KR20000059525A - Optical system having a high magnification viewfinder lens - Google Patents

Abstract

end. TECHNICAL FIELD This invention relates to a high magnification viewfinder optical system.

I. SUMMARY OF THE INVENTION An object of the present invention is to provide an optical system having a viewfinder lens capable of attempt adjustment from -5D to + 1.5D with a minimum lens moving distance in a camcorder or broadcast camera employing an LCD.

All. SUMMARY OF THE INVENTION An optical system having a high magnification viewfinder lens, comprising: a first lens having a negative refractive power designed as an aspherical surface disposed on a screen side, and a positively shifted spaced apart from the first lens by a predetermined distance; And a second lens having refractive power.

la. Important uses of the invention: Can be used for camcorders and broadcast cameras.

Description

OPTICAL SYSTEM HAVING A HIGH MAGNIFICATION VIEWFINDER LENS}

The present invention relates to a viewfinder of a camcorder or a broadcast camera employing a liquid crystal display (LCD), and in particular, it is possible to adjust the diopter (-5D to + 1.5D) with a minimum lens stroke. An optical system having a high magnification viewfinder lens to provide a bright image.

Generally, one lens is used for the viewfinder of a camcorder and a broadcast camera employing an LCD. Accordingly, there is a problem in that chromatic aberration is bad due to a distortion aberration indicating an image distortion degree and a refractive index difference according to a wavelength of a lens. In addition, since a single lens is used to adjust the distance from -5D to + 1.5D (Diopter), at least 80 mm or more lens moving distance is required, and thus, there is a limitation in slimming the mechanism of the barrel.

Accordingly, an object of the present invention is to provide an optical system having a high magnification viewfinder lens capable of attempt adjustment from -5D to + 1.5D with a minimum lens moving distance in a camcorder or broadcast camera employing an LCD.

Still another object of the present invention is to provide an optical system having a high magnification viewfinder lens capable of slimming the viewfinder of a camcorder or a broadcast camera employing an LCD and reducing the viewfinder weight.

The present invention for achieving the above object is an optical system having a high magnification viewfinder lens,

A first lens having a negative refractive power designed as an aspherical surface disposed on the screen;

And a second lens having a positive refractive power that moves at a predetermined interval apart from the first lens.

1 is a lens configuration and layout of a high magnification viewfinder optical system according to an embodiment of the invention.

2A and 2B illustrate a sag in the case of adopting a spherical lens (FIG. 2A) and an aspherical lens (FIG. 2B) according to an embodiment of the present invention. Output characteristic diagram.

3A and 3B are aberration diagrams when the diopters of the lenses according to the embodiment of the present invention are -5 diopters.

4A and 4B are aberration diagrams when the diopters of the lenses according to the embodiment of the present invention are +1.5 diopters.

Hereinafter, an operation according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 illustrates a lens configuration layout of a high magnification viewfinder optical system according to an embodiment of the present invention.

Hereinafter, referring to FIG. 1, a lens configuration of a high magnification viewfinder optical system according to an exemplary embodiment of the present invention will be described. The second lens L2 having a positive refractive power is positioned at a position spaced apart from the first lens L1 by an eye point. The second lens L2 moves along the optical axis, and the second lens L2 is disposed to have a minimum moving distance, preferably 2 mm. By allowing the second lens L2 to be movable, diopter adjustment according to a user's eye difference is possible. On the other hand, the first lens (L1) and the second lens (L2) is made of a plastic aspherical lens to achieve an effect that can be reduced in weight and cost. In addition, the first lens L1 replaces the role of the aperture without using a separate aperture, thereby simplifying the mechanism structure of the barrel.

2A and 2B illustrate a sag in the case of adopting a spherical lens and an aspherical lens according to an embodiment of the present invention. The calculation characteristic diagram is shown.

2A and 2B, first, when the height at the optical axis is Y at the plane where the curvature on the optical axis of the reference sphere is C (= 1 / R) at the aspherical surface, sag Xa at the aspherical surface and sag Xo at the spherical surface In comparison, Equations 1 and 2 are shown.

Aspheric Lens:

In the above equations, C represents curvature, R represents a radius of the lens, Y represents a height, K represents a conic constant, and AD, AE, AF, and AG represent aspherical coefficients, respectively.

3A and 3B illustrate aberration diagrams when the diopters of the lenses according to the embodiment of the present invention are -5 diopters, and FIGS. 4A and 4B illustrate the diopters of +1.5 diopters according to the embodiment of the present invention. It shows the aberration diagram when.

Hereinafter, the characteristics of an optical system having a high magnification viewfinder lens according to an embodiment of the present invention will be described with reference to FIGS. 1 and 3A, 3B, and 4A and 4B.

First, the high magnification viewfinder lens according to the embodiment of the present invention is composed of two lenses L1 and L2 as shown in FIG. 1, in which the second lens L2 is moved so that the diopter according to the individual eye difference of the user The adjustment amount can be varied as shown in Table 1 below. The numerical values in Table 1 below are the order of planes in the order of left to right, the radius of curvature (Radius), the distance from the optical axis movement path (lens center) to the next lens plane, and the refractive index of the medium located on the right side of each lens plane ) And variance. That is, the radius of curvature at lens surface 2 is 14.02605, the center distance from lens surfaces 2 to 3 is 5.7 mm, and the refractive index and dispersion at lens surface 2 are 1.49 and 57.9, respectively. And if the data on each lens surface is defined as follows, sag Xa in the aspherical lens will be easily calculated by Equation 1 above.

Lens surface Radius of curvature Center interval Refractive index Dispersion Remarks 2 14.02605 5.7 1.49 57.9 4 -14.95315 1.5 to 3.5 -5D to _1.5D 6 -35.21824 2.0 1.585 30.3 8 14.78828 21.5

Aspheric data

→ lens side 2:

K: -1.845262,

AD: 0.342127E-04, AE: 0.195541E-06, AF:-. 543854E-08, AG:-. 186936E-10

→ lens face 3:

K: -0.095706,

AD: 0.191467E-03, AE:-. 106185E-05, AF: 0.418432E-09, AG: 0.234422E-11

→ lens side 4:

K: -14.818065,

AD: 0.654014E-04, AE: 0.133771E-05, AF:-. 194960E-07, AG:-. 131409E-10

→ lens surface 5:

K: -0.698488,

AD: 0.128871E-03, AE:-. 338248E-05, AF: 0.174280E-06, AG:-. 222583E-08

3A, 3B, and 4A and 4B illustrate numerical values of lens data when the diopters of the lens according to the embodiment of the present invention are -5 diopters and 1.5 diopters. In FIGS. 3A to 4B, the meridional fan and the sagital fan are respectively illustrated according to three colors in the fields 0.0 (on axis), 0.5, 0.7, and 1.0, respectively, meridian top surface curvature (T) and nodular top surface curvature (S) and white powder. DISTORTION is shown. The three colors illustrate red, yellow, and blue, and red is shown as a broken line, yellow is a solid line, and blue is a dashed line.

On the other hand, the distortion in the optical system is minimal when the image distance and the object distance are similar. However, in the general optical system, the image distance and the object distance are different, so that the distortion aberration is corrected by adjusting the shape of the lens, the arrangement of the refractive power, and the position of the aperture. Accordingly, in the exemplary embodiment of the present invention, the amount of distortion is canceled by canceling the amount of positive distortion caused by the first lens L1 having negative refractive power and the amount of negative distortion caused by the second lens L2 having positive refractive power. Can be reduced.

As described above, the present invention cancels the amount of distortion by canceling the amount of positive distortion caused by the first lens L1 having negative refractive power and the amount of negative distortion caused by the second lens L2 having positive refractive power. There is an advantage that can be reduced, since the moving distance of the lens for the adjustment can be maintained at 2mm, the mechanism structure of the barrel can be made slim, and by introducing a plastic aspherical surface to the lens has the advantage of reducing the production cost.

Claims (7)

In an optical system having a high magnification viewfinder lens, A first lens having a negative refractive power designed as an aspherical surface disposed on the screen; And a high magnification viewfinder lens comprising a second lens having a positive refractive power moving at a predetermined interval apart from the first lens. 2. The method of claim 1, wherein the focal length of the optical system is f, the focal length of the first lens is f1, the focal length of the second lens is f2, a back focal length is B, and at the first lens surface. When the distance to the last lens surface is T and the sag of the reference sphere is Xa on the aspherical surface and the sag by the aspheric surface is Xo, And the back focal length (B) divided by the focal length (f) of the optical system is equal to or greater than 0.6. The optical system having a high magnification viewfinder lens according to claim 2, wherein the value obtained by subtracting the sag Xo by the aspherical surface from the sag Xa of the reference spherical surface has a negative value. The optical lens having a high magnification viewfinder lens according to claim 2, wherein a value obtained by dividing the distance T from the first lens surface to the last lens surface by the focal length f of the optical system has a value of 1.5 or less. system. The high magnification viewfinder of claim 2, wherein the absolute value has a larger value in order of focal length f1 of the first lens, focal length f of the optical system, and f2 of the second lens. Optical system with a lens. 6. The high magnification viewfinder lens according to any one of claims 1 to 5, wherein the second lens moves along an optical axis within a range of 2 mm to enable diopter adjustment according to a user's eye difference. Optical system. The method of claim 1, wherein the first lens is made of a plastic material having a relatively high refractive index and low dispersion, and the second lens is made of a plastic material having a relatively low refractive index and large dispersion. An optical system having a high magnification viewfinder lens.