Patent Grant
7903343
The present invention relates to a zoom eyepiece lens system.
A zoom eyepiece lens system securing an eye-relief, and correcting various aberrations has been known (for example, see Japanese Patent Application Laid-Open No. 9-080326).
However, the conventional zoom eyepiece lens system has problems that the eye-relief cannot be sufficiently secured and correction of aberrations is not sufficient yet.
The present invention is made in view of the above-described problems, and has an object to provide a zoom eyepiece lens system having high optical performance with correcting various aberrations excellently, and securing a sufficient eye-relief.
In order to solve the problems, the present invention provides a zoom eyepiece lens system comprising, in order from an observation eye (eyepoint) side: a first lens group having positive refractive power; a second lens group having positive refractive power; and a third lens group having negative refractive power; upon zooming from a low magnification end state to a high magnification end state, the second lens group and the third lens group moving along an optical axis in opposite directions with each other, the second lens group including, in order from the observation eye side, a first lens having negative refractive power, a second lens having positive refractive power, and a third lens having positive refractive power, and at least one aspherical surface being formed on the third lens.
In the aspect of the present invention, it is preferable that the following conditional expression is satisfied:
|re|≦|ro|
where re denotes a radius of curvature of the reference sphere of the observation eye side of the third lens composing the second lens group, and ro denotes a radius of curvature of the reference sphere of an object side of the third lens composing the second lens group.
In the aspect of the present invention, it is preferable that when the aspherical surface in the third lens composing the second lens group is expressed by the following expression:
x=cy2/{1+(1−kc2y2)1/2}+A4y4+A6y6+A8y8+. . .
where y denotes a vertical height from an optical axis, x denotes a distance along the optical axis from a tangent surface on the vertex of the aspherical surface to the aspherical surface at the height y, c denotes a radius of curvature of a reference sphere, k denotes a conical coefficient, and An denotes an aspherical coefficient of n-th order (where n=4, 6, 8, . . . ), the conical coefficient k satisfies the following conditional expression:
k≦0.
With constructing a zoom eyepiece lens system according to the present invention as described above, it becomes possible to provide a zoom eyepiece lens system having high optical performance with excellently correcting various aberrations and securing a sufficient eye-relief.
A preferred embodiment of the present invention is explained below with reference to accompanying drawings. A lens construction of a zoom eyepiece lens system according to the present invention is explained with reference to
In the zoom eyepiece lens system EL, the second lens group G2 is composed of, in order from the eyepoint EP side, a first lens (negative meniscus lens L3 in
Then, conditions for constructing the zoom eyepiece lens system EL are explained. The zoom eyepiece lens system EL is constructed with satisfying the following conditional expression (1):
|re|≦|ro| (1)
where re denotes a radius of curvature of a reference sphere of the eyepoint EP side surface (the seventh surface in
Conditional expression (1) defines a basic shape of the third lens (aspherical lens) L5. When the third lens L5 does not satisfy conditional expression (1), it becomes difficult to secure the eye-relief, to excellently correct distortion, and to balance the other aberrations.
Such an aspherical surface is expressed by the aspherical expression (a) shown below. In the aspherical expression (a), y denotes a vertical height from the optical axis, x denotes a distance along the optical axis from the tangent surface at the vertex of the aspherical surface to the aspherical surface at the vertical height y from the optical axis, c denotes a radius of curvature of a reference sphere, k denotes a conical coefficient, and An denotes an aspherical coefficient of n-th order (here n=4, 6, 8, . . . ):
x=cy2/{1+(1−kc2y2)1/2}+A4y4+A6y6+A8y8+. . . (a).
In the zoom eyepiece lens system EL, a conical coefficient k, which is shown in the aspherical expression (a), of an aspherical surface formed on a surface of the third lens L5 composing the second lens group G2 satisfies the following conditional expression (2):
k≦0 (2).
Conditional expression (2) is for forming the aspherical surface formed on the third lens L5 on the basis of a hyperboloid. When the value exceeds the upper limit of conditional expression (2), the effect of the aspherical surface becomes insufficient, so that it becomes difficult to realize a long eye-relief and to excellently correct distortion. In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (2) to −10. In the aspherical surface of the third lens L5, the conical coefficient k in the aspherical expression (a) is preferably larger than −10. When it falls below −10, distortion becomes overcorrection.
Four examples according to the present invention are explained with reference to accompanying drawings. Incidentally, in each example, although the aspherical surface formed on the third lens L5 composing the second lens group G2 is expressed by the aspherical expression (a), aspherical coefficients An (n=4, 6, 8, . . . ) are all zero. It is a matter of course that the aspherical coefficient An may have a value other than zero.
Various values associated with Example 1 are listed in Table 1. In Table 1, f denotes a focal length of the lens system, F.NO denotes an f-number, f1 denotes a focal length of the first lens group G1, f2 denotes a focal length of the second lens group G2, and f3 denotes a focal length of the third lens group G3. The first column shows a lens surface number counted along a light proceeding direction from the eyepoint EP, the second column shows a radius of curvature of each lens surface, the third column shows a surface distance from each optical surface to the next optical surface along the optical axis, the fourth column shows a refractive index at d-line (λ=587.6 nm), and the fifth column shows an Abbe number. An aspherical surface expressed by the aspherical expression (a) is shown by attaching “*” to the right side of the surface number. A radius of curvature equal to 0.000 denotes a plane surface, and the refractive index of the air 1.00000 is omitted. In respective tables for various values, “mm” is generally used for the unit of length such as the focal length f, f1 through f3, the radius of curvature and the distance to the next lens surface. However, since similar optical performance can be obtained by an optical system proportionally enlarged or reduced its dimension, the unit is not necessarily to be limited to “mm”, and any other suitable unit can be used. The explanation of reference symbols and tables is the same in the other Examples.
In Table 1, “Low Mag. End” denotes a low magnification end state, “High Mag. End” denotes a high magnification end state, 2ω denotes an angle of view, IH denotes an image height, TL denotes a total lens length. In [Lens Data], “i” denotes a surface number, “r” denotes a radius of curvature, “d” denotes a distance to the next optical surface, “nd” denotes a refractive index at d-line, and “ν” denotes an Abbe number. Reference symbols are the same as the other Examples.
In the zoom eyepiece lens system EL1, upon zooming, the second lens group G2 and the third lens group G3 move along the optical axis in opposite directions with each other, and the field stop FS also moves along the optical axis independently. Accordingly, a distance d3 along the optical axis between the first lens group G1 and the second lens group G2, a distance d8 along the optical axis between the second lens group G2 and the field stop FS, a distance d9 along the optical axis between the field stop FS and the third lens group G3, and the back focal length Bf are varied upon zooming. The eye-relief ER, and variable distances with respect to each focal length of the system in the low magnification end state and the high magnification end state are shown in Table 2. Here, the eye-relief ER is a distance along the optical axis between the eyepoint EP and the first surface.
In the following Table 3, values for respective conditional expressions according to Example 1 are listed. In Table 3, re denotes a radius of curvature of a reference sphere of the seventh surface of the third lens L5 composing the second lens group G2, and ro denotes a radius of curvature of a reference sphere of the eighth surface.
As shown above, in Example 1, the above-described conditional expressions (1) and (2) are satisfied.
Various values associated with Example 2 are listed in Table 4.
In the zoom eyepiece lens system EL2, upon zooming, the second lens group G2 and the third lens group G3 move along the optical axis in opposite directions with each other, and the field stop FS also moves along the optical axis independently. Accordingly, a distance d3 along the optical axis between the first lens group G1 and the second lens group G2, a distance d8 along the optical axis between the second lens group G2 and the field stop FS, a distance d9 along the optical axis between the field stop FS and the third lens group G3, and the back focal length Bf are varied upon zooming. The eye-relief ER, and variable distances with respect to each focal length of the system in the low magnification end state and the high magnification end state are shown in Table 5.
In the following Table 6, values for respective conditional expressions according to Example 2 are listed. In Table 6, re denotes a radius of curvature of a reference sphere of the seventh surface of the third lens L5 composing the second lens group G2, and ro denotes a radius of curvature of a reference sphere of the eighth surface thereof.
As shown above, in Example 2, the above-described conditional expressions (1) and (2) are satisfied.
Various values associated with Example 3 are listed in Table 7.
In the zoom eyepiece lens system EL3, upon zooming, the second lens group G2 and the third lens group G3 move along the optical axis in opposite directions with each other, and the field stop FS also moves along the optical axis independently. Accordingly, a distance d3 along the optical axis between the first lens group G1 and the second lens group G2, a distance d8 along the optical axis between the second lens group G2 and the field stop FS, a distance d9 along the optical axis between the field stop FS and the third lens group G3, and the back focal length Bf are varied upon zooming. The eye-relief ER, and variable distances with respect to each focal length of the system in the low magnification end state and the high magnification end state are shown in Table 8.
In the following Table 9, values for respective conditional expressions according to Example 3 are listed. In Table 9, re denotes a radius of curvature of a reference sphere of the seventh surface of the third lens L5 composing the second lens group G2, and ro denotes a radius of curvature of a reference sphere of the eighth surface thereof.
As shown above, in Example 3, the above-described conditional expressions (1) and (2) are satisfied.
Various values associated with Example 4 are listed in Table 10.
In the zoom eyepiece lens system EL4, upon zooming, the second lens group G2 and the third lens group G3 move along the optical axis in opposite directions with each other, and the field stop FS also moves along the optical axis independently. Accordingly, a distance d3 along the optical axis between the first lens group G1 and the second lens group G2, a distance d8 along the optical axis between the second lens group G2 and the field stop FS, a distance d9 along the optical axis between the field stop FS and the third lens group G3, and the back focal length Bf are varied upon zooming. The eye-relief ER, and variable distances with respect to each focal length of the system in the low magnification end state and the high magnification end state are shown in Table 11.
In the following Table 11 [sic], values for respective conditional expressions according to Example 4 are listed. In Table 11 [sic], re denotes a radius of curvature of a reference sphere of the seventh surface of the third lens L5 composing the second lens group G2, and ro denotes a radius of curvature of a reference sphere of the eighth surface thereof.
As shown above, in Example 4, the above-described conditional expressions (1) and (2) are satisfied.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-260919 | Oct 2007 | JP | national |
This application is a continuation of International Application No. PCT/JP2008/067976 filed Sep. 26, 2008.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5663834 | Koizumi | Sep 1997 | A |
| 6384984 | Ishii et al. | May 2002 | B1 |
| Number | Date | Country |
|---|---|---|
| 9-80326 | Mar 1997 | JP |
| 2001-242390 | Sep 2001 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20100149649 A1 | Jun 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2008/067976 | Sep 2008 | US |
| Child | 12709226 | US |
