JPS6239366Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a large-diameter lens for close-up photography used in facsimile input devices and the like. Conventionally, facsimile devices were generally installed in the same location as telephones, and the devices themselves were large, so when using them, the originals had to be carried to the location where the devices were installed, and the facsimile devices had to be carried to the location where the documents were located. This usage is not normally used. Furthermore, it is impossible to transfer the image information of the three-dimensional object itself, which cannot take the form described on paper. Therefore, it was sufficient for the lens system employed in the optical system of a facsimile machine to focus only on resolving power and cost. On the other hand, if the facsimile input device could be miniaturized and used as a portable device in the same way as a copy camera, it would be possible to
It is now possible to convert a three-dimensional object into two-dimensional image information, and it can also be carried freely. In order to achieve such miniaturization, it is conceivable to adopt a mechanism similar to that of well-known single-lens reflex cameras. The lens system that should be compatible with this system must have a back focus long enough to ensure mirror movement space, a large aperture that can be exposed even under natural light, a high peripheral illuminance ratio, and high resolution. It needs to be lightweight and compact. However, conventional facsimile lenses cannot be used in the above optical system because of their short back focus and small aperture. The purpose of this invention is to overcome the above-mentioned drawbacks and to create a compact portable facsimile input device in the form of a single-lens reflex camera. It is an object of the present invention to propose a compact large-diameter lens for close-up photography that has both the peripheral illumination ratio, the long back focus and large aperture that single-lens reflex camera lenses have as their characteristics, and is compact. The feature of the present invention is that the lens system includes, in order from the object side, a first lens group having a negative focal length, a second lens group having a positive focal length, and a third lens group having a positive focal length. The first lens group includes, in order from the object side, a first lens and a second lens of two concave meniscus lenses with a convex surface facing the object side, and a third lens of a biconvex lens, or a third lens with a convex surface facing the object side. The second lens group is a large aperture lens consisting of a fourth lens, which is a biconvex lens, and a fifth lens, which is a biconcave lens, in order from the object side, and has a long back focus and working distance. be. The present invention will be explained below with reference to illustrated embodiments. As for the large-diameter lens for close-up photography, Fig. 1 shows the first embodiment, and Fig. 4 shows the fourth embodiment.
The figure shows the second embodiment, and in both embodiments, the lens configuration includes, in order from the object A side, a first lens group having a negative focal length, a second lens group having a positive focal length, and a positive focal length. A lens system including a third lens group, wherein the first lens group includes two concave meniscus lenses having a convex surface facing the object side in order from the object A side, a first lens 1 and a second lens 2, and a biconvex lens. or a third lens of a convex mechanical lens with a convex surface facing the object side. The second lens group is composed of, in order from the object A side, a fourth lens 4 which is a biconvex lens, and a fifth lens 5 which is a biconcave lens. In the first embodiment, the third lens group includes a convex meniscus lens 6 with a concave surface facing the object A side, a biconcave lens 7, and a biconvex lens 8.
In the second embodiment, a convex meniscus lens 6 with a concave surface facing the object A side, a double concave lens 7 and a double convex lens 8 are cemented together, and a double convex lens or object A. It is composed of three lenses including one convex meniscus lens 9 with a concave surface facing toward the side. The symbols attached to the lenses in FIGS. 1 and 4 above are as follows. r: radius of curvature of each single lens, r ₇ ; radius of curvature on the object side of the fourth lens, r ₈ ; radius of curvature on the image side of the fourth lens, r ₉ ; radius of curvature on the object side of the fifth lens, d; Distance between each surface, d ₄ ; Distance from the image side surface of the second lens to the object side surface of the third lens. The numerical values of each lens in the first embodiment shown in FIG. 1 above are as follows. However, the sign is: n: refractive index of d-line of each single lens n ₄ ; refractive index of d-line of the fourth lens, ν: Atsube number of d-line of each single lens

[Table] Combined focal length of all lens systems f = 1.0, F number - F _NO = 1.87, optimum magnification = -0.0807, aperture is 9th
The front of the plane is 0.0477, the back focus f _B = 1.0694 when the optimum magnification is satisfied, and the numerical values of each lens in the second embodiment shown in Fig. 4 are as follows:

[Table] Combined focal length of all lens systems f = 1.0, F number F _NO = 1.87, back focus f _B = 1.0732,
Optimal magnification = -0.0807, aperture is in front of the 9th surface
0.0656, The conditions for a large aperture lens for close-up photography that satisfies the first and second embodiments are as follows. (1) 0.6f＜r ₇ ＜0.9f (2) 0.9＜r ₈ /r ₉ ＜1.4 (3) n ₄ ＞1.7 (4) d ₄ ＞0.18f To explain the above conditional expression, (1) 0.6f The conditions <r ₇ <0.9f are: 1. Mainly related to spherical aberration and coma aberration. That is, when the lower limit is exceeded, spherical aberration and comatic aberration become significantly undervalued. In order to correct this, the first or second concave meniscus lens must be made stronger. As a result, the spherical aberration and the coma aberration on the upper line side can be corrected, but the coma aberration on the underline side becomes increasingly under-corrected, making it difficult to correct. If the upper limit is exceeded, not only will spherical aberration and comatic aberration become significantly excessive, but also negative distortion will become stronger, and if the convex meniscus lens of the third group is bent to correct this distortion, the Petzval sum will increase. However, the image plane becomes significantly under-imaged. 2. In order to obtain a large peripheral illumination ratio and high resolution at the periphery, the curvature of field must be sufficiently corrected, and the coma aberration on the upper and lower line sides must be appropriately balanced. (2) The condition 0.9<r ₈ /r ₉ <1.4 mainly concerns astigmatism and coma. _R8 and _R9 face each other with approximately the same radius of curvature across the diaphragm, and the refractive index of the lens medium is approximately the same, so by applying bending, astigmatism can be reduced by the effects of higher-order aberrations. It shows little fluctuation, and the fluctuation of coma aberration shows symmetry between the upper line side and the under line side. Therefore, by appropriately providing r ₈ and r ₉ , a large contribution is made to the balance of off-axis aberrations. That is, when the lower limit is exceeded, both astigmatism and coma aberration become over, and when the upper limit is exceeded, they become under. (3) n ₄ >1.7 (4) d ₄ >0.18f The condition mainly concerns spherical aberration and back focus. It is a well-known fact that in order to increase the aperture of a lens system, the refractive index of the medium of each component lens should be increased, but this was set as a condition for the refractive index of the fourth lens, which has a particularly strong power ( 3). In addition, _d4 not only makes a large contribution to spherical aberration, but also makes a large contribution to back focus, so when the back focus is required to be approximately equal to the focal length, as in this lens system, it is important to consider the balance with spherical aberration. An appropriate value must be selected while taking this into account, and condition (4) expresses this. That is, in condition (3), if the lower limit is exceeded,
This results in the occurrence of annular spherical aberration, an increase in the flare component of comatic aberration, and an increase in the Petzval sum.If the lower limit of condition (4) is exceeded, the back focus becomes insufficient and the spherical aberration becomes excessive. Since the present invention is configured as described above, the peripheral light amount ratio is large, so that a sufficient amount of light enters the periphery of the image receiving element. Furthermore, since the back focus is long, space for the mirror movable part can be easily secured. Also, since it has a large aperture, there is no need to strongly illuminate the subject. Furthermore, since the lens has high resolution, it is possible to provide a large-diameter lens for close-up photography that has excellent practical effects, such as being compatible with high-performance image receiving elements.

[Brief explanation of drawings]

Fig. 1 is a lens configuration diagram of the first embodiment of a large-diameter lens for close-up photography, Fig. 2 is an aberration diagram of the first embodiment, and Fig. 3 is a spatial transfer function (MTF) when normalized to an image height of 10.7 mm. ) curve diagram, FIG. 4 is a lens configuration diagram of the second embodiment, FIG. 5 is an aberration diagram in the second embodiment, and FIG. 6 is a spatial transfer function curve diagram in the second embodiment. 1, 2...Concave meniscus lens, 3...Biconvex lens or convex meniscus lens, 4...Biconvex lens, 5...Biconcave lens,...First lens group,
...Second lens group, ...Third lens group, r...
Radius of curvature, n...Refractive index, ν...Atsube number.

Claims (1)

[Claims for Utility Model Registration] A lens system that includes, in order from the object side, a first lens group with a negative focal length, a second lens group with a positive focal length, and a third lens group with a positive focal length. The first lens group includes, in order from the object side, a first lens and a second lens of two concave meniscus lenses with a convex surface facing the object side, and a third lens of a biconvex lens or a convex lens with a convex surface facing the object side. The second lens group is composed of a first lens that is a biconvex lens and a fifth lens that is a biconcave lens in order from the object side, so that the composite focal length of the entire lens system is f, The radius of curvature on the object side of the fourth lens is r ₇ , the radius of curvature on the image side of the fourth lens is r ₈ , the radius of curvature on the object side of the fifth lens is r ₉ ,
When the d-line refractive index of the fourth lens is n ₄ and the distance from the image side surface of the second lens to the object side surface of the third lens is d ₄ , (1) 0.6f<r ₇ <0.9f (2) 0.9 A large aperture lens for close-up photography that satisfies the following conditions: ＜r ₈ / r ₉ ＜1.4 (3) n ₄ ＞1.7 (4) d ₄ ＞0.18f.