JP2984956B2 - Shooting lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographic lens, and more particularly to a lens system of a pre-aperture type used mainly for a video camera and a still video camera.

[0002]

2. Description of the Related Art In general, in a video camera and a still video camera, a low-pass filter for cutting high-frequency components of light and an optical member of a color separation system are often arranged between a lens system and an image pickup device. The lens system needs a long back focus in order to secure the space of. Further, when a stripe filter or a mosaic filter is disposed as a color separation system in front of the image sensor, the telecentricity is improved, and a principal ray of a light beam emitted from the final surface of the lens system and incident on the filter, and a lens. It is important that the angle formed by the system with the optical axis be as small as possible without depending on the image height in order to prevent color bleeding.

[0003] From the object side, positive, negative, negative and positive junction, positive 4
A photographic lens system composed of five lenses in a group and having a long back focus is disclosed in, for example, JP-A-63-75718, JP-A-54-48232, and JP-B-60-34.
724 and the like. However, JP-A-63-75
No. 718 describes that the shooting angle of view (2ω) is 38 °.
The degree is narrower than that of the present invention, and the present invention has a different application. Further, those described in JP-A-54-48232 and those described in JP-B-60-34724 are F2.5 and F2.8, which are slightly darker than those of the present invention, respectively. It was developed as a camera lens for silver halide photography, and if it is used for a video camera or a still video camera with a small screen size, the edge thickness of the lens and the axial core thickness become thin, which causes processing problems. Occurs.

[0004]

The present invention has an F number of 2, an imaging angle of view (2ω) of about 50 °, a sufficiently long back focus, and a difference between the principal ray of each emitted light beam and the optical axis. An object of the present invention is to realize a lens system with a small angle and good aberration correction.

[0005]

Means for Solving the Problems To achieve the above object,
Therefore, the photographic lens of the present invention includes a first lens in order from the object side.
Lens group is a positive single lens, the second lens group is a biconcave single lens,
The third lens group consists of a negative lens and a positive lens cemented together.
The skas lens and the fourth lens group are 5 elements in 4 groups of positive single lens
And satisfying the following condition. _{(1) 2.35 <f 1 ·} 2 / f <3.6 However f: the focal point of the entire system length f _{1 · 2:} a composite focal length of the first lens group and the second lens group. Further, the first lens group of the photographing lens is
It is a convex single lens, and an aperture is provided in front of the first lens group.
Lens that meets the following conditions:
Is desirable. _{(2) n 1> 1.75 (} 3) ν 4 -ν 3> 10 (4) 0.75 <r 1 / f <2.05 (5) -0.85 <r 3 / f <-0. 45 (6) 0.45 <r ₄ /f<1.20, where n ₁ : refractive index ν ₃ of the first lens group : Abbe number ν ₄ of the negative lens of the third lens group: positive lens of the third lens group Abbe number r _1: the first lens group on the object side surface of the radius of curvature r _3: the second lens group on the object side surface of the radius of curvature r _4: is a radius of curvature of the object side surface of the second lens group .

[0006]

In the lens system according to the present invention, a sufficient back focus is obtained by disposing the negative lens as the second lens group relatively closer to the object side and the third lens group as a meniscus lens having a concave surface facing the object side. In addition, spherical aberration is satisfactorily corrected by making the third lens group a cemented lens of a negative lens and a positive lens. Further, by disposing the stop in front of the first lens group, the distance from the image plane to the exit pupil can be increased, and as a result, the principal ray and light of each light beam emitted from the final surface of the lens system. The angle formed with the axis becomes small, which is suitable for a video camera or a still video camera. At the same time, the lenses can be dropped into the lens frame at the time of manufacture, which leads to cost reduction.

Hereinafter, each conditional expression will be described. Conditional expression (1) satisfies the basic problem of the lens of the present invention of securing a sufficient back focus and favorably corrects distortion. When the combined focal length of the first lens unit and the second lens unit exceeds the upper limit, the positive refractive power must be increased in the rear lens unit, and the negative distortion increases. Conversely, if the lower limit is exceeded, sufficient back focus cannot be secured.

The conditional expression (2) is mainly for favorably correcting spherical aberration. If the lower limit of this expression is exceeded, the spherical aberration will be undercorrected.

Conditional expression (3) is for correcting chromatic aberration, in particular, chromatic aberration of magnification.
The g-line image becomes smaller than the line.

Conditional expression (4) is provided for favorably correcting spherical aberration. If the curvature of the object side surface of the first lens unit becomes tighter than the lower limit of this expression, the second lens as a negative lens because ray height is low in the group, negative spherical aberration of higher order generated by this surface r ₁ is not completely corrected. On the other hand, when the curvature is reduced beyond the upper limit, the spherical aberration is overcorrected.

Conditional expression (5) is a condition for correcting the spherical aberration generated in the first lens group. When the curvature of the object side surface of the second lens group becomes lower than the lower limit, the spherical aberration is corrected. Insufficient, and conversely, exceeding the upper limit results in overcorrection.

Conditional expression (6) is for favorably correcting astigmatism. If the curvature of the image-side surface of the second lens group is loosened beyond the upper limit, the meridional image plane falls under, and conversely, if the curvature exceeds the lower limit and becomes tight, the meridian image plane becomes over.

[0013]

Next, an embodiment of the taking lens according to the present invention will be described. Where f is the focal length of the entire system, r is the radius of curvature of each lens surface,
d is the lens thickness or lens interval, nd is the refractive index, and νd is the Abbe number. In addition, a cover glass is mounted on the image side of the lens system, and both are shown.

Embodiment 1 f = 9.10 2ω = 50 ° 24 'F-number =
2.03 _{. r 1 /f=1.17 r 3 /f=-0.63 r} 4 /f=0.71 f 1 2 /f=2.62 distance from image plane to the exit pupil: + 206.5mm (binding The exit pupil is in the opposite direction to the object when viewed from the image plane.) The stop is located 1.5 mm from the first surface to the object side.

Embodiment 2 f = 9.09 2ω = 50 ° 26 ′ F-number =
2.03 _{. r 1 /f=1.15 r 3 /f=-0.61 r} 4 /f=0.72 f 1 2 /f=3.38 distance from image plane to the exit pupil: + 389.6mm (binding The exit pupil is in the opposite direction to the object when viewed from the image plane.) The stop is located 1.5 mm from the first surface to the object side.

Embodiment 3 f = 9.09 2ω = 49.58 ′ F-number =
2.03 _{. r 1 /f=1.05 r 3 /f=-0.60 r} 4 /f=0.78 f 1 2 /f=3.07 distance from image plane to the exit pupil: 238.2mm (binding The exit pupil is in the opposite direction to the object when viewed from the image plane.) The stop is located 1.5 mm from the first surface to the object side.

Embodiment 4 f = 9.10 2ω = 50 ° 21 ′ F-number =
2.03 _{. r 1 /f=1.95 r 3 /f=-0.55 r} 4 /f=1.16 f 1 2 /f=2.85 distance from image plane to the exit pupil: 238.2mm (binding The exit pupil is in the opposite direction to the object when viewed from the image plane.) The stop is 1.75 mm from the first surface to the object side.

Example 5 f = 9.09 2ω = 49 ° 55 ′ F-number =
2.03 _{. r 1 /f=0.91 r 3 /f=-0.65 r} 4 /f=0.58 f 1 2 /f=2.47 distance from image plane to the exit pupil: 360.0mm (binding The exit pupil is in the opposite direction to the object when viewed from the image plane.) The stop is located 1.5 mm from the first surface to the object side.

[0019]

As is clear from the examples and the aberration diagrams, the present invention is as bright as about F2, has an angle of view of 50 °, has telecentricity, and has sufficient back focus and lens thickness. In addition, a photographing lens suitable as a lens for a video camera or a still video camera is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a photographic lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a photographic lens according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a photographic lens according to a third embodiment of the present invention;

FIG. 4 is a sectional view of a photographic lens according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a photographic lens according to a fifth embodiment of the present invention.

FIG. 6 is an aberration curve diagram of Example 1 of the photographing lens of the present invention.

FIG. 7 is an aberration curve diagram of Example 2 of the photographing lens of the present invention.

FIG. 8 is an aberration curve diagram of Example 3 of the taking lens of the present invention.

FIG. 9 is an aberration curve diagram of Example 4 of the taking lens of the present invention.

FIG. 10 is an aberration curve diagram of Example 5 of the taking lens of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (2)

(57) [Claims] 1. A first lens unit includes, in order from an object side, a positive single
Lens, 2nd lens group is a biconcave single lens, 3rd lens group
Is a meniscus lens formed by joining a negative lens and a positive lens
And the fourth lens group is composed of five positive lens elements in four groups.
Is a photographic lens 2.35 and satisfies the following condition _{<f 1 · 2 / f <} 3.6 However f: the focal point of the entire system length f _{1 · 2:} first lens group and the second lens This is the composite focal length of the group . 2. The photographing lens according to claim 1, wherein the first lens group has two lenses.
It is a convex single lens, and an aperture is provided in front of the first lens group.
Lens that meets the following conditions:
2. The photographing lens according to claim 1, wherein: n ₁  > 1.75 ν ₄ −ν ₃  > 10 0.75 <r ₁ /F<2.05 -0.85 <r ₃ /F<-0.45 0.45 <r ₄ /F<1.20  Where n ₁ : Refractive index of the first lens group ν ₃ : Abbe number of the negative lens in the third lens group ν ₄ : Abbe number of the positive lens in the third lens group r ₁ : Radius of curvature of the object-side surface of the first lens group r ₃ : Radius of curvature of the object-side surface of the second lens group r ₄ : Radius of curvature of the object-side surface of the second lens group It is.