JP2790453B2 - Super wide angle lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-wide-angle lens used for monitoring and the like. 2. Description of the Related Art In recent years, lightweight and compact lenses have been desired for camera lenses for surveillance and vehicles. Conventionally, as a lens used for surveillance and on-vehicle use, an ordinary video camera lens or the like has been substituted, or a lens having a long focal length, that is, a small angle of view has been adopted. Problems to be Solved by the Invention However, the above-mentioned lenses are required to have an ultra-wide angle, and this kind of lens is required to have a longer back focus compared to the focal length, and the conventional wide-angle lens With an angle of view of over 120 °, there was no lens with an F / 1.4 brightness. In order to obtain such a lens, there is a problem that the number of lenses increases, and the lens must be dark. Further, there is a problem that the lens becomes large because the entire length of the lens is long and the lens diameter is large. In view of the above problems, the present invention reduces the number of lenses, reduces the overall length of the lens even though the back focus is three times as long as the focal length, and furthermore, suppresses distortion to a very wide angle. A lens is provided. Means for Solving the Problems The present invention is divided into a front group having a negative refractive power and a rear group having a positive refractive power in order from the object side, wherein the front group is an aspherical negative meniscus lens, , A cemented lens of a positive lens and a negative lens, and a cemented lens of a negative meniscus lens and a positive lens, and the rear group was provided with five lenses including two sets of the cemented lenses. It is characterized by the following. The present invention provides an aspherical surface on the first surface of the front lens group according to the above-described configuration, whereby the number of lenses can be reduced, sufficient brightness can be obtained, and the overall length of the lens can be shortened. This makes it possible to realize an ultra-wide-angle lens that is small and lightweight and very compact. In addition, the present invention introduces an aspheric surface in order to suppress the deterioration of various aberrations due to the reduction in the number of lenses, and enhances the degree of freedom in design, thereby favorably correcting distortion and coma at an ultra-wide angle, particularly distortion. Can be satisfactorily corrected to about 1/3 of the conventional lens system. Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to FIG. 1 and FIG. FIG. 1 shows a cross section of a lens of this embodiment, and FIGS. 2 (a), (b) and (c) show various aberrations of the lens. In FIG. 1, A is a front group having a negative refractive power as a whole, B is a rear group having a positive refractive power as a whole,
The front unit A includes a negative meniscus lens A having an aspheric surface R1 on the object side.
1. Consisting of a negative meniscus lens A2, a bonded lens A3 of a positive lens and a negative lens, and a bonded lens A of a negative meniscus lens and a positive lens, and the rear group B includes a negative meniscus lens and a positive lens It comprises a cemented lens B1, a cemented lens B2 of a negative meniscus lens and a positive lens, and a positive lens B3. Since this embodiment is intended for a video camera, a parallel plane lens C is disposed behind the final lens. In FIG. 2, ΔS denotes a sagittal image plane, and ΔM denotes a meridional image plane. The shape of the aspheric surface is such that the optical axis direction is the X axis, the direction perpendicular thereto is the Y axis, the paraxial radius of curvature is R, the height from the optical axis is H,
When the amount of displacement of the optical axis from the lens surface vertex reference O and X _O, Is represented by Here, K is a conical constant, and A, B, C, and D are aspheric coefficients. Table 1 shows specific numerical values of this embodiment. In Table 1, Ri is the radius of curvature of the ith lens surface from the object side (m
m) and Di are the i-th lens thickness and air gap (mm) in order from the object side, and ni and νi are the refractive index and Abbe number of the glass of the i-th lens in order from the object side. Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 shows a lens section, and FIGS. 4 (a), (b),
(C) shows various lens aberrations. This embodiment is basically the same as the first embodiment, except that the rear unit B includes a cemented lens B4 of a negative lens and a positive lens, a cemented lens B2 of a negative meniscus lens and a positive lens, and a positive lens B3. And the only difference is the laminated lens B4. Table 2 shows specific numerical values of this embodiment. As described above, according to the above embodiment, the front group is divided into a front group having a negative refractive power and a rear group having a positive refractive power. The front unit has an aspherical surface on the first surface, which realizes a high-performance ultra-wide-angle lens with a long back focus, a short overall lens length, and low distortion. it can. Effect of the Invention As described above, the present invention is divided into a front group having a negative refractive power and a rear group having a positive refractive power, and the front group is sequentially an aspheric negative meniscus lens, a negative meniscus lens, A lens in which a cemented lens of a positive lens and a negative lens, a cemented lens of a negative meniscus lens and a positive lens are arranged, and the rear group includes five lenses including two sets of cemented lenses. To provide an ultra-wide-angle lens that can reduce the number of lenses and has a short overall lens length despite a long back focus, is very compact, and is bright, has a large aperture and good aberration performance. The practical effect is great.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a lens according to a first embodiment of the present invention, FIG. 2 is a diagram showing various aberrations, FIG. 3 is a sectional view of a lens according to a second embodiment of the present invention, FIG. The figure shows the various aberration diagrams. A: front group, B: rear group, A1, A2: negative meniscus lens, A3: laminated lens of positive lens and negative lens,
A4: Negative meniscus lens and positive lens bonded lens, B1, B2, B4: bonded lens, B3 ... positive lens.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Saburo Kinoshita               3-8-8 Ninomiya Higashi, Akigawa-shi, Tokyo Yes               Limited company Kinoshita Optical Laboratory                (56) References JP-A-57-197508 (JP, A)                 Tokiko Sho 41-3827 (JP, B1)

Claims (1)

(57) [Claims] The front group is divided into a front group having a negative refractive power and a rear group having a positive refractive power in order from the object side, and the front group includes an aspherical negative meniscus lens, a negative meniscus lens, a positive lens and a negative lens in order. An ultra-wide-angle lens comprising a cemented lens, a cemented lens of a negative meniscus lens and a positive lens, and the rear group includes five lenses including two sets of cemented lenses.