JPH11326756A - Wide-angle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-angle lens whose angle of view exceeds 100 deg. without making it larger by satisfying a specified condition concerning the focal distance of an entire lens system, the synthetic focal distance and the radii of curvature of respective lenses. SOLUTION: This lens is composed of 1st to 3rd lenses 11 to 13, a 1st composite lens 21 constituted by bonding 4th and 5th lenses 14 and 15, a 2nd composite lens 22 constituted by bonding 6th and 7th lenses 16 and 17, and a 8th lens 18. It satisfies respective conditional expressions; fB/f>0.8, 0.5>|f12 |/f<1.2, 0.7<R2 /R4 <1.2, ν6 -ν7 >12, N4>1.7 and N6>1.7. In the expressions, f0 means the focal distance of the entire lens system, fB means the back focus thereof, f12 means the synthetic focal distance of the 1st and the 2nd lenses 11 and 12, R2 and R4 mean the radii of curvature of the image-side surfaces of the 1st and the 2nd lenses 11 and 12, ν6 and ν7 mean the Abbe numbers of the 6th and 7th lenses 16 and 17, and N4 and N6 mean the refractive indexes of the 4th and the 6th lenses 14 and 16 to a d-line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-angle lens suitable for a camera.

[0002]

2. Description of the Related Art As a wide-angle lens mounted on a camera,
JP-A-5-134175 and JP-A-8-2861
A wide-angle lens described in Japanese Patent Publication No. 05-2005 is exemplified. These wide-angle lenses are composed of about 7 to 8 small lenses, and are configured so that the angle of view is about 80 °. Recently, a wide-angle lens having a wider angle of view has been desired.

[0003]

However, generally, 10
In a wide-angle lens having an angle of view exceeding 0 °, the diameter of the rear lens and the diameter of the front lens become large, so that the whole becomes large, which is not preferable for a camera. In addition, since the back focus is shortened, for example, when used in a camera that extracts light reflected from the film surface or a part of a photographing light beam and performs photometry.
It becomes impossible to secure a space for disposing a photometric element on the image side of the lens system.

The present invention has been made in view of the above circumstances, and has as its object to provide a wide-angle lens having an angle of view exceeding 100 ° without increasing the size.

[0005]

In order to achieve the above object, a wide-angle lens according to the present invention comprises, in order from an object side, a convex surface facing the object side, a first meniscus lens having a negative refractive power, and a second lens. Two lenses, a third lens having a positive refractive power with a convex surface facing the object side, a fourth lens having a positive refractive power with a convex surface facing the object side, and a fifth lens having a negative refractive power are joined. A first compound lens, a second compound lens obtained by joining a sixth lens having a positive refractive power with a convex surface facing the object side and a seventh lens having a negative refractive power, and a concave surface facing the object side. An eighth lens having at least one surface formed in an aspherical shape and having a negative refractive power has a focal length of the entire lens system of f, a back focus of f _B , and a first lens and a second lens. Is the combined focal length of f ₁₂ , the radius of curvature of the image-side surface of the first lens is R ₂ , The radius of curvature of the image-side surface of the two lenses is R ₄ , the Abbe number of the sixth lens is ν ₆ , the Abbe number of the seventh lens is ν ₇ , the refractive index of the fourth lens with respect to the d-line is N ₄ ,
The refractive index at the d-line of the sixth lens is taken as _{N 6, f B / f>} 0.8 0.5 <| f 12 | / f <1.2 0.7 <R 2 / R 4 <1 0.2 ν ₆ −ν ₇ > 12 N ₄ > 1.7 N ₆ > 1.7

[0006]

In the present invention, the meniscus first lens and the second lens having a negative refractive power are arrayed from the object side of the lens system, and the negative refractive power is concentrated on the object side, so that the entire lens system is formed. A wide angle of view exceeding 100 ° can be obtained without increasing the diameter. Further, by configuring a lens system in which a lens having an aspherical surface on the image side is arranged, each aberration is satisfactorily corrected, and a high-performance lens is obtained. Condition 0.5 <| f ₁₂ | when / f <exceeds the lower limit of 1.2, have too strong negative refractive power of the first lens and the second lens, difficult to correct aberrations of the entire lens system Become. Further, since the curvature of the image-side surfaces of the first lens and the second lens becomes strong, it becomes difficult to polish the lens surfaces, and it becomes impossible to maintain a high surface accuracy. On the other hand, when the value exceeds the upper limit of the conditional expression, the aberration correction becomes easy, but the diameter of the first lens, the second lens, and the third lens increases, and the entire lens system increases in size.

If the lower limit of conditional expression 0.7 <R ₂ / R ₄ <1.2 is exceeded, the curvature of the image-side surface of the first lens becomes too strong, and polishing of the lens surface becomes difficult. , The surface accuracy cannot be maintained at a high level. On the other hand, when the value exceeds the upper limit of the conditional expression, distortion increases, and it cannot be suppressed.

When the conditional expression ν ₆ −ν ₇ > 12 is not satisfied, the chromatic aberration of off-axis magnification increases and cannot be corrected.

If any one of the conditional expressions N ₄ > 1.7 N ₆ > 1.7 is not satisfied, the Petzval sum becomes large, and astigmatism and field curvature deteriorate. Correction becomes difficult.

If the conditional expression f _B /f>0.8 is not satisfied, the diameter of the rear lens becomes large and the whole lens system becomes large. In addition, it becomes impossible to secure a space for disposing a photometric element on the image side of the eighth lens.

[0011]

FIG. 1 shows the configuration of a wide-angle lens according to the present invention. The wide-angle lens 10 is configured by arranging eight lenses from a first lens 11 to an eighth lens 18 in order from the object side. First lens 11 and second lens 12
Are each composed of a meniscus negative lens having a convex surface facing the object side, and the third lens 13 is composed of a positive lens having a convex surface facing the object side. The fourth lens 14 is a positive lens having a convex surface facing the object side, and the fifth lens 15 is a negative lens. The sixth lens 16 is a positive lens having a convex surface facing the object side, and the seventh lens 17 is a negative lens. The eighth lens 18 is a negative lens having a concave surface facing the object side, and at least one surface is formed in an aspherical shape.

The fourth lens 14 and the fifth lens 15 are joined to form a first compound lens 21. The sixth lens 16 and the seventh lens 17 are joined to form a second compound lens 22. An aperture 25 is arranged between the first compound lens 21 and the second compound lens 22.

The wide-angle lens 10 has a focal length f of the entire lens system, a back focus f _B , a combined focal length of the first lens 11 and the second lens 12 f ₁₂ , and a first lens 1
The curvature radius of the image-side surface of the first lens 12 is R ₂ , the curvature radius of the image-side surface of the second lens 12 is R ₄ , and the Abbe number of the sixth lens 16 is ν.
₆ , the Abbe number of the seventh lens 17 is ν ₇ , and the fourth lens 14 is
When the refractive index of the sixth lens 16 for the d-line is N ₄ and the refractive index of the sixth lens 16 for the d-line is N ₆ , f _B /f>0.8 0.5 <| f ₁₂ | / f <1.2 0.7 is configured _{<R 2 / R 4 <1.2} ν 6 -ν 7> 12 N 4> 1.7 N 6> 1.7 becomes the condition is satisfied.

"First Embodiment" The specifications of the wide-angle lens of the first embodiment are as follows. _{f = 15.27 f B = 13.58 f} 12 = -10.00 R 2 = 10.243 R 4 = 12.219 ν 6 = 46.50 ν 7 = 27.53 N 4 = 1.80420 N 6 _{= 1.80420 F NO = 4.10 2ω =} 110.2 °

In the above data, F _NO is the F number,
2ω indicates the angle of view.

The wide-angle lens according to the first embodiment has the characteristic values "f _B / f", "| f ₁₂ | / f" and "R ₂ / R" of the present invention.
₄ ", the value of" [nu ₆ -v ₇ "is, f _B / f ≒ 0.89 | a _{/ f ≒ 0.65 R 2 / R} 4 ≒ 0.84 ν 6 -ν 7 ≒ 19 | f 12 It is configured to be.

Further, the respective values of N ₄ and N ₆ are configured such that N ₄ ≒ 1.80 N ₆ ≒ 1.80.

Table 1 below shows the lens data of the wide-angle lens according to the first embodiment. The surface number i is a number assigned to each lens surface in order from the object side, and the surface distance D represents the lens thickness or air space between the next surface (unit is m).
m).

[0019]

[Table 1]

For the aspherical surface, the conditional expression Z = ch ² / [1+ ｛1- (1 + K) c ² h ² ｝ ^1/2 ]
+ Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰ . In the equation, c represents the reciprocal of the radius of curvature (= 1 / R), and h represents the height of the light beam from the optical axis. Table 2 shows the aspheric coefficient.

[0021]

[Table 2]

FIG. 2 shows aberration diagrams of the wide-angle lens according to the first embodiment. In FIG. 2, (A) shows the spherical aberration,
(B) represents astigmatism, and (C) represents distortion. Further, in the spherical aberration diagram of (A) in the figure, symbols d and g are d line (587.6 nm) and g line (4
35.8 nm), and S and T in the astigmatism diagram of FIG. 3B represent aberrations with respect to the spherical and meridional image planes, respectively.

[Second Embodiment] FIG. 3 shows a second embodiment of the configuration of the wide-angle lens according to the present invention. The reference numerals in FIG. 3 are used in common with the first embodiment shown in FIG. . The specifications of the wide-angle lens according to the second embodiment are as follows. _{f = 15.30 f B = 13.00 f} 12 = -15.70 R 2 = 10.243 R 4 = 12.218 ν 6 = 46.50 ν 7 = 27.53 N 4 = 1.80420 N 6 = 1.80420 F _NO = 4.55 2ω = 110.1 °

In the wide-angle lens according to the second embodiment, each of the characteristic values is expressed as f _B /f≒0.85|f ₁₂ | /f≒1.03 R ₂ / R ₄ １．０1.05 ν ₆ −ν _The configuration is such that ₇ ≒ 16.4 N ₄ ≒ 1.80 N ₆ ≒ 1.80.

Table 3 shows the lens data of the wide-angle lens of the second embodiment, and Table 4 shows the aspherical coefficient.

[0026]

[Table 3]

[0027]

[Table 4]

FIG. 4 shows aberration diagrams of the wide-angle lens according to the second embodiment.

[Third Embodiment] FIG. 5 shows a third embodiment of the configuration of the wide-angle lens of the present invention. The reference numerals in FIG. 5 are used in common with the first embodiment shown in FIG. .

The specifications of the wide-angle lens according to the third embodiment are as follows. _{f = 15.30 f B = 14.50 f} 12 = -12.75 R 2 = 11.200 R 4 = 10.899 ν 6 = 46.50 ν 7 = 30.05 N 4 = 1.71300 N 6 _{= 1.80420 F NO = 4.57 2ω =} 110.1 °

In the wide-angle lens according to the third embodiment, each of the characteristic values is f _B /f≒0.95|f ₁₂ | /f≒0.83 R ₂ / R ₄ １．０1.03 ν ₆ -ν _The configuration is such that ₇ ≒ 16.4 N ₄ ≒ 1.713 N ₆ ≒ 1.80.

Table 5 shows the lens data of the wide-angle lens of the third embodiment, and Table 6 shows the aspheric coefficient.

[0033]

[Table 5]

[0034]

[Table 6]

FIG. 6 shows aberration diagrams of the wide-angle lens according to the third embodiment.

[0036]

As described above, according to the wide-angle lens of the present invention, a wide angle of view exceeding 100 ° can be obtained with a relatively small number of lenses of eight without increasing the diameter. In addition, it is possible to maintain a good balance of various aberrations. In addition, since a necessary minimum back focus is ensured, a space for disposing a photometric element can be provided on the image side of the eighth lens.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of a first configuration example of a wide-angle lens according to the present invention.

2A and 2B are aberration diagrams of the wide-angle lens of FIG. 1, in which FIG. 2A shows spherical aberration, FIG. 2B shows astigmatism, and FIG. 2C shows distortion.

FIG. 3 is an optical path diagram according to a second configuration example of the wide-angle lens of the present invention.

4A and 4B are aberration diagrams of the wide-angle lens of FIG. 3, in which FIG. 4A shows spherical aberration, FIG. 4B shows astigmatism, and FIG. 4C shows distortion.

FIG. 5 is an optical path diagram according to a third configuration example of the wide-angle lens of the present invention.

6A and 6B are aberration diagrams of the wide-angle lens of FIG. 5, wherein FIG. 6A shows spherical aberration, FIG. 6B shows astigmatism, and FIG. 6C shows distortion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Wide-angle lens 11 1st lens 12 2nd lens 13 3rd lens 14 4th lens 15 5th lens 16 6th lens 17 7th lens 18 8th lens 21 1st cemented lens 22 2nd cemented lens 25 Aperture

Claims (1)

[Claims] 1. A convex surface is directed to the object side in order from the object side,
A first meniscus lens having a negative refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power having a convex surface facing the object side.
A first compound lens formed by joining a lens, a fourth lens having a positive refractive power with a convex surface facing the object side, and a fifth lens having a negative refractive power, and a positive refractive power having a convex surface facing the object side A second compound lens obtained by joining a sixth lens and a seventh lens having a negative refractive power, and a second compound lens having a negative refractive power having a concave surface facing the object side and having at least one surface formed in an aspherical shape. The focal length of the entire lens system is f, the back focus is f _B , and the combined focal length of the first lens and the second lens is f.
₁₂ , the radius of curvature of the image-side surface of the first lens is R ₂ , the radius of curvature of the image-side surface of the second lens is R ₄ , the Abbe number of the sixth lens is ν ₆ , and the Abbe number of the seventh lens is ν ₇ , d of the fourth lens
Assuming that the refractive index for the line is N ₄ and the refractive index for the d-line of the sixth lens is N ₆ , f _B /f>0.8 0.5 <| f ₁₂ | / f <1.2 0.7 _{<R 2 / R 4 <1.2} ν 6 -ν 7> 12 N 4> 1.7 N 6> wide-angle lens, wherein 1.7 becomes possible conditions are satisfied.