JPH0720367A - Variable lens system - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a compact and high-performance variable power lens system. [Structure] A variable-magnification lens system capable of switching between two and three times the two focal points is composed of a wide-angle conversion lens system 1 and an imaging lens system 3. By forming through holes 1c and 1d in the center of the lens barrel of the wide-angle conversion lens system 1 and rotating the lens barrel of the wide-angle conversion lens system 1 by 90 degrees,
The angle of view of only the imaging lens system 3 (telephoto side) and the angle of view through the wide-angle conversion lens system 1 (wide-angle side) can be switched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable power lens system used for, for example, a video camera, and a variable power lens system capable of variable power of about 2 to 3 times.

[0002]

2. Description of the Related Art A lens system capable of changing the magnification by about 2 to 3 times that of a conventional one is a wide-angle system imaging lens 10 as shown in FIG.
In combination with the telephoto converter 11 having a concave lens system, the imaging lens alone is moved to the wide-angle side, the imaging lens 10 is moved to the object side on the optical axis, and the telescopic converter 11 is inserted behind the imaging lens 10. There is a variable magnification lens system that converts to the telephoto side.

Further, as shown in FIGS. 6 and 7, there is a so-called two-group zoom lens system which changes the relative distance between the concave lens groups 20 and 30 and the convex lens groups 21 and 31 to change the focal length of the entire system. Yes There are a concave lens group preceding type (Fig. 6) and a convex lens group preceding type (Fig. 7).

[0004]

By the way, in the above-described conventional variable power lens system, it is necessary to move the lens group in the optical axis direction when performing variable power. In FIG. 5, a telephoto converter is further inserted or retracted. It requires complex movements to make it happen. Further, in the two-group zoom lens system shown in FIGS. 6 and 7,
The two lens groups must be moved in different directions or with different amounts of movement. Therefore, a complicated zooming mechanism such as a cam is required, and it is inevitable to increase the size, and it is difficult to reduce the manufacturing cost.

Further, in the conventional variable power lens system described above,
The change in F-number between the wide-angle side and the telephoto side is almost determined by the zoom ratio and the refractive power arrangement of each lens group. If the F-number is set brighter on the wide-angle side with a deep depth of field, the F-number on the telephoto side will also increase. The value is not too dark and the depth of field is shallow. There is no problem if the autofocus mechanism is adopted, but it is very inconvenient when the fixed focus method is adopted for the purpose of reducing the manufacturing cost.

Furthermore, when the fixed focus method is adopted, when the focus adjustment is performed for the hyperfocal length during manufacturing and assembly, the stop position of the lens group that moves with zooming is adjusted,
A mechanism for finely adjusting the relative position between the lens barrel and the image sensor while maintaining parallelism is required, which complicates the mechanism and makes it difficult to maintain the performance.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of the prior art and to provide a variable-magnification lens system that is small in size, inexpensive, and has well-corrected aberrations.

[0008]

The structure of the present invention as set forth in claim 1 will be described with reference to FIG. 1. A wide-angle conversion lens system 1, a diaphragm 2, and an imaging lens system which are substantially afocal in order from the object side. In the variable magnification lens system mainly composed of the image forming lens system 3 having the filter 4 and the image pickup device 5 (for example, CCD) behind the image forming lens system 3, the wide-angle conversion lens system 1 is a concave lens group. 1a and a convex lens group 1b are arranged with an air gap, and two through holes that are orthogonal to the optical axis of the wide-angle conversion lens system 1 are formed in the lens barrel of the wide-angle conversion lens system 1 at the portion forming the air gap. By providing 1c and 1d, the lens barrel of the wide-angle conversion lens system 1 can be approximately 90
By rotating the lens through the through holes 1c and 1d, it is possible to take a picture with the angle of view of only the imaging lens system 3 (hereinafter referred to as the telephoto side), and the angle of view through the wide-angle conversion lens system 1 (hereinafter It is characterized in that it is switchable so that it can be shot on the wide-angle side.

Of the above through holes, the hole 1d closer to the diaphragm is used as a fixed diaphragm having a smaller aperture opening diameter to limit the open F value when photographing on the telephoto side than when photographing on the wide angle side. The imaging lens system 3 can be moved in the optical axis direction, and the relative position with respect to the image sensor can be adjusted. In Figure 2,
The state where the lens barrel of the wide-angle conversion lens system 1 is rotated by 90 degrees to the telephoto side is shown.

A specific lens structure of the invention described in claim 7 will be described with reference to FIG.

The wide-angle conversion lens system 1 constitutes, in order from the object side, the concave lens group 1a by a cemented lens of a concave first lens L ₁ and a convex second lens L ₂ and a concave third lens L _3. and constitute the convex lens group 1b by the fourth lens L ₄ of the convex lens, with at least one surface of the first lens L ₁ of the concave lens is aspherical, plastic aspherical lens of the first lens L ₁ of the concave lens On the other hand, the imaging lens system 3 is, in order from the object side, a fifth lens L ₅ that is a convex lens, a cemented lens of a sixth lens L ₆ of a convex lens and a seventh lens L ₇ of a concave lens, and an eighth lens L of a convex lens. _It is composed of ₈ and is characterized by satisfying the following respective conditions.

(1) 1.8 <| f ₁ / f _W | <3.6 (2) 0 <Δχ ₁ (3) ν ₂ <40 (4) 60 <ν ₄ (5) 1 <f ₅ / f _T <2 (6) 0.5 <d ₅ / f _T <1 (7) 1.75 <(n ₅ + n ₈ ) / 2 (8) 0.05 <n ₇ −n ₆ <0.3 ( 9) 0.7 <SL / f _T <1.4 where f _i : focal length of the i-th lens L _i f _W : focal length of the entire system on the wide angle side f _T : focal length of the entire system on the telephoto side Δχ ₁ : Deviation of the aspherical surface of the r ₁ surface from the paraxial spherical surface in the effective diameter ν _i : Abbe number of the i-th lens L _i d _i : i-th surface spacing n _i : refraction of the _i- th lens L _i at d line Rate SL: Distance from diaphragm to final surface

[0013]

According to the first aspect of the present invention, since it is not necessary to move the lens group in the optical axis direction for zooming, a complicated interlocking mechanism such as a cam is not necessary, and a wide-angle conversion lens system lens barrel is provided. It can be configured with a simple mechanism that only rotates about 90 degrees. If the mechanism is simple, it will be extremely advantageous for downsizing and weight reduction and cost reduction.

When the zoom ratio is set large, the depth of field on the telephoto side becomes shallower in inverse proportion to the square of the zoom ratio than on the wide angle side if the F value is the same, so that a fixed focus is realized. In order to achieve this, the F-number on the telephoto side must be darkened, but the F-number on the telephoto side can be freely set to be dark by limiting the open F-number with the fixed aperture formed by the through hole.

The above-mentioned imaging lens system has its aberrations corrected well by itself, and is fixed during zooming. Therefore, this lens is moved back and forth with respect to the image sensor to adjust the hyperfocal length. Even if you do, there is no performance deterioration, and it will not be affected by durability etc. during use.

According to the invention described in claim 7, when the wide-angle conversion lens system is placed in front of the imaging lens system, the Petzval sum (hereinafter referred to as ΣP) becomes small, and the concave lens group and the convex lens of the wide-angle conversion lens system are reduced. If the space between the lens unit and the lens unit is narrowed, ΣP becomes even more negative, making it difficult to correct astigmatism. In order to achieve both the miniaturization and the appropriate value of ΣP, it is effective to concentrate the negative refracting power on the object side and the positive refracting power on the image side of the wide-angle conversion lens system. ₁ is a concave lens, 4th lens L ₄
Is a convex lens. The first lens L ₁ that has a concave lens, because there is no lens to correct the negative distortion generated by the first lens L ₁ effectively, the at least one surface of the first lens L ₁ is aspherical This suppresses the occurrence of negative distortion.

Although the glass aspherical lens has a high manufacturing cost, the plastic aspherical lens has a lower manufacturing cost than the glass aspherical lens, which is advantageous for a lens whose cost is to be reduced. However, the plastic lens has a large temperature change in the coefficient of linear expansion and the refractive index as compared with glass, and thus has a drawback that the temperature change in the focal length is large. The use of plastic for the lens element, which has a great influence on the focus movement of the entire system due to the temperature change of the focal length, causes a fatal problem for the fixed focus lens. In the present invention,
By using plastic for the first lens L _1, which has the thinnest luminous flux, we succeeded in minimizing the effect of temperature change of the focal length on the focus movement of the entire system while achieving both performance improvement and cost reduction. did.

Next, the above conditional expressions will be described in detail.

The conditional expression (1) is a condition mainly for achieving both miniaturization and setting .SIGMA.P to an appropriate value. When the lower limit is exceeded, .SIGMA.P becomes too negative and the field curvature is difficult to correct. Become. If the upper limit is exceeded, in order to maintain the zoom ratio, the distance between the first lens L ₁ and the fourth lens L ₄ becomes large, and the object of downsizing cannot be achieved.

The conditional expression (2) defines the shape of the aspherical surface. By making Δχ ₁ positive, negative distortion and overcorrected astigmatism can be corrected.

The conditional expression (3) is defined by the first lens L ₁ and the third lens
The present invention relates to correction of lateral chromatic aberration generated from the lens L ₃ , and can be excellently corrected by reducing the Abbe number of the second lens L ₂ having a high chief ray height to 40 or less.

The conditional expression (4) relates to the correction of the axial chromatic aberration of the wide-angle conversion lens system. Since the second lens L ₂ of the convex lens is made of glass having a small Abbe's number according to the condition (3), The above chromatic aberration tends to be undercorrected. If the fourth lens L ₄ is an achromatic cemented lens, the correction is easy, but the cost is high. Therefore, in order to balance the cost and the chromatic aberration, it is appropriate to select glass under the condition (4).

The conditional expression (5) is a condition for appropriately shortening the back focus. If the lower limit is exceeded, the back focus becomes too short, and a low-pass filter or an infrared ray inserted between the lens and the image sensor is used. The cut filter does not fit. Beyond the upper limit, the back focus becomes longer than necessary and miniaturization cannot be achieved.

The conditional expression (6) is a condition for achieving both downsizing and downsizing by forming a through hole in the lens barrel of the wide-angle conversion lens system and taking a picture only with the imaging lens system.
If the value goes below the lower limit, ghost may occur due to the reflected light from the r ₅ surface or r ₆ surface, or vignetting may occur on the screen due to the through hole on the object side. If the upper limit is exceeded, the miniaturization, which is the object of the present invention, cannot be achieved.

The conditional expression (7) is a condition for correcting the spherical aberration to be small and brightening the F value, and is the refractive index of the glass of the fifth lens L ₅ and the eighth lens L ₈ having positive refractive power. By increasing the, the curvature of the above two lenses can be weakened,
It is possible to suppress the occurrence of spherical aberration that is insufficiently corrected and to make the F value bright.

The conditional expression (8) is a condition for satisfactorily correcting the spherical aberration that is suppressed from being generated under the above condition (7).
When the value goes below the lower limit, the curvature of r ₁₁ becomes too strong to correct spherical aberration, and the curvature of the spherical aberration curve becomes large.
If the upper limit is exceeded, the share of the positive refractive power of the r ₁₀ surface becomes small, and the spherical aberration generation amount of the entire imaging lens system becomes large.
Correction becomes difficult.

The conditional expression (9) is a condition for appropriately increasing the exit pupil distance (distance from the exit pupil to the image plane). If the lower limit is exceeded, the exit pupil distance becomes too short. Depending on the characteristics of the image sensor, if the exit pupil distance becomes too short, there may be a phenomenon that the amount of light is insufficient at the peripheral portion of the screen, and the exit pupil distance must be at least three times the screen diagonal. On the other hand, when the value exceeds the upper limit, it becomes difficult to correct astigmatism and it becomes difficult to lengthen the back focus.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, L ₁ to L ₈ are respectively the first
The lens is the eighth lens, and L ₁ to L ₄ constitute the wide-angle conversion lens system 1, of which L ₁ to L ₃ constitute the concave lens group 1a, L ₄ constitutes the convex lens group 1b, and L ₅ to L ₈ The imaging lens system 3 is constituted by. Reference numeral 4 is a plane-parallel glass corresponding to a filter, 5 is an image sensor, and 2 is a diaphragm.

The wide-angle conversion lens system 1 is held by a lens barrel 6, and the lens barrel 6 has through holes 1a and 1b.
The optical axis of the lens barrel 6 passes through the intersection of the optical axis connecting the centers of the through-holes 1a and 1b and the optical axis of the wide-angle conversion lens system 1 and is orthogonal to both optical axes. It is held so that it can rotate 90 degrees.

Next, numerical examples of this embodiment will be shown below.

R ₁ 98.52 d ₁ 1.5 n ₁ 1.492 ν ₁ 57.2 r ₂ 4.61 d ₂ 2.19 r ₃ ∞ d ₃ 3.75 n ₂ 1.62004 ν ₂ 36. 3 r ₄ −4.5 d ₄ 1. n ₃ 1.77250 ν ₃ 49.6 r ₅ ∞ d ₅ 8.69 r ₆ ∞ d ₆ 1.7 n ₄ 1.48749 ν ₄ 70.4 r ₇ −9.81 d ₇ 3. _{r 8 27.7 d 8 1.3 n 5} 1.80610 ν 5 40.7 r 9 -27.7 d 9 0.2 r 10 6.15 d 10 3.44 n 6 1.70154 ν 6 41. _{2 r 11 -6.15 d 11 0.8 n} 7 1.84666 ν 7 23.8 r 12 4.1 d 12 1.55 r 13 -31. d ₁₃ 2.48 n ₈ 1.83400 ν ₈ 37.3 r ₁₄ −6.818 Aspherical coefficient A ₄ A ₆ r ₁ surface 1.08 × 10 ⁻³ −7.11 × 10 ⁻⁶ r ₂ surface 6 0.25 × 10 ⁻⁴ 7.25 × 10 ⁻⁵ However, the depth χ _i of the i-plane is defined as follows, where H is the height from the optical axis.

Χ _i = H ² / r _i {1+ (1-H ² / r _i ² )
^1/2 } + A ₄ · H ⁴ + A ₆ · H ⁶ H = 5.0, Δχ ₁ = 0.5639 Parallel plane glass corresponding to the filter 4: thickness 4.3,
n _d = 1.51633 The aperture is the front side of the r ₈ surface 1.5 The aperture open diameter: φ5.9 The diameter of the through hole 1d: φ2.9, the position of the through hole 1d is the front side of the aperture 1.5 The wide-angle side f _W = 4.08, F2.1, reference distance: r ₁ -580 to the telephoto side f _T = 1.29, F4.2, reference distance: r ₈
Back focus at -2600 reference distance from the surface: 5.86 (air-equivalent value) exit pupil: -19.24 (from the image _{plane) f 1 / f w = -2.4220} f 5 / f T = 1.4128 d _{5 / f T = 0.7071 (n} 5 + n 8) of _{/2=1.82005 n 7 -n 6 = 0.14512 S} L / f T = 0.9170 this numerical example, each of the wide-angle side and the telephoto side Aberration curve diagram,
Shown in FIGS. 3 and 4.

[0034]

As described above, according to the present invention,
Since it is not necessary to move the lens in the optical axis direction at the time of zooming, the zooming mechanism can be simplified and downsized as compared with the conventional one.

Further, since the variable power mechanism is simplified as compared with the conventional one, the manufacturing cost can be reduced.

Further, since the open F value on the telephoto side can be arbitrarily set by the fixed aperture, the depth of field can be deepened and a fixed focus lens can be obtained.

Further, by separating the mechanism for adjusting the focus on the hyperfocal distance from the variable power mechanism, it is possible to facilitate the focus adjustment at the time of manufacturing and assembling.

Further, by separating the mechanism for adjusting the focus on the hyperfocal distance and the zooming mechanism, it is possible to eliminate the possibility that the durability of the zooming mechanism will lead to aged deterioration of the image plane position.

Further, by using an aspherical plastic lens as the first lens, it is possible to achieve high performance and a reduction in manufacturing cost while suppressing the influence of the temperature change of the image plane position.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a state in which a variable power lens system of an embodiment of the present invention is set on a wide angle side.

FIG. 2 is a configuration diagram showing a state in which the variable power lens system is set on a distant side.

FIGS. 3A to 3C are aberration curve diagrams showing spherical aberration, astigmatism, and distortion on the wide-angle side of the variable power lens system, respectively.

FIGS. 4A to 4C are aberration curve diagrams showing spherical aberration, astigmatism, and distortion on the telephoto side of the variable power lens system, respectively.

FIG. 5 is a schematic diagram showing a conventional scaling method.

FIG. 6 is a schematic diagram showing another conventional scaling method.

FIG. 7 is a schematic diagram showing another conventional scaling method.

[Explanation of symbols]

 1 ... Wide-angle conversion lens system 2 ... Aperture 3 ... Imaging lens system 1a ... Concave lens group 1b ... Convex lens group 1c, 1d ... Through hole

Claims (7)

[Claims] 1. In a variable power lens system mainly used for a video camera, which comprises, in order from the object side, a wide-angle conversion lens system that is almost afocal and a diaphragm and an imaging lens system, the wide-angle conversion lens system is a concave lens group. The convex lens group and the convex lens group are arranged with an air gap, and a through hole perpendicular to the optical axis of the wide-angle conversion lens system is provided in a portion of the lens barrel of the wide-angle conversion lens system that forms the air gap. By rotating the lens barrel of the lens system by about 90 degrees, it is possible to shoot with the angle of view of only the imaging lens system through the through hole, or with the wide angle conversion lens system. A variable power lens system characterized in that it is switchable in this way. 2. A fixed aperture having a smaller aperture opening diameter than the aperture of the through-hole is used to make the open F-number darker when shooting at the telephoto side than when shooting at the wide-angle side. The variable power lens system according to claim 1, wherein the depth of field is increased. 3. The variable power lens system according to claim 1, wherein the imaging lens system is movable in the optical axis direction and the relative position to the image pickup device is adjustable. 4. The wide-angle conversion lens system comprises, in order from the object side, a concave first lens and a convex second lens.
The concave lens group is configured by a lens and a cemented lens of a third lens which is a concave lens, the convex lens group is configured by a fourth lens which is a convex lens, and at least one surface of the first lens of the concave lens is aspherical. The variable power lens system according to claim 1. 5. The variable power lens system according to claim 4, wherein the first lens of the concave lens is a plastic aspherical lens. 6. The image forming lens system comprises, in order from the object side, a fifth lens of a convex lens, a cemented lens of a sixth lens of a convex lens and a seventh lens of a concave lens, and an eighth lens of a convex lens. The variable power lens system according to claim 1, which is characterized in that: 7. In a variable power lens system mainly used for a video camera, which comprises, in order from the object side, a wide-angle conversion lens system which is almost afocal and a diaphragm and an imaging lens system, the wide-angle conversion lens system is arranged from the object side. In order, the first lens of the concave lens, the second lens of the convex lens and the cemented lens of the third lens of the concave lens constitute the concave lens group, the fourth lens of the convex lens constitutes the convex lens group, and the first lens of the concave lens At least one of the lenses
The surface is an aspherical surface, and the first lens of the concave lens is a plastic aspherical lens, while the imaging lens system is, in order from the object side, the fifth lens of the convex lens, the sixth lens of the convex lens, and the sixth lens of the concave lens. A variable power lens system comprising a cemented lens with 7 lenses and an eighth lens which is a convex lens, and which satisfies the following conditions. (1) 1.8 <| f ₁ / f _W | <3.6 (2) 0 <Δχ ₁ (3) ν ₂ <40 (4) 60 <ν ₄ (5) 1 <f ₅ / f _T < 2 (6) 0.5 <d ₅ / f _T <1 (7) 1.75 <(n ₅ + n ₈ ) / 2 (8) 0.05 <n ₇ −n ₆ <0.3 (9) 0 .7 <SL / f _T <1.4 where f _i : focal length of the i-th lens L _i f _W : focal length of wide-angle side total system f _T : focal length of wide-angle side total system Δχ ₁ : effective deviation from the paraxial spherical surface of the aspherical r ₁ side in the radial [nu _i: the Abbe number d _i of the i-th lens L _i: i-th surface interval n _i: refractive index at the d-line of the i-th lens L _i SL: Distance from diaphragm to final surface