JPS6113567B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an eye lens in a visual optical system. A typical visual viewing optical system is a finder optical system of a single-lens reflex camera, which basically has a configuration in which a real image on an imaging plane is observed through an eye lens. Usually, a field lens is often disposed at or near the imaging plane, and an eyepiece made of such a field lens and an eye lens is called a Kernel eyepiece. In actual configurations, it is also common practice to replace the field lens with a Fresnel lens that has the effect of a field lens, or a prism that has been given a curvature to have a lens effect. . The eye lens in such a Kernel type eyepiece system, except for special finder optical systems, is a simple lens using a single lens made of optical glass or a cemented lens made by cementing two optical glass lenses. The structure is in place. The structure using a single lens is the simplest, but since there is a problem with chromatic aberration in particular, a cemented lens is often used. SUMMARY OF THE INVENTION An object of the present invention is to provide an eye lens of a visual optical system that is lower in cost than a conventional eye lens made of a cemented lens and has no problems in terms of aberrations. The eye lens according to the present invention is characterized in that it is composed of two plastic lenses, a positive and a negative lens, separated by a narrow air gap in the order of incidence of light, and that it satisfies the following conditions. (1) ｜r ₃ ｜＞｜r ₄ ｜ (2) −0.01fe＜｜r ₄ ｜−｜r ₅ ｜＜0.02fe (3) 0.001fe＜d ₄ ＜0.01fe (4) ν ₂ ＞50.0, ν ₃ ＞38.0 However, r ₃ , r ₄ , r ₅ , r ₆ are the radius of curvature of each surface of the eye lens in the order of incidence of light, d ₄ is the air distance between the positive lens and the negative lens in the eye lens, and fe is the air distance between the positive and negative lenses in the eye lens. The composite focal lengths of the eye lens, ν ₂ and ν ₃ , are the Abbe numbers of the plastic materials of the positive and negative lenses in the eye lens, respectively. In the above, conditional expression (1) is a conditional expression for reducing spherical aberration, field curvature, and angular aberration. If this relationship is reversed, comatic aberration will become especially large, and the image will flow due to shaking of the eye, making the lens unsuitable as a finder. Conditional expression (2) is to keep angular aberration and comatic aberration small, and if this conditional expression is not satisfied, even if conditional expression (1) is satisfied, angular aberration cannot be sufficiently corrected, and , comatic aberration also increases. Conditional expression (3) regulates the air distance between the positive lens and the negative lens, and is a condition for reducing angular aberration and comatic aberration and improving image surface characteristics. By setting the air gap to 0.001 fe or more, independent degrees of freedom are given to the surfaces r ₄ and r ₅ that sandwich the air gap. Furthermore, if the air spacing is 0.01 fe or more, coma aberration will increase and have the opposite effect. Conditional expression (4) specifies the Abbe number of the plastic material used for the positive lens and the negative lens, especially for correcting angular aberration. If the positive lens is made of plastic with an Atsube number of 50 or less, and the negative lens is made of plastic with an Atsube number of 38 or more, the radius of curvature of the surfaces r ₄ and r ₅ that sandwich the air gap must be made small, otherwise the achromatic effect will occur. However, this causes the occurrence of coma aberration to increase. Therefore, conditional expression (4)
The plastic material must be selected accordingly. As plastic materials that satisfy conditional expression (4), acrylic resins such as polymethyl methacrylate (about 58) can be used for positive lenses, and styrene resins such as styrene resins can be used for negative lenses. Polystyrene (Atsube number 31
degree), polycarbonate (about 35 degrees),
Alternatively, a copolymer of an acrylic resin and a styrene resin, for example, a copolymer of styrene acrylonitrile (Abbe number: about 35) can be used. The present invention will be explained below with reference to the drawings. FIG. 1 shows a conceptual diagram of the basic form of a Kernel type eyepiece lens system in which the eye lens of the present invention is used. I is an image plane, and L _F is a field lens.
The field lens L _F is not limited to the illustrated arrangement, and may be arranged in front of the image plane I when viewed from the light incident direction, or may be arranged on the image plane. Furthermore, instead of a field lens, a Fresnel lens or a prism with a portion of curvature may be used, and this also applies to the examples described below. L _E
is the eye lens of the present invention, _L1 is a plastic positive lens, and _L2 is a plastic negative lens. Note that E is the observer's eye. FIG. 2 shows a conceptual diagram of a visual optical system using the eye lens of the present invention. The image plane I is
It is created by an objective lens L ₀ via a prism P and a filter F. The image plane I created in this way is observed by the field lens L _F and the eye lens L _E of the present invention. FIG. 3 shows a conceptual diagram of a finder optical system for a single-lens reflex camera using the eye lens of the present invention. Image plane I is the objective lens
L ₀ is created on a Fresnel lens that functions as a focusing plate via a mirror. The Fresnel lens and condenser lens together form a field lens L _F. P is a pentaprism, L _E is an eye lens of the present invention. FIG. 4 shows a conceptual diagram of an equivalent optical system from the field lens L _F to the eye lens L _E in FIG. 3. Next, specific examples of the present invention will be shown. Examples 1, 2, and 3 are manufactured as optical systems whose conceptual diagram is shown in FIG. Example 1

【table】 Example 2

【table】

【table】 Example 3

[Table] The aberration diagrams of Examples 1, 2, and 3 are shown in the fifth and
Shown in Figures 6 and 7. Examples 4 and 5 shown below were made as visual optical systems as shown in FIG. Note that in the fifth embodiment, the configuration from the objective lens L ₀ to the filter F is the same as that in the fourth embodiment, and is therefore omitted. Example 4

【table】

【table】 Example 5

[Table] Aberration diagrams of Examples 4 and 5 are shown in FIGS. 8 and 9, respectively. Examples 6 to 10 below were made as equivalent optical systems to the finder optical system of the single-lens reflex camera shown in FIG. Example 6

【table】 Example 7

【table】

【table】 Example 8

【table】 Example 9

【table】 Example 10

【table】

[Table] Aberration diagrams of Examples 6 to 10 are shown in numbers 10 to 14, respectively.
As shown in the figure. Next, an example will be shown in which the optical system shown in FIG. 4 is made and in which an aspherical surface is introduced into a part of the surface of the eye lens. Example 11

[Table] When using aspheric surfaces for r ₄ and r ₅ as described above, it is desirable that |ε ₄ −ε ₅ |<0.2,
On the other hand, when |ε ₄ −ε ₅ |>0.2, the coma aberration becomes large and is no longer suitable for practical use. Example 12

【table】

[Table] The aberration diagrams of Examples 11 and 12 are shown in the 15th and 1st tables, respectively.
It is shown in Figure 6. Note that FIG. 17 illustrates the eye lens in the above-mentioned Example 6. When manufacturing an actual eye lens, the features of the present invention can be realized by integrally molding a protrusion for setting an air gap as shown by S in FIG. 17 on the peripheral edge of the positive lens or the negative lens. A narrow air gap can be easily set, and the positive lens and negative lens can be handled as a whole like a single cemented lens during assembly. As is clear from the above, the present invention has positive and negative two
Since it is constructed using two plastic lenses, which are arranged with a narrow air gap between them without being cemented together, and which satisfies certain conditions, the manufacturing cost is extremely low, and in terms of aberration performance. This makes it possible to provide eye lenses that are comparable to those of other manufacturers. In addition, since the eye lens of the present invention is composed of a plastic lens, the air gap setting protrusion can be easily integrally molded with at least one lens, and in this case, the narrow It is suitable for setting air spacing. Furthermore, the two positive and negative lenses can be handled as a single cemented lens during assembly.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the basic form of a Kernel eyepiece system using the eye lens of the present invention, Fig. 2 is a conceptual diagram of an ocular viewing optical system using the eye lens of the present invention, and Fig. 3 is a conceptual diagram of the basic form of a Kernel eyepiece system using the eye lens of the present invention. A conceptual diagram of a viewfinder optical system for a single-lens reflex camera using the eye lens of the invention, FIG. 4 is a conceptual diagram of an equivalent optical system of the main part in FIG. 3, and FIGS. Aberration diagrams of Examples 1 to 12 and FIG. 17 are lens configuration diagrams of the eye lens in Example 6. L _E ...Eye lens, _L1 ...Positive lens, _L2 ...
Negative lens, d ₄ ...Air spacing, S...Protrusion for setting air spacing.

Claims (1)

[Claims] 1. An eye viewing optical system comprising only two single plastic lenses, positive and negative, separated by a narrow air gap in the order of incidence of light, and satisfying the following conditions. Lens: ｜r ₃ ｜＞｜r ₄ ｜ −0.01fe＜｜r ₄ ｜−｜r ₅ ｜＜0.02fe 0.001fe＜d ₄ ＜0.01fe ν ₂ ＞50.0, ν ₃ ＜38.0 However, r ₃ , r ₄ , _r5 , _r6 are the radius of curvature of each surface of the eye lens in the order of incidence of light, _d4 is the air distance between the positive lens and negative lens in the eye lens, fe is the combined focal length of the eye lens, _ν2 , ν ₃ is the Abbe number of the plastic material of the positive lens and the negative lens in the eye lens, respectively. 2. The eye lens according to claim 1, wherein an air gap setting protrusion is integrally molded on at least one of the positive lens and the negative lens.