JPS6088916A - Lens system equipped with auxiliary lens - Google Patents

Abstract

PURPOSE:To correct aberrations excellently and obtain a large conversion ratio of focal length by composing an auxiliary lens to be arranged behind a main lens detachably of a negative, a positive, and a negative lens, and converting the focal length by the auxiliary lens. CONSTITUTION:The auxiliary lens system II consists of the 1st negative lens, the 2nd positive lens, the the 3rd negative lens and aberrations are corrected with good balance. The 1st lens is the negative lens having a concave lens on an image side, the 2nd lens is the biconvex lens, and the 3rd lens is the negative lens having a concave surface on an apeture side. Namely, the air lens between the 1st and the 2nd lenses is formed concentrically about the convergence point of an on-axis light beam, and the air lens between the 2nd and the 3rd lenses is also concentrical about an aperture. The generation of the spherical aberration of the former air lens is less, but the air lens is convex to the aperture, so it is difficult to control the generation of the off-axis aberration. This air lens is arranged at the side of the main lens I , i.e. between the 1st and the 2nd lenses to reduce the off-axis light beam height of this air lens, reducing the generation of the off-axis aberration.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conventional lens system equipped with an auxiliary lens used in a method of converting the focal length by an auxiliary lens that is removably placed behind a main lens. Technology A lens system that is composed of a main lens and an auxiliary lens and whose focal length is changed by inserting and removing the auxiliary lens is disclosed in Japanese Patent Application Laid-open No. 56-94318 and Japanese Patent Application Laid-open No. 56-9.
No. 5210, JP-A-57-. It is known from various publications such as No. 16224.

Among these publications, the lens system described in Japanese Unexamined Patent Publication No. 56-94318 is a lens system having two auxiliary lenses. Since the main lens in such a lens system has its own chromatic aberration corrected, the auxiliary lens also needs to have its own chromatic aberration sufficiently corrected. In this case, it is necessary to correct axial chromatic aberration and lateral chromatic aberration at the same time. For this purpose, both the height of the beam and the slope of the light beam must be adjusted when the beams of different wavelengths exit the auxiliary lens. This requirement is as follows:
A two-sheet disc as in the conventional example cannot fully satisfy the requirements, and therefore cannot satisfactorily correct color ablation. Historically, the correction of the astigmatism difference is insufficient in this conventional method. Also, JP-A-51i No. 95210 and JP-A-57-
The lens system described in Japanese Patent No. 16224 is a lens system that includes three auxiliary lenses. These unique examples are
Auxiliary lens is positive and negative.

Positive lens, 11% composition. The Urasuke lens as a whole has a negative aJl refractive power of .11, so if the negative lens is made of 41" II like these conventional examples, the refractive power of the negative lens will be too large and the Petzval lens (2) becomes smaller, and it is not possible to correct each aberration J in a well-balanced manner.In addition, the curvature of the surface of the shell lens becomes stronger, and the amount of higher-order aberrations increases, making it difficult to correct them, and it is impossible to completely correct residual aberrations. The astigmatism difference is still large in these conventional 1-tari lenses.The main cause of the disadvantage of the astigmatism is that it is a +E, negative + positive lens configuration, but in history there are 14
%-order spherical aberration is likely to occur and off-axis aberration is likely to occur.
ljl An air lens that is easy to L is placed on the main lens side where the 11qlI upper convergence source 1 bracken height is small and the off-axis light height is small, and conversely an air lens that generates small spherical + fi aberrations and 111 + where external aberrations tend to occur is placed on the main lens side. One of the reasons is that the axial ray height is small and the off-axis light beam is large, and the lens is placed at 1 + 1 + aperture (111. .

Purpose The present invention provides an auxiliary lens in which aberrations are well corrected by making the auxiliary lens have a shell, positive, and negative lens configuration, and it is possible to have a large focal length variation ratio. The purpose is to provide lens thread.

General The lens system of the present invention is composed of a main lens 1 and an auxiliary lens (2) as shown in FIG. Among them, the auxiliary lens (2) is composed of a negative lens (first lens), a positive lens (second lens), and a negative lens (third lens) from the main lens 1 side.

By forming the lens with three lenses like this auxiliary lens, chromatic aberration can be sufficiently corrected by the auxiliary lens itself. Also negative the composition of three pieces.

By setting IJE to negative, it is possible to arrange two negative lenses and reduce the individual refractive power of these negative lenses.
It is possible to prevent the Petzval quadrupole from becoming too small and to correct each aberration in a well-balanced manner. Also, residual aberrations can be reduced.

In the lens system of the present invention, among the valley lenses of the auxiliary lenses, as in the embodiment described later, the j-th lens is a concave lens on the image side, the second lens is a biconvex lens, and the third lens is an object nl lens. ! It is more preferable to use a lens with 4 and 2 facing 1 for the following reasons7).

The refractive power of the auxiliary lens composed of these three lenses (〆1, actual '+5, the refractive power of the air lens formed between the first lens and the second lens, and the 1.IX2 lens, This is obtained by the refractive power of the air lens formed between the I!3 lenses.These air lenses tend to cause convergence at =;v.

In order to suppress the occurrence of this secondary convergence red, the valley lens is shaped as described above, and the air lens formed between the first lens and the second lens is placed at the convergence point of the qql upper element H by 7t.
It is desirable to have an L concentric shape, and to make the air lens between the second lens and the 43rd lens concentric with the aperture.

The implementation of the lens system of the present invention described above is based on the lens configuration shown in FIG. 1 and the following data.

(Main lens) f=41.4. /2.85. T Go 1.116 (main lens 10 auxiliary lenses) f2 67.55, /4.66, T = 0.947
Upper M self (D Chi 1-, r1+ r2+ '...,
r14 is the radius of curvature of lens valley 1I11, d + l d
21..., d13 is the flesh of the valley lens) 9 and Kusakima Gō, 12..., l】7 is the valley +1 + 11 +
9 Refractive index of lens, 1. C2. ..., shi7ha valley shi'
7 Snow Sobe, f is the focal length IH, Tld telephoto ratio.

I in the data of this implementation 1y is an example of the main lens (Fig.
ie) In the section, ■ is attached to the auxiliary lens part 〇 This implementation +&! In I, the auxiliary lens thread +1 is used as a negative lens, a positive second lens, and a negative third lens as shown in FIG. 1 to effectively correct aberrations. 4. Turn the lens with the concave surface facing the 1 o side / make it a negative lens, make the 2nd lens a 1i14 convex lens, and C'
It is a shell lens with a concave surface facing the β3 lens. In other words, the air lens between the first lens and the second lens is made to have a shape that is concentric with respect to the convergence point of the axial rays, and the shape of the air lens between the second lens and the third lens is concentric with respect to the air l/lens aperture of M1 of the second lens and the third lens. It is shaped like this. In this example, the air lens shaped like the curved air lens of the; 1 lil monument of the occurrence is difficult. Therefore, in this embodiment, the vital lens having such a shape is placed in one rule of the main lens 1, that is, in the same position as the first lens and the second lens.
By doing so, the height of off-axis rays in this air lens is lowered, thereby reducing the occurrence of off-axis aberrations. In this case, although the axial optical aberration height in this air lens is high, since the occurrence of spherical aberration is small as described above, it can be sufficiently canceled by the air lens between the second lens and the third lens.

Next, the shape of the air lens formed between the 42 lens and the third lens is concentric with respect to the lens. In an air lens having such a shape, the occurrence of aberrations outside of 1HfI is small and can be easily suppressed.

However, since the angle of incidence of the axial optical gland is large, high convergence tends to occur with respect to spherical aberration. Therefore, an air lens having such a shape is arranged at the image +1+1J (between the tb2 lens and the third lens) so that the optical height on the axis here becomes small. In addition, the ray height of the off-axis rays increases, so the amount of off-axis aberrations generated increases, but as mentioned above, the amount of off-axis aberrations generated is not so large, so It is possible to cancel each other out with the off-axis aberration.

As described above, in this embodiment, the air lens, which is disadvantageous to off-axis aberrations, is self-contained on the side closer to the main lens I to reduce the amount of off-axis aberrations generated, and the air lens, which is unfavorable to off-axis aberrations, is hidden on the side closer to the main lens I, thereby reducing the amount of off-axis aberrations generated. The air lens is placed near the 1st corps 4 to suppress the occurrence of forest aberrations, and as a whole, the off-axis aberrations and 9 spherical convergence that occur with the Taniboki lens are reduced to the same extent and cancel each other out. In this way, the residual yield y=k can be reduced to obtain good performance.

Effects of the Invention The lens system of Genmei has 444 auxiliary lenses with a small number of lenses, and is very lance-sized, so it is possible to install it in the camera body together with the main lens, and this auxiliary lens It is possible to easily attach and detach the auxiliary lens between the main lens and the aperture.Also, by making the auxiliary lens negative, stop, and negative, aberrations can be reduced. 1.6 times more than conventional 1u
It is possible to realize a variable magnification ratio larger than ll. Furthermore, as mentioned above, it is compact compared to a normal 2-group zoom lens and has a lens reduction of more than 10%.

[Brief explanation of the drawing]

Figure 1 is a 1t9i diagram of the uninvented lens system, Figure 2 is an aberration curve diagram of an embodiment of the present invention, and Figure 3 is an aberration curve diagram of the main lens used in the above embodiment 1. . Applicant Olympus Kumoto Gaku Kogyo Co., Ltd. Agent Hiroshi Mukai Ni-ball recovery F/2.85 Figure 2, Figure 3, top Astigmatism Distortion 27.6° 27.68

Claims (2)

[Claims] (1) A lens system having a main lens and an auxiliary lens used for converting the focal length by inserting and removing it behind the main lens, in which the auxiliary lens is sequentially arranged from the object +1fl+ to the negative lens Q4 and the positive lens Q4. A lens system characterized by being made up of 3 lenses (2 lenses and a 3rd lens which is a shell lens). (2) The 49t' feature indicates that the first lens is a lens with a concave surface facing the image side, the second lens is a biconvex lens, and the third lens is a lens with a concave surface facing the object law. Feature 5 (“The lens system according to claim (1).