JP3082997B2 - Wide-angle 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 wide-angle lens suitable for a photographic camera or the like, and more particularly, to an F-number of more than 100.
The present invention relates to a compact wide-angle lens having a good optical performance of about 6 and a small number of components such as about 4 lenses.

[0002]

2. Description of the Related Art In recent years, compact cameras equipped with a panorama mechanism or cameras dedicated to panorama have been spotlighted. In order to sufficiently exhibit the effect in panoramic photography, it is desirable that the photographing lens has a sufficiently wide angle of view.

[0003] As a wide-angle lens having an angle of view of 90 ° or more for a single-lens reflex camera, a so-called retro-focus type is commercialized. Because of the large number of components, it is not very suitable for use in compact cameras that do not require a particularly long back focus.

On the other hand, a symmetrical lens is widely known as another single lens having a wide angle of view, particularly as a lens having a simple configuration with a small number of lenses.

For example, US Pat. No. 2,031,792 discloses a wide-angle lens composed of four meniscus lenses of two front groups, positive and negative, and two rear groups, negative and positive.
Japanese Patent No. 16264 discloses a lens composed of a total of five lenses including three lenses in the rear group. Further USP3
No. 661447 discloses a three-element construction including a negative meniscus lens, a positive lens, and a negative meniscus lens.
A wide-angle lens with a simple configuration is proposed.

In Japanese Patent Application Laid-Open No. 2-230208, an angle of view of 60 ° F / 4.5 composed of four negative meniscus lenses, a positive lens, a positive lens, and a negative meniscus lens is disclosed.
A wide-angle lens is proposed.

[0007]

SUMMARY OF THE INVENTION However, US
The wide-angle lenses disclosed in P2031792, US Pat. No. 2,216,264, and the like are composed of a meniscus lens having a very large curvature, so it is difficult to process the lens, which increases the cost, and it is difficult to hold the lens with high accuracy. There was a problem.

Although the three-lens lens proposed in US Pat. No. 3,661,497 is certainly simple in construction, it does not allow a diaphragm for mechanically changing the aperture.

On the other hand, a four-element lens disclosed in Japanese Patent Application Laid-Open No. 230230/1990 has a small number of elements and a relatively small curvature, but has an angle of view of only about 60 °, and a plurality of lenses. Requires a spherical surface.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a wide-angle lens having a simple structure.
As described above, the present invention relates to a wide-angle lens having a sufficient optical performance up to the periphery even with an F number of about 5.6.

[0011]

A wide-angle lens according to the present invention comprises a negative meniscus first lens having a convex surface facing the object side in order from the object side, a second lens having a positive refractive power, and a positive refractive power. A third lens having a negative meniscus fourth lens having a convex surface facing the image side, an aperture stop disposed between the second lens and the third lens, a focal length of the entire system being f, and a first lens being 0.61 <| f ₁ / f | <1 (1) 0.09 <| d / f | <0 where f _{1 is} the focal length of the lens and d is the air gap between the second lens and the third lens. ... (2) is to satisfy the following condition.

[0012]

FIG. 1 is a sectional view of a first numerical embodiment according to the present invention. In this embodiment, a negative meniscus first lens having a negative refractive power and a convex surface facing the object side in order from the object side, a second lens having a positive refractive power and an aspheric object side surface, an aperture stop, and a positive lens And a fourth lens having a negative refractive power and a convex surface facing the image side.

According to the present invention, by disposing such a substantially symmetrical lens arrangement, distortion and the like accompanying widening of the angle can be satisfactorily corrected. The lens diameter is made to be more advantageous than the reverse case of the combination.

By introducing an aspherical surface on the object side surface of the second lens, it is possible to satisfactorily correct spherical aberration and coma.

Further, in order to obtain good optical performance while widening the angle and miniaturizing the lens system, the conditional expression (1) described above is required.
(2) is satisfied.

If the refracting power of the first lens becomes too weak beyond the upper limit of the conditional expression (1), it becomes difficult to correct the Petzval sum and the outer diameter of the first lens becomes large. Conversely, if the refractive power of the first lens exceeds the lower limit and becomes too strong, it becomes difficult to correct spherical aberration, coma, astigmatism, and surface curvature in a well-balanced manner. If the upper limit of conditional expression (2) is exceeded, it will be difficult to correct the coma and astigmatism in a well-balanced manner. Conversely, if the lower limit of conditional expression (2) is exceeded, a sufficient space for disposing the aperture stop will not be obtained.

The wide-angle lens according to the present invention is achieved by satisfying the above-mentioned conditions, but in order to further correct various aberrations in a well-balanced manner, the aspherical surface on the object side surface of the second lens should be within a range of 80% or less of the effective diameter. In order to correct spherical aberration and coma aberration, it is desirable to make the shape such that the positive refractive power becomes weaker toward the periphery.

The second lens and the first lens may be plastic molded lenses. At this time, it is more advantageous to make both of them plastic than to make only one of them plastic lenses, considering the effects of temperature and humidity.

Next, numerical examples of the present invention will be described. 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 spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass.

The aspherical surface has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, and R as a paraxial radius of curvature.
When A, B, C, D, and E are each aspheric coefficients

[0021]

[Outside 1] It is represented by the following expression.

Table I shows numerical examples and conditional expression (1).
The relationship with (2) is shown.

[0023]

[Outside 2]

[0024]

[Outside 3]

[0025]

[Outside 4]

[0026]

[Table 1]

[0027]

According to the present invention, by forming the four lenses and the aperture stop in the shape and arrangement as described above, a compact wide-angle lens having good optical performance with an angle of view of 100 ° or more and F5.6 or more. A lens can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a wide-angle lens according to the present invention.

FIG. 2 is a diagram showing various aberrations of Numerical Example 1 according to the present invention;

FIG. 3 is a diagram illustrating various aberrations of Numerical Example 2 according to the present invention.

FIG. 4 is a diagram showing various aberrations of Numerical Example 3 relating to the present invention.

[Explanation of symbols]

 d d-line g g-line ΔM meridional image plane ΔS sagittal image plane

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (4)

(57) [Claims] 1. A negative meniscus first lens having a convex surface facing the object side, a second lens having a positive refractive power, a third lens having a positive refractive power, and a convex surface facing the image side, in order from the object side. It is composed of the fourth lens of a negative meniscus, and the aperture stop as well as arranged between the second lens and the third lens, the focal length of the entire system f, a focal length of the first lens
The f _1, when the air gap of the second lens and the third lens set to _{d, 0.63 <| f 1 /} f | <1 0.09 <| d / f | < satisfies 0.2 condition: A wide-angle lens. 2. The wide-angle lens according to claim 1, wherein an aspheric surface is provided on an object-side surface of said second lens. 3. The wide-angle lens according to claim 2, wherein the aspherical surface of the second lens has a shape such that the positive refractive power becomes weaker toward the periphery within a range of 80% of the effective diameter. 4. A camera comprising the wide-angle lens according to claim 1.