JPH0545594A - Evf lens - Google Patents

Abstract

PURPOSE:To offer a small-sized optical system which has superior optical performance by suppressing an increase in the overall length of a lens system accompanying enlargement rate reduction as to a lens for an electronic viewfinder(EVF) used as the viewfinder of a video camera. CONSTITUTION:A 1st lens 1 which has negative refracting power and is in a right-left symmetrical aspherical surface shape and a 2nd lens 2 which has positive refracting power and is in a right-left symmetrical aspherical surface shape are arranged between a side close to an object surface 4 and an eye point 3; and -1.0<=epsilon1<=0.5 (1) and epsilon2=0.6Xepsilon1-0.3 (2) hold for cone coefficients epsilon1 and epsilon2 showing the aspherical surface shapes of the 1st and 2nd lenses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens for an electronic viewfinder (hereinafter referred to as an EVF lens) suitable for a video camera or the like.

[0002]

2. Description of the Related Art In recent years, with the spread of video cameras, EV
There is a strong demand for smaller and lighter F lenses.

A conventional EVF will now be described with reference to the drawings.
An example of the lens will be described. FIG. 4 shows a structure of a conventional EVF lens, which is composed of one biconvex plastic lens 5 including an aspherical surface between an object plane 6 and an eye point 7.

The conventional EVF lens having the above structure will be described below with reference to FIG.
That is, the lens 5 is installed at a position approximately the focal length of the lens 5 from the display surface of the CRT, liquid crystal or the like, and the image magnified by the lens 5 is observed from the eye point position 7. In this case, simply increasing the magnifying power to shorten the total length of the viewfinder will worsen various aberrations, and if the symmetric object is liquid crystal, there is dot interference, so the magnifying power is optimal. Must be kept to a certain value.

[0005]

However, the conventional configuration with only one lens is not sufficient in terms of lens performance in terms of maintaining an optimum magnification ratio and shortening the overall length and reducing the size. Had a point. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems and provide an EVF lens that reduces the distance between the object plane and the eye point and downsizes the device while maintaining the optimum magnification.

[0006]

In order to achieve the above object, the EVF lens of the present invention has a negative refractive power first lens on the side closer to the object, which has a symmetrical aspherical shape in a sectional view. The second lens having a positive refracting power on the side far from the object has an aspherical shape which is symmetrical in the cross-sectional view, and -1.0≤ε ₁ ≤0.5 (1) ε ₂ = 0.6 × ε ₁ -0.3 (2) (where ε ₁ and ε ₂ are conical coefficients representing the aspherical shapes of the first and second lenses, respectively) are provided so as to satisfy the condition.

[0007]

According to the present invention, the distance between the object and the eye point can be reduced without changing the optimum magnification of the lens system by the above structure.

[0008]

EXAMPLES An EVF lens according to one example of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an EVF lens according to an embodiment of the present invention. In FIG. 1, the first lens 1 on the side closer to the object plane is a lens having a bilaterally symmetric aspherical shape in a sectional view and having a negative refractive power. The second lens 2 on the side far from the object is a lens that has an aspherical shape that is bilaterally symmetric in a sectional view and that has a positive refractive power. Further, r ₁ and r ₂ are the radii of curvature of the surface of the first lens 1 on the object surface side and the surface on the opposite side thereof, and r ₃ and r ₄ are the surface of the second lens 2 on the object surface side and the surface on the opposite side thereof. Radius of curvature of d ₁ ,
d ₂ and d ₃ are the wall thickness between the lens surfaces of the first lens 1, the air gap between the first lens 1 and the second lens 2, and the wall thickness between the lens surfaces of the second lens 2, respectively.

The numerical values of the EVF lens thus constructed are shown in Table 1, and the combinations of ε ₁ and ε ₂ which are conical coefficients representing the aspherical shapes of the first and second lenses are changed. Maximum lateral aberration ΔY and maximum distortion DI
The value of ST is shown in Table 2. The numbers corresponding to the coordinates of the combinations of ε ₁ and ε _{2 in} FIG. 3 are the numbers of the combinations of ε ₁ and ε _{2 in} Table 2.

In the table, n ₁ and n ₂ are d of the first and second lenses.
Refractive indices for lines, v ₁ and v ₂ are d of the first and second lenses
Abbe number for a line.

[0011]

[Table 1]

The object surface is -37.21 mm from the left surface of the first lens
The position and size of the object are 19.3 mm × 13.9 mm.

[0013]

[Table 2]

The EVF lens constructed as described above and having the numerical values shown in Table 1 will be described below with reference to FIGS.
Will be described with reference to. 2 (a), (b), (c)
And (d) show the aberration performance of this example, respectively.

In FIG. 2A, the solid line indicates the d-line, the broken line indicates the F-line, and the alternate long and short dash line indicates the spherical aberration with respect to the c-line.
In FIG. 2B, the solid line shows sagittal field curvature, the broken line shows meridional field curvature, and in FIG. 2D, the solid line shows F-line for d line, and the broken line shows chromatic aberration of magnification for c-line with respect to d line. The first and second lenses operate so that an image of an optimum size can be observed from the eye point. FIG. 2 shows that due to miniaturization, it has good optical performance regardless of using the first and second lenses having strong refractive power.

The aspherical shapes of the first and second lenses are
Ε, which is the conic coefficient₁ And ε ₂ Union that changed the value of
Examine the results in Table 2 corresponding to the coordinate numbers in FIG.
, -1.0≤ε₁ ≤ 0.5 (1) ε₂ = 0.6 x ε₁If the range of the condition is −0.3 (2), the maximum lateral aberration ΔY is 2 dio.
And the maximum distortion DIST exceeds 1%.
First of all, it was found that good image performance can be obtained.

By thus setting the values of ε ₁ and ε ₂ , it is possible to achieve the optimal size and weight reduction as an EVF lens.

As in the above embodiment, the lens material is usually a plastic lens because of the nature of the EVF lens and the processing problem due to the use of an aspherical surface, but the use of other materials such as glass is not hindered. ..

[0019]

As described above, in the EVF lens of the present invention, the first lens having a negative refractive power on the side closer to the object has a symmetrical aspherical shape, and the positive refraction on the side far from the object. The second lens having power has a bilaterally symmetric aspherical shape, and is configured so as to satisfy the above condition between the conic coefficients representing the aspherical shapes of the first and second lenses, respectively. It is possible to obtain an excellent effect that the overall length of the lens portion is short and the size is small, while maintaining an optimum magnification and maintaining good performance.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an AVF lens according to an embodiment of the present invention.

[Figure 2] Similarly, the aberration diagram

[Fig. 3] Similarly, a combination coordinate diagram of the conical coefficients ε ₁ and ε ₂ .

FIG. 4 is a block diagram of a conventional AVF lens.

[Explanation of symbols]

1 1st lens 2 2nd lens r ₁ , r ₂ Object surface side surface of the 1st lens 1 and the curvature radii r ₃ and r _{4 of} the surface on the opposite side and the object surface side surface of the 2nd lens 2 and its opposite Radius of curvature of the side surface d ₁ Thickness between the lens surfaces of the first lens 1 d ₂ Air gap between the first lens 1 and the second lens 2 d ₃ Thickness between the lens surfaces of the second lens 2 3 Object surface 4 eye points

Claims (2)

[Claims] 1. A first lens having a negative refractive power on the side closer to the object has a bilaterally symmetric aspherical shape in a cross-sectional view, and a second lens having a positive refractive power on the side far from the object has a cross-sectional view. It has a symmetrical aspherical shape, and is -1.0 ≤ ε ₁ ≤ 0.5 (1) ε ₂ = 0.6 × ε ₁ -0.3 (2) (where ε ₁ and ε ₂ are respectively 1. An EVF lens configured so as to satisfy the conditions of (1, the conical coefficient representing the aspherical shape of the second lens). 2. The EVF lens according to claim 1, wherein the first and second lenses are made of plastic.