KR100366236B1 - Finder with variable magnifying power - Google Patents

Abstract

PURPOSE: A finder with a variable magnifying power is provided to improve the assemblability by constructing an optical system having a variable 3-power over. CONSTITUTION: An object lens group comprises a first lens(10) having a positive refractive index, a second lens(20) having a negative refractive index, a third lens(30) having a positive refractive index, and fourth lens(40) having a positive refractive index. An eye lens group is comprised of a fifth lens(50) having a positive refractive index. The first lens(10) functions as a cover glass of a finder. The second lens(20) and the third lens(30) are installed so as to be moved for adjusting a magnifying power of an image. The third lens(30) moves between the second lens(20) and the fourth lens(40) to adjust the magnifying power. An image passing the first lens(10) is formed as an inverted real image around the fourth lens(40).

Description

Variable Magnification Finder

The present invention relates to a variable magnification finder, and more particularly, to a variable magnification finder suitable for a camera having a zoom function, a video camera, and the like.

In general, optical devices such as a camera and a video camera having a zoom function is a device that can enlarge or reduce the target object without moving the position of the optical device. With this optical apparatus, in order to visually check the changing magnification at the time of imaging, the finder integrated with the optical apparatus needs to change its magnification in accordance with the magnification magnified through the lens. Inverted Galilean or Albanian finders were widely used for this purpose.

An inverted Galilean or Albanian finder is a virtual finder. These finders have the advantage that the viewfinder can be made relatively wider and the size of the finder can be miniaturized because there is no need for an upright prism, but the size of the objective lens group located on the object side becomes larger, the boundary of the field frame is unclear, There is a disadvantage that the field of view changes depending on the position of the eye. In addition, the addition of the panorama function, the miniaturization of the camera, and the wide angle of the photographing lens are required, thereby limiting the use of the virtual image finder.

In order to overcome the shortcomings of the virtual image optical system, a practical finder has been disclosed in Japanese Unexamined Patent Publication Nos. Hei 6-102454 and U.S. Patent Nos. 4,842,395 and 5,086,353.

The finder disclosed through Japanese Unexamined Patent Publication No. Hei 6-102454 among the disclosed variable magnification finders is a variable magnification finder having a magnification variable ratio of 2.0 times or less, and the refractive power of the second lens group constituting the objective lens is excessively large, causing distortion aberration and the like. It is difficult to vary at a higher magnification of 2.0 times or more.

1 and 2 are schematic diagrams showing a conventional finder optical system disclosed through US Pat. No. 4,842,395.

The first lens group 1 having negative refractive power, the second lens group 2 having positive refractive power, and the third lens group 3 are sequentially provided from the object side toward the eye position. An eyepiece group 6 having a refractive power of? And having a positive refractive power is provided on the rear slope surface. The second lens group 2 moves in the direction of the arrow in order to enlarge or reduce the object image incident through the first lens group 1 through the eyepiece group 6. The first lens group 1 and the first image are formed such that an object image passing through the first lens group 1 and the second lens group 2 is formed as an inverted chamber image in front of the incident surface of the third lens group 3. The two lens group 2 has a positive refractive power as a whole. In addition, in order to correct aberration caused by the movement of the second lens group 2, the first lens group 1 also moves in the direction indicated by the arrow along with the second lens group. The object image on the inverted chamber that has passed through the third lens group 3 is converted into the upright chamber image through Polo prism (5). This sizing image is brought into the field of view through the eyepiece group 6. Of course, the size range of an object entering the field of view changes in proportion to the size range of the object image photographed through the camera.

In the first lens group 1 and the second lens group 2, the ratio of the refractive power between the plane on which the object image is incident and the plane on which the image is reflected is contained within a predetermined range, and the image distortion and the group of object images such as halo and halo ( halo) does not occur.

The variable magnification finder disclosed through U.S. Patent No. 5,086,353 is also a variable magnification finder having a structure similar to that of U.S. Patent No. 4,842,395 cited above.

The variable magnification finder thus constructed has a structure in which the magnification is adjusted by moving the first lens group having a maximum magnification ratio of about 2.0 times and having positive refractive power. In this way, a cover glass separate from the first lens group is required due to the flow of the first lens group. In addition, since the field frame must be positioned at an object position formed through the objective lens group in order to clearly cut the field of view, the object image needs to be imaged once inside the finder. In this case, the structure of the finder becomes complicated and its size becomes large.

In addition, it is possible to increase the magnification ratio by three times or more by lengthening the focal length of the objective lens or shortening the focal length of the eyepiece. The case is limited because of the difficulty of mechanical assembly.

Accordingly, an object of the present invention is to provide a real-type magnification-type finder having a high variable magnification ratio having a variable magnification ratio of 3 times or more in a simple lens configuration.

The present invention to achieve the above object,

From the object side, the first lens group having positive refractive power, which is fixed and the object surface is concave or planar, the second lens group being movable and having negative refractive power, and movable A third lens group having a positive refractive power, a fourth lens group fixed and having a positive refractive power, and an objective lens group having an overall positive refractive power,

An eyepiece, which is a fifth lens group having a positive refractive power, is provided behind the objective lens group.

In the present invention,

Focal length of the first lens group ( ) And focal length of the objective lens group at a wide-angle end to ensure a wide angle of view ( ) Ratio of 0 < Of It is preferable to satisfy the conditional expression of <0.25,

Focal length of the second lens group ( ), And the focal length of the objective lens group at the telephoto end ( ) Ratio of -0.70 < Of It is preferable to satisfy the conditional formula of <-0.35, and also,

Focal length of the second lens group ( ) And a focal length of the third lens group ( ) Ratio of -1.10 < Of It is preferable to satisfy the conditional formula of <-0.65.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 to 6 are schematic views showing an embodiment of the variable-scaling finder according to the present invention.

This magnification-type finder optical system is composed of an objective lens group having positive refractive power from the object side and an eyepiece group having positive refractive power. The objective lens group includes a first lens group 10 having positive refractive power, a second lens group 20 having negative refractive power, and a third lens group 30 having positive refractive power. And a fourth lens group 40, wherein the eyepiece group consists of a fifth lens group 50 having positive refractive power.

The first lens group 10 is a lens group having positive refractive power whose object side is concave or planar and its opposite surface is convex, and is fixed to serve as a cover glass of the finder. By reducing the refractive power of the first lens group 10 as much as possible, the burden of refractive power of the second lens group 20 having negative refractive power is reduced so that aberrations such as spherical aberration occur less.

The second lens group 20 and the third lens group 30 are movably installed to adjust the magnification of the object image observed through the eyepiece group. The third lens group 30 changes the magnification while moving between the second lens group 20 and the fourth lens group 40. This change in magnification caused by the change in magnification is compensated for by moving the second lens group 20. In addition, the lens group between the first lens group 10 and the fourth lens group 40 is provided with a lens group having at least one aspherical surface to correct the lens aberration.

The object image passing through the first lens group 10 is formed as an inverted chamber image around the fourth lens group 40, and is disposed between the fourth lens group 40 and the fifth lens group 50. The optical image, such as a prism 60, which converts the image of the image formed into an image to an upright image, can be visually confirmed by the eyepiece through the eyepiece lens.

FIG. 3 shows an embodiment of the above-mentioned finder, and consists of the lens group as mentioned above, and the data is shown in Table 1.

In Table 1, the symbol ω is a half angle of view indicating the half of the angle between the lens center, D is the thickness of the lens, or the width between the lenses, R is the diameter of the lens, and Nd is the lens refractive index on the thickness D line. And v is the Abbe's number of the lens. In addition, K represents a conic constant and A represents an aspherical coefficient. Here, the subscripts attached to the cited symbols are surface numbers indicating the surface of the lens.

4 is a lens arrangement diagram for explaining the change in magnification of FIG. 3, (A) is a lens arrangement diagram showing a wide-angle end, (B) is a lens configuration diagram showing a center end, and (C) a telephoto end.

As shown in (A), the wide angle of view can secure the widest field of view with 2ω = 48.9 °, and as shown in (B), the angle of view is as 2ω = 25.1 °. An object image with a magnification of approximately 1 can be obtained.In the case of a telephoto fabric with a lens as shown in (c), the angle of view is 2ω = 15.1 ° to provide the narrowest angle of view to obtain an object image with the largest magnification. Can be.

5 and 6 show examples 2 and 3 of the variable-scaling finder according to the present invention, and have numerical data as shown in Tables 2 and 3, respectively.

Here, reference numerals are the same as described in Example 1.

(A) to (b) of FIG. 7 (a) to (a) of FIG. 8 show lens aberration diagrams of spherical aberration, astigmatism, distortion, etc. of each embodiment, and (a) of the angular plane at the wide-angle end. (A) shows lens aberration at the telephoto end, and lens aberration at the center end is omitted.

Focal length of the first lens group 10 ( ) And the focal length of the objective lens group at the wide-angle end ( ) Ratio of 0 < Of It is preferable to satisfy the conditional expression of the conditional expression of <0.25. If the ratio exceeds the upper limit of the conditional expression, the refractive power of the first lens group 10 is increased, and thus, the refractive power of the second lens group 20 is also increased. As a result, the degree of astigmatism and distortion aberration increases. In the case where the lower limit of the conditional expression is exceeded, the first lens group 10 has negative refractive power, so that the optical system becomes long as a whole and it is difficult to miniaturize.

Focal length of the second lens group 20 ( ) And focal length of the objective lens group at the telephoto end ( ) Ratio of -0.70 < Of It is preferable to satisfy the conditional formula of <-0.35. If the upper limit of the conditional expression is exceeded, the refractive power of the second lens group 20 and the refractive power of the third lens group 30 become smaller, and the overall shape thereof becomes longer, making it difficult to miniaturize. If exceeded, the refractive power of the second lens group 20 and the refractive power of the third lens group 30 become large, resulting in large aberration.

Focal length of the second lens group 20 ( ) And the ratio of the focal length f3 of the third lens group 30 to -1.10 < Of It is preferable to satisfy the conditional formula of <-0.65. If the upper limit of the conditional expression is exceeded, the refractive power of the second lens group 20 is increased, so that aberrations such as distortion are generated, and accordingly, the refractive power of the other lens group has to be increased. In addition, when the conditional expression exceeds the lower limit, the refractive power of the second lens group 20 becomes too small, which is somewhat advantageous for aberration correction, but the amount of movement becomes large, so that the magnification variable ratio cannot be increased in a predetermined space. have.

Therefore, it is preferable to design the system so as to satisfy the above three conditional expressions, and according to the numerical data of the optical system shown through Example 1 to Example 3 of the present invention. , , , , The mutual ratios are shown in Table 4.

Each lens group uses plastic material that is cheaper than glass in terms of price, and in particular, the entire lens group uses only one type of plastic material called PMMA to simplify production. The chromatic aberration correction problem caused by the use of a single material was corrected by properly selecting the refractive power of each lens.

The aspherical shape shown through each embodiment can be expressed by the following equation.

here,

X: distance from the vertex of the lens to the optical axis direction

y: distance in the direction perpendicular to the optical axis

C: Inverse of the radius of curvature at the vertex of the lens

K: Conic Constant

A ₄ , A ₆ , A ₈ , A ₁₀ : Aspheric coefficient

Accordingly, the variable magnification finder according to the present invention is a very useful invention that provides high precision magnification control means while improving assembly performance, reducing cost, and miniaturization.

Table 1 <Example 1>

Table 2 <Example 2>

Table 3 <Example 3>

Aspheric coefficient of the R10 plane

Table 4

1 is a schematic cross-sectional view showing a conventional variable view finder.

2 is a schematic diagram showing a path on an object incident through a conventional variable view finder.

3 is a schematic cross-sectional view showing Embodiment 1 of a variable-scaling finder of the present invention.

(A), (b) of FIG. 4 are schematic diagrams showing the case of wide-angle end, center end, and telephoto end of the variable magnification finder of Example 1 shown in FIG.

5 and 6 are schematic cross-sectional views showing Embodiments 2 and 3 of the variable-scaling finder of the present invention.

7A through 9B are aberration diagrams showing the aberrations of the optical system of the variable-scaling finder of the present invention shown in Example 1 through Example 3. FIG.

Claims (8)

From the object side, a first lens group having positive refractive power, which is fixed and concave or planar, and a second lens group that is movable and has negative refractive power, is movable and defined An objective lens group including the third lens group having a refractive power and the fourth lens group fixed and having a positive refractive power as a whole to have a positive refractive power; And an eyepiece group, which is a fifth lens group having a positive refractive power, behind the objective lens group. The method of claim 1, The third lens group is movably installed to change the size of an image observed through the eyepiece, and the second lens group compensates for the change in intensity caused by the movement of the third lens group. Variable magnification finder, characterized in that installed so as to be movable. The method of claim 1, Focal length of the first lens group ( ) And focal length of the objective lens group at a wide-angle end to ensure a wide angle of view ( The variable magnification finder characterized by the following conditional expression. 0 < Of <0.25 The method according to claim 1 or 3, Focal length of the second lens group ( ), And the focal length of the objective lens group at the telephoto end ( The variable magnification finder characterized by the following conditional expression. -0.70 < Of <-0.35 The method according to claim 1 or 3, Focal length of the second lens group ( ) And a focal length of the third lens group ( The variable magnification finder characterized by the following conditional expression. -1.10 < Of <-0.65 The method according to claim 1 or 3, The variable magnification finder of claim 1, wherein each lens group from the first lens group to the fifth lens group is made of a plastic material. The method of claim 1, And the lens group between the first lens group and the fourth lens group comprises a lens group having at least one aspherical surface. The method of claim 1, And said fourth lens group has a convex surface that has a stronger object side than an image side.