expression (1) given below when a refractive index of the second lens with respect to d-line is taken as Nd2.

1.6<Nd2  (1)

A far-infrared camera includes three lenses formed of ZnS. A first lens is a biconvex lens, a second lens is a negative meniscus or biconcave lens, and a third lens is a positive meniscus lens. A diffraction surface is formed in either surface of a lens. When a total focal distance f of the lens system is 10 mm to 30 mm and a focal distance f₁₂ of the first and second lenses is 20 mm to 70 mm, 1≦f₁₂/f≦3.

To allow placement of optical members by providing a long back focus, make aberrations less subject to manufacturing errors, and reduce variations in aberrations during focusing. An endoscopic objective optical system includes, in order from an object side, a front group with negative refractive power, a focusing lens, and a rear group with positive refractive power, wherein: the endoscopic objective optical system satisfies conditional expressions (1) to (4) below:

4<FB/FL  (1)

FL/|Fc|<0.1  (2)

−3<F_—F/FL<−0.9  (3)

2.5<F_—R/FL<5  (4)

• • where FB is back focus of the entire system, FL is a focal length of the entire system, fc is a focal length of the focusing lens, |fc| is an absolute value of fc, F_F is a focal length of the front group, and F_R is a focal length of the rear group.

A zoom lens includes, in order from an enlargement side to a reduction side, a first lens unit having a positive refractive power, which is stationary for variation of magnification, a second lens unit having a negative refractive power, which moves for variation of magnification, a third lens unit having a negative refractive power, which moves for variation of magnification, a fourth lens unit having a positive refractive power, which includes a stop and which moves for variation of magnification, and at least one lens unit. In the zoom lens, for variation of magnification from a wide-angle end to a telephoto end, the second lens unit and the third lens unit move towards the reduction side and the fourth lens unit move towards the enlargement side. The zoom lens satisfies an appropriate condition.

A variable-magnification projection optical system substantially consists of a negative first lens group that is disposed at the most enlargement-side position and is fixed during magnification change, a positive last lens group that is disposed at the most reduction-side position and is fixed during magnification change, and a plurality of lens groups that are disposed between the first lens group and last lens group and are moved during magnification change. The most enlargement-side lens group (the second lens group) of the lens groups that are moved during magnification change has a negative refractive power. Predetermined conditional expressions relating to a back focus of the entire system on the reduction side at the wide-angle end, a focal length of the entire system at the wide-angle end, a focal length of the second lens group and a focal length of the last lens group are satisfied.

A zoom lens with a reduced overall length having a color separating prism therein and a telecentric property with a first lens group (GI) having a positive refractive power and having a fixed position, a second lens group (GII) of the variable magnification type having a negative refractive power and having a position movable for magnification variation, a third lens group (GIII) having a positive refractive power and having a fixed position and a fourth lens group (GIV) having a positive refractive power and having a position variable for adjustment of a focal position upon magnification variation and upon focusing are disposed in order from an object side. At least one face of the two convex lenses in the fourth lens group is formed from an aspheric face.

A zoom lens for projection includes negative first group G₁, positive second group G₂, positive third group G₃, negative fourth group G₄, positive fifth group G₅, and positive sixth group G₆, arranged from the magnification side of the zoom lens. The reduction side of the zoom lens is telecentric. When the magnification is changed, the first group G₁ and the sixth group G₆ are fixed, and the second through fifth groups G₂ through G₅ move. The fourth group G₄ is a negative lens having a concave surface facing the magnification side, and the fifth group G₅ includes at least two positive lenses and at least two negative lenses. Further, the following formula (1) is satisfied:

−5.0≦f4/fw≦−1.2  (1),

• • where f4: the focal length of the fourth group; and
  • fw: the focal length of the entire system of the zoom lens at a wide angle end.

A projection zoom lens having broad angle of view, high zoom ratio, and large back focus while aberrations are corrected satisfactorily, including a negative first lens group, a positive second lens group, a positive third lens group, a negative fourth lens group, a positive fifth lens group, and a positive sixth lens group from the magnification side and is telecentric on the reduction side. When zooming, the first and sixth lens groups are fixed while the second to fifth lens groups are moved and the fourth lens group is composed of one negative lens whose magnification side surface has a greater curvature in absolute value than that of the reduction side surface, and the zoom lens satisfies conditional expression (1): −12.0<f4/fw<−5.0, where f4 is focal length of the fourth lens group, and fw is focal length of the entire lens system at the wide angle end.

A variable-magnification projection optical system substantially consists of a negative first lens group that is disposed at the most enlargement-side position and is fixed during magnification change, a positive last lens group that is disposed at the most reduction-side position and is fixed during magnification change, and a plurality of lens groups that are disposed between the first lens group and last lens group and are moved during magnification change. The lens groups that are moved during magnification change substantially consist of three lens groups, wherein the most enlargement-side lens group is a negative lens group. Predetermined conditional expressions relating to a back focus of the entire system on the reduction side at the wide-angle end, a focal length of the entire system at the wide-angle end, a focal length of the last lens group, and a focal length of the first lens group are satisfied.

The present invention provides a zoom lens that suppresses the generation of unnecessary light and is suitable for a projection lens. The zoom lens is used as a projection lens of a projector in which a prism is located between the projection lens and a spatial optical modulating element B. A lens closest to the spatial optical modulating element B is a meniscus positive lens whose convex surface faces a screen. A refractive index of the meniscus positive lens is 1.75 or more.

A variable magnification projection optical system substantially consisting of two lens groups of a first lens group having a positive refractive power and is moved during magnification change, and a second lens group having a positive refractive power and is moved during magnification change, in which the variable magnification projection optical system is configured such that the reduction side is telecentric.

An inexpensive projection lens unit in a rear projection type image display system, having a short focal distance (wide angle of viewing field), high focus and high contrast, and as well, including a power lens made of a glass material having a high refractive index in a range from 1.63 to 1.70 and an Abbe's number of not less than 50 with an optimized incident and emergent configuration in order to satisfactorily correct aberration with a enhanced focusing performance even with a shortened focal distance. Further, the power lens having a high refractive index can exhibit a high power, and accordingly, can carry out satisfactory aberration correction by optimizing the aspheric degree of a plastic lens even though the length of back focus is increased for enhancing the contrast.