JPH0277712A - Superwide-angle photographic lens - Google Patents

Abstract

PURPOSE:To realize a superwide-angle photographic lens at a low-cost by employing two-group, two-element constitution of a concave meniscus lens with negative power as a 1st lens and a biconvex lens with positive power as a 2nd lens and making the lenses meet specific requirements. CONSTITUTION:The lens consists of two elements in two groups, i.e., the 1st concave meniscus lens 20 with the negative power and the 2nd biconvex lens with the positive power in order from the object side to the image side, and >=1 lens surface is made aspherical so as to realize high brightness and a superwide angle. Further, conditional inequalities AB and A hold for the focal length (f) of the whole system, the focal length f2 of the 2nd lens 12, and the surface gap D2 between the image-side lens surface of the 1st lens 10 and the object-side lens surface of the 2nd lens 12. The inequality determines the power distribution and the inequality B prescribed the size of the lens system and the power of each lens.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultra-wide-angle photographic lens. This lens can be used as a lens for door surveillance monitors, a lens for video phone monitors, a visual sensor lens for FA, etc.

[Prior Art] Due to their nature, photographic lenses used for surveillance monitors such as door surveillance monitors, videophone monitors, or FA visual sensors are designed to respond to changes in the usage environment, especially changes in brightness. An extremely bright lens is required. Furthermore, such a lens must have a large photographic range at extremely close distances.

In order to satisfy such requirements, this type of lens has conventionally generally been constructed of three or more lenses.

[Problems to be Solved by the Invention] As described above, the conventional photographing lens of this type has a large number of constituent lenses, which makes it difficult to realize it at low cost.

Furthermore, it is difficult to achieve an extremely short focal length while maintaining optical performance, making it difficult to miniaturize monitors and the like.

The present invention was made in view of the above-mentioned circumstances, and
The objective is to provide a compact ultra-wide-angle photographic lens that can be realized at low cost.

[Means to solve the problem] The present invention will be explained below.

As shown in FIG. 1, the ultra-wide-angle photographing lens of the present invention has a first lens 10 extending from the object side (left side in FIG. 1) toward the image side.
and the second lens 12 are arranged in this order to form a two-group, two-lens configuration.

The first lens 10 is a concave meniscus lens with negative power, and the second lens 12 is a biconvex lens with positive power, and one or more lens surfaces are aspherical.

When the focal length of the entire system is f, the focal length of the second lens is f2, and the distance between the image side lens surface of the first lens and the object side lens surface of the second lens is , then these are (I) 1.0 < f, / f < 2.0 (
II) 'f < 02 < 5f is satisfied.

[Function] The photographic lens is constructed with a small number of lenses (two lenses), and in order to achieve brightness and an ultra-wide angle, one or more lens surfaces are aspheric.

Further, the above condition (I) determines the power distribution, and if the lower limit of this condition (I) is exceeded, the power of the first lens becomes strong, making it difficult to correct various optical aberrations. Furthermore, if the upper limit is exceeded, the optical system becomes larger and the power of the second lens becomes stronger, making it difficult to correct various optical aberrations.

Condition (II) defines the size of the lens system and the power of each lens, and if the lower limit is exceeded, the power of each lens becomes strong, making it difficult to correct various optical aberrations.

Moreover, if the upper limit is exceeded, the entire lens system will become larger.

[Example] Specific examples are given below.

In FIG. 1, reference numeral 20 indicates an aperture, and reference numeral 30 indicates an aperture.
A cover glass of an image sensor such as a CCD is shown.

As shown in Figure 1, the radius of curvature of the first surface from the object side is R3 (i = 1 to 6), and the distance between the surfaces is Di (i = 1 to 5).
, Nj (j=1 to 3) represent the refractive index of the materials of the first and second lenses and the cover glass, respectively. Further, fl represents the focal length of the first lens.

Also, surfaces marked with * represent aspherical surfaces, and each aspherical surface is
It is expressed by the well-known aspherical formula %. X is a coordinate in the optical axis direction with the origin being the intersection of the aspherical surface and the optical axis, and Y is a coordinate in a direction passing through the origin and orthogonal to the optical axis.

C=1/Ri, so each aspherical surface has a radius of curvature Ri near the optical axis, a conic constant, and a higher-order aspherical coefficient E.

Identified by F, G, H.

Example .

i Ri Di j Nj
Material 1 20.0 1.0 1 1.492
Acrylic 2 3.005 8,0 3* 4.909 2.5 2 1.492
Acrylic 4* -4,1555,9 5ooO,8,31,53 Glass 6 ω f=3.3mm, F/No=1.8. f,=-7,
3mm, f2=5.00mmf2/f=1.
515. D2 = '2.424f non-2° on the third surface = -3,14288 E = -8,95738・10-6. F=-7,067
91・1O-8G-1,29,022・10-9. H
= 2.31618・10-9 on the 4th side=-1,58708 E= 2.09416・10-', F= 2.8
2478・1O−6G= 5.39965・10−”
, H=-7,34206・10-"Figures 2 and 3
The figure shows an aberration diagram. As shown in the figure, each aberration is well corrected.

[Effects of the Invention] As described above, according to the present invention, a novel ultra-wide-angle photographing lens can be provided.

Since this lens is composed of two lenses as described above, it can be miniaturized and realized at low cost.

Moreover, by adopting an aspheric surface, it is possible to achieve performance as good as, if not better than, conventional ones.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the lens configuration of the present invention as an example;
FIG. 2 and FIG. 3 are aberration diagrams related to the example.

Claims (1)

[Claims] A first lens and a second lens are arranged in this order from the object side to the image side, the first lens being a concave meniscus lens having negative power, and the second lens being a positive lens. A biconvex lens with a power of , one or more lens surfaces are aspheric, the focal length of the entire system is f, the focal length of the second lens is f_2,
When the distance between the image-side lens surface of the first lens and the object-side lens surface of the second lens is D_2, these are (I) 1.0<f_2/f<2.0 (II) f<D_2 An ultra-wide-angle photographing lens that satisfies the condition <5f.