JPH07113951A - Retro-focus type wide angle lens - Google Patents

Abstract

PURPOSE:To provide a retro-focus type wide angle lens having a long back- focus, the high optical performance over a whole screen and an F-number of about 1.6. CONSTITUTION:From the object side in order, this lens is composed of nine groups ten lenses of a first positive lens whose convex surface of an intense refractive power confronts the objective side, a second negative meniscus lens whose convex surface confronts the object side, a third positive lens whose convex surface of intense refractive power confront the image side IP, a fourth negative lens having both concave lens surfaces, a fifth positive lens whose both lens surfaces are convex surfaces, a diaphragm, a combined lens joining a sixth negative meniscus lens to a seventh positive lens whose both lens surfaces are convex surfaces, a eighth negative lens whose both lens surfaces are concave surfaces, a ninth positive lens whose both lens surfaces are convex surfaces and a tenth positive lens whose convex surface of intense refractive power confronts the object side and both lens surfaces are convex surfaces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a photographing angle of view of about 70 degrees, F
The present invention relates to a retro-focus wide-angle lens with a number of about 1.6, and particularly to a large-aperture ratio retro-focus wide-angle lens having a long back focus suitable for a small image pickup camera and the like, and having high optical performance over the entire screen. is there.

[0002]

2. Description of the Related Art Conventionally, a so-called retrofocus type wide-angle lens in which a lens group having a negative refractive power precedes is well known as a wide-angle wide-angle lens having a back focus longer than a focal length.

For example, Japanese Laid-Open Patent Publication No. Sho 49-121527 proposes a retrofocus wide-angle lens having a long back focus with a photographing field angle of 100 degrees and an F number of about 3.5.

In recent years, a handy type ultra-miniature television camera has come to be used as one of image pickup devices, from an image pickup tube (tube) to a solid-state image pickup device such as a CCD as the image pickup means is downsized. . It is desired that the photographic lens used for them has a bright F number, good telecentric characteristics, and good imaging performance. Further, as a lens system used for a television camera, an optical member such as a low-pass filter or a color filter is arranged between a taking lens and an image pickup surface, and thus it is necessary to have a long back focus.

[0005]

Generally, a retrofocus type wide-angle lens has an asymmetric lens structure in which a lens unit having a negative refractive power is arranged in the front and a lens unit having a positive refractive power is arranged in the rear.

Therefore, the amount of various aberrations such as spherical aberration, coma aberration, distortion aberration, and astigmatism increases, and the absolute value of the negative refractive power of the front lens group is increased in order to secure a long back focus. Therefore, the amount of various aberrations is further increased, and it is generally difficult to correct these aberrations in a well-balanced manner.

In particular, in a retrofocus wide-angle lens, when it is attempted to secure a sufficiently long back focus, there are drawbacks such that the total lens length becomes long and the front lens diameter becomes large.

The present invention has a long back focus to the extent that various optical members such as filters can be arranged between the taking lens and the image pickup surface by appropriately setting the lens configuration, and the front lens diameter is reduced. The shooting angle of view is about 70 degrees, and the F number is 1.
It is an object of the present invention to provide a retrofocus wide-angle lens having high optical performance in which various aberrations of the entire screen are well corrected with a wide angle of view of about 6.

[0009]

A retrofocus type wide-angle lens according to the present invention comprises, in order from the object side, a positive first lens having a convex surface having a strong refractive power facing the object side, and a meniscus lens having a convex surface facing the object side. Negative second lens, a positive third lens with a convex surface having a strong refractive power facing the image side, a negative fourth lens with both lens surfaces concave, a fifth positive lens with both lens surfaces convex,
A diaphragm, a cemented lens in which a negative meniscus sixth lens having a convex surface facing the object side and a positive seventh lens having both lens surfaces are cemented, a negative eighth lens having both concave lens surfaces, A positive ninth lens having a convex lens surface, and a positive tenth lens having a convex surface having a strong refractive power facing the object side and having a convex surface.
It is characterized by being composed of 10 lenses in 9 groups.

[0010]

EXAMPLE 1 FIG. 1 is a lens sectional view of Numerical Example 1 of the present invention described later.

In the figure, L1 is the first group (front group) having negative refractive power,
L2 is a second group (rear group) having a positive refractive power, SP is an aperture, and IP
Is the image plane.

G is an optical member such as a low-pass filter or a color filter.

According to the present invention, by appropriately setting the lens shapes of the five lenses forming the first lens unit L1 having a negative refractive power and the five lenses forming the second lens unit having a positive refractive power, as described above. , While maintaining good optical performance of the entire screen, has a back focus of a predetermined length, and the entire lens system is a good teleselective system,
In particular, the exit pupil and the back focus of the entire lens system are lengthened, and spherical aberration, coma, etc. are well corrected.

Specifically, the first lens is a positive lens having a convex surface having a strong refractive power facing the object side, the second lens is a meniscus negative lens having a convex surface facing the object side, and the third lens is facing the image surface side. As a positive lens having a convex surface having a strong refractive power, this gradually refracts a light beam with a large incident angle in the vicinity of a shooting field angle of 70 degrees to reduce the angle formed with the optical axis.

Thus, the diameter of the front lens is reduced while minimizing the occurrence of various aberrations such as distortion, astigmatism, and high-order aberration.

In the above description, the lens surface having a strong refractive power on the object side has a smaller radius of curvature than the other lens surface, that is, the lens surface on the image side. The same applies to a lens surface having a strong refractive power on the image plane side.

The fourth lens is a negative lens whose concave surfaces are both lenses, and mainly corrects the spherical aberration. By making the ninth lens a positive lens whose both lens surfaces are convex, spherical aberration, coma and astigmatism are well corrected.

A cemented lens in which a negative meniscus sixth lens having a convex surface facing the object side of the second lens unit having a positive refractive power and a positive seventh lens having convex lens surfaces on both surfaces are cemented,
Fourth group 5 of the negative eighth lens having both concave lens surfaces, the positive ninth lens having both convex lens surfaces, and the tenth positive lens having both convex convex lenses facing the object side By configuring it with one sheet, various aberrations of the entire screen are corrected in a well-balanced manner.

Further, the light returning from the image pickup surface IP is reflected again by each lens surface of the sixth lens to the tenth lens, and all the ghost light returning to the image surface is imaged on the object side from the image surface. This effectively prevents the generation of strong ghost light.

The retrofocus wide-angle lens of the present invention achieves high optical performance by forming the lens shape of each lens group as described above. To further improve the performance of the entire screen, It is good to satisfy the conditions of.

(1-1) When the curvature radii of the object side lens and the image side lens of the fourth lens are R ₄₁ and R ₄₂ respectively, 0.7 <| R ₄₁ / R ₄₂ | <1.2 ( 1) To satisfy the following conditional expression.

Conditional expression (1) mainly effectively corrects spherical aberration by making the radiuses of curvature of the object side and image side lens surfaces of the fourth lens substantially the same. In other words, the lens surfaces on the object side and the image surface side are balanced by performing the reverse aberration correction.

The radius of curvature R exceeds the upper limit of conditional expression (1).
_{If 42} is too small, the spherical aberration is under, and conversely, if the radius of curvature R ₄₁ is too small beyond the lower limit, the spherical aberration is too large, which is not good.

(1-2) When radiuses of curvature of the object-side and image-side lens surfaces of the ninth lens are R ₉₁ and R ₉₂ , respectively, 0.9 <| R ₉₁ / R ₉₂ | <1.4 (2) It is to satisfy the following condition.

Conditional expression (2) is similar to conditional expression (1) in that the radiuses of curvature of the object-side and image-side lens surfaces of the ninth lens have substantially the same curvature, and is mainly used by the eighth lens. The generated spherical aberration, coma and astigmatism are well corrected. If the radius of curvature R ₉₂ becomes too small beyond the upper limit, spherical aberration will become under. If the radius of curvature R ₉₁ is too small below the lower limit, coma and astigmatism will be excessive, which is not preferable.

(1-3) In the present embodiment, focusing is performed by so-called total extension of the entire lens, and a rear focus method of moving a lens (sixth to tenth lens) on the image plane side of the diaphragm SP is used. May be.

Further, in order to maintain good optical performance in the super close range, the first group L1 of the lenses (first to fifth lenses) on the object side of the aperture stop SP and the lens (first lens on the image plane side of the aperture stop SP). A so-called floating method of separately moving the second group L2 of the sixth to tenth lenses) may be used. At this time the first
When the moving amount of the group is MF and the moving amount of the second group is MR, it is preferable in terms of aberration correction that the focusing is performed by moving so as to have a relationship of 0.4 <MF / MR <0.7 (3).

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number.

In the numerical examples, the last two lens surfaces are glass blocks such as face plates and filters.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical Example 1 F = 6.20 fno = 1: 1.65 2ω = 68.2 ° R 1 = 18.59 D 1 = 3.00 N 1 = 1.60342 ν 1 = 38.0 R 2 = -2564.93 D 2 = 0.15 R 3 = 12.69 D 3 = 0.80 N 2 = 1.80518 ν 2 = 25.4 R 4 = 4.52 D 4 = 2.21 R 5 = 849.84 D 5 = 2.00 N 3 = 1.60342 ν 3 = 38.0 R 6 = -8.89 D 6 = 0.26 R 7 = -6.42 D 7 = 0.80 N 4 = 1.77250 ν 4 = 49.6 R 8 = 7.43 D 8 = 0.92 R 9 = 15.81 D 9 = 6.40 N 5 = 1.69895 ν 5 = 30.1 R10 = -8.19 D10 = 1.50 R11 = (Aperture) D11 = 1.50 R12 = 55.46 D12 = 0.80 N 6 = 1.72000 ν 6 = 50.3 R13 = 9.66 D13 = 3.80 N 7 = 1.60311 ν 7 = 60.7 R14 = -12.47 D14 = 0.88 R15 = -15.98 D15 = 0.80 N 8 = 1.84666 ν 8 = 23.8 R16 = 12.36 D16 = 0.15 R17 = 13.86 D17 = 3.80 N 9 = 1.58313 ν 9 = 59.4 R18 = -11.75 D18 = 0.15 R19 = 14.36 D19 = 3.10 N10 = 1.51742 ν10 = 52.4 R20 = -29.30 D20 = 5.00 R21 = ∞ D21 = 6.00 N11 = 1.51633 ν11 = 64.2 R22 = ∞ Distance between R20 surface and image plane: 12.0 mm in Air Exit pupil position (from image plane): -45.3 mm <Numerical example 2 〉 F = 6.20 fno = 1: 1.65 2 ω = 68.2 ° R 1 = 15.53 D 1 = 3.10 N 1 = 1.60342 ν 1 = 38.0 R 2 = 611.16 D 2 = 0.15 R 3 = 12.15 D 3 = 0.80 N 2 = 1.80518 ν 2 = 25.4 R 4 = 4.53 D 4 = 2.16 R 5 = 122.10 D 5 = 1.90 N 3 = 1.60342 ν 3 = 38.0 R 6 = -11.24 D 6 = 0.34 R 7 = -6.79 D 7 = 0.80 N 4 = 1.77250 ν 4 = 49.6 R 8 = 6.59 D 8 = 1.21 R 9 = 17.24 D 9 = 4.23 N 5 = 1.69895 ν 5 = 30.1 R10 = -7.55 D10 = 1.50 R11 = (aperture) D11 = 1.50 R12 = 103.86 D12 = 0.80 N 6 = 1.72000 ν 6 = 50.3 R13 = 9.65 D13 = 3.80 N 7 = 1.60311 ν 7 = 60.7 R14 = -10.64 D14 = 0.10 R15 = -20.14 D15 = 0.80 N 8 = 1.84666 ν 8 = 23.8 R16 = 10.95 D16 = 0.22 R17 = 12.84 D17 = 3.80 N 9 = 1.58313 ν 9 = 59.4 R18 = -12.01 D18 = 0.15 R19 = 15.66 D19 = 3.10 N10 = 1.51742 ν10 = 52.4 R20 = -22.13 D20 = 5.00 R21 = ∞ D21 = 6.00 N11 = 1.51633 ν11 = 64.2 R22 = ∞ Distance from R20 plane to image plane: 11.7 mm in Air Exit pupil position (from image plane): -46.8 mm

[0032]

[Table 1]

[0033]

According to the present invention, by properly setting the lens configuration as described above, the back focus is long enough to allow various optical members such as filters to be arranged between the taking lens and the image pickup surface. In addition, a wide angle of view with a shooting angle of view of about 70 degrees and an F number of about 1.6, which is designed to reduce the diameter of the front lens and to reduce the size of the entire lens system, is excellent in correcting various aberrations of the entire screen. It is possible to achieve a retrofocus wide-angle lens having optical performance.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is an aberration diagram of the numerical example 1 at infinite object distance.

FIG. 3 is an aberration diagram when the object distance in Numerical Example 1 is 20 mm from the object distance when it is entirely extended.

FIG. 4 is an aberration diagram at the time of rear focus of 20 mm from the object distance in Numerical Example 1.

FIG. 5 is an aberration diagram of the numerical value example 1 when floating 20 mm from the object distance.

FIG. 6 is an aberration diagram for an object distance of infinity according to Numerical Example 2 of the present invention.

FIG. 7 is an aberration diagram of Numerical example 2 when the entire object distance is 20 mm.

FIG. 8 is an aberration diagram of Numerical example 2 when rear focusing with an object distance of 20 mm.

FIG. 9 is an aberration diagram of Numerical example 2 when an object distance is 20 mm in a floating state.

[Explanation of symbols]

 L1 First group L2 Second group SP Aperture IP Image plane d d line g g line ΔM Meridional image plane ΔS Sagittal image plane

Claims (3)

[Claims] 1. A positive first lens having a convex surface having a strong refractive power directed to the object side, a meniscus negative second lens having a convex surface directed to the object side, and a strong refractive power facing the image surface side in order from the object side. , The third lens with the convex surface facing toward it, the negative fourth lens with both surfaces facing toward the concave surface, the fifth lens with both surfaces facing toward the positive surface, the diaphragm, and the meniscus negative lens with the convex surface facing the object side. A cemented lens in which a sixth lens and a positive seventh lens whose both lens surfaces are convex surfaces are cemented, a negative eighth lens whose both lens surfaces are concave surfaces,
Retrofocus, characterized in that it is composed of 9 groups of 9 lenses, that is, a positive 9th lens with both convex lens surfaces, and a positive 10th lens with both convex lens surfaces facing the object side and having a strong refractive power. Type wide-angle lens. 2. A condition of 0.7 <| R ₄₁ / R ₄₂ | <1.2, where R ₄₁ and R ₄₂ are curvature radii of the object-side and image-side lens surfaces of the fourth lens, respectively. The retrofocus wide-angle lens according to claim 1, which is satisfied. 3. A condition of 0.9 <| R ₉₁ / R ₉₂ | <1.4, where R ₉₁ and R ₉₂ are the radii of curvature of the object-side and image-side lens surfaces of the ninth lens, respectively. The retrofocus wide-angle lens according to claim 1, which is satisfied.