JPS61182011A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a zoom lens consisting of the small number of constitutional lenses while keeping high performance by constituting the zoom lens of a single lens having convex surfaces on both the sides and having a positive refractive index at a specific condition, a single lens having convex surfaces on both the sides and a positive refractive index as a whole and arranged with a comparatively large air space from the 1st lens and a joint lens. CONSTITUTION:The 1st lens group G1 consists of single lens having a negative refractive index and two lenses having positive refractive indexes arranged from the object side successively, the 2nd lens group G2 consists of a single lens having a negative refractive index and a joint lens, the 3rd lens group G3 consists of a single lens having a negative refractive index, the 4th lens group G4 consists of a single lens having convex surfaces on both the sides and a positive refractive index, and the 5th lens group is arranged with a comparatively large air interval from the G4 and consists of a single lens having convex surfaces on both the sides and a positive refractive index and a joint lens consisting of a negative refractive index lens and a positive refractive index lens. To reduce the number of lenses while keeping high performance, the conditions of formulas (1)-(5) and the conditions that the 4th and 5th groups have aspherical surfaces respectively should be satisfied.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a zoom lens for a video camera, and in particular to a high-performance zoom lens that reduces the number of lenses by utilizing an aspherical surface and an appropriate relay lens system. .

BACKGROUND OF THE INVENTION In addition to improving operability and functionality, there is a strong demand for cost reduction in recent video cameras, and there is a strong demand for a zoom lens that maintains high performance while reducing the number of lenses.

Current lenses with an F number of approximately 1.4 and a zoom ratio of approximately 6x have three lenses in the focusing section.

Many lenses use 3 lenses in the variator section, 1 lens in the compensator section, and 7 to 8 lenses in the relay lens system, making the total number of lenses in the system 14 to 16 (for example, JP-A-67-19709, JP-A-67-19709
8-108511).

Problems to be Solved by the Invention It has been difficult to significantly reduce the number of lenses in such conventional spherical zoom lenses.

The present invention has been made in view of the above points, and an object of the present invention is to provide a zoom lens having as few as 11 lenses, an F number of about 1.5 or less, and a zoom ratio of about 6 times.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention focuses on reducing the number of elements in the relay lens system, and creates a zoom lens with fewer elements by utilizing aspherical surfaces and creating an appropriate relay lens type. It's something you get. The relay lens system is composed of a double-convex single lens with positive refractive power, a double-convex single lens with positive refractive power, and a cemented lens, which are arranged with a relatively large air distance from the double-convex single lens.

Function: With the above-described configuration, the present invention can realize a zoom lens with a small number of lenses while maintaining high performance by creating a new relay lens type using an aspherical surface and appropriately selecting its optical parameters.

Embodiment FIG. 1 is a block diagram showing an embodiment of the zoom lens of the present invention. In Figure 1, 01 is the first group as a focusing unit with positive refractive power, G2 is the second group as a variator unit that has negative refractive power and changes magnification by moving on the optical axis, and G3 is A third group, G4. G5 indicates a fourth group and a fifth group, respectively, which constitute a relay lens system, and G6 indicates a sixth group, which is a flat plate corresponding to a crystal filter or a face plate of an image pickup tube. 1st
The group G1 consists of one lens with negative refractive power and two lenses with positive refractive power in order from the object side, the second group G2 consists of a single lens with negative refractive power and a cemented lens, and the third group G2 consists of a single lens with negative refractive power and a cemented lens. G3 is composed of a single lens with negative refractive power. The fourth group G4 is composed of a biconvex single lens with positive refractive power, and the sixth group G5 is composed of a double convex single lens with positive refractive power.
It is arranged with a relatively large air distance from the lens and consists of a double-convex single lens with positive refractive power and a cemented lens of a lens with negative refractive power and a lens with positive refractive power.

In order to maintain high performance and reduce the number of lenses in the zoom lens of the present invention, it is necessary to satisfy the following conditions.

(1) 1.8fW<fR×2.9fW (2) 1.
2tn<14<1. efn) 1. OfRkufsku1.6fR (4) o, 9tsfs<fs<1. ef5(@
0.3 fs < r+e < O-7fs (6) 4th
The group and the fifth group each have an aspherical surface. However, f- is the focal length of the entire system at the wide-angle end, 14ef5.
fR is the focal length of the fourth group, fifth group, and relay lens system, fs is the focal length of the single lens with positive refractive power in the sixth group, and r19 is the radius of curvature of the cemented surface of the cemented lens in the fifth group. shows.

Next, we will add an explanation of the conditional expression. Condition 0) is a condition that gives power to the relay lens system, and if it deviates from the lower limit, it can be made compact, but the radius of curvature of some surfaces in the relay lens system becomes small, making it difficult to correct aberrations.

Although it is easy to correct Z and aberrations beyond the upper limit of condition (1),
This is not preferable because the lens system becomes larger.

Condition (2) is a condition regarding the power of the fourth group G4 in the relay lens system; if the lower limit is exceeded, the pack focus will not be short; if the upper limit is exceeded, the light flux exiting the fourth group G4 will be reduced. becomes a diverging light beam, so that the refractive power of the fifth group G5 and the spherical aberration of the lens, which has a large ray height, worsen.

Condition (3) is a condition that, together with the power of the fifth group G5 and condition (2), defines an appropriate distance from the fourth group G4.If the upper limit is exceeded, the exit pupil position is close to the image pickup tube. Not desirable as a lens for a video camera. If the lower limit of condition (3) is exceeded, the refractive power of the fifth group G5 will be too strong and spherical aberration will be overcorrected.

Condition (4) is a condition regarding the power of the biconvex single lens in the fifth group G6, and if the upper limit is exceeded, the lens system with a long pack focus cannot be made compact.

If the lens deviates from the lower limit of condition (4), the puck focus will be too short and the exit pupil position will be too close to the image pickup tube, making it undesirable as a lens for a video camera.

Condition (5) defines the radius of curvature of the cemented surface of the cemented lens in the fifth group G5; if the lower limit is exceeded, the curvature becomes too steep and high-order spherical aberration occurs.

If the upper limit of condition (5) is exceeded, it becomes difficult to correct chromatic aberration.

The condition (6) that the fourth group G4 and the fifth group G5 each have an aspherical surface means that the aperture aberration of a large aperture with an F number of about 1.0 to 1.5 due to the extremely small number of constituent elements. This is essential for correcting off-axis aberrations. Aberration correction is effectively performed by arranging aspheric surfaces with large air gaps. The aperture is placed immediately before or after the fourth group G4. Therefore, the fourth group G4
is the position where the light beam becomes the thickest in the relay lens system, and the aspheric surface here is effective for correcting aperture aberration.

However, that alone is not enough, and the effect is exerted in combination with the aspheric surface of the fifth group G6. The fifth group G6 corresponds to the part of the relay lens system where the off-axis chief ray becomes high, so it is effective in correcting off-axis aberrations.

Further, in order to make the lens compact, it is desirable that the focal length f2 of the second group G2 satisfies the following conditions.

(7) 1.1fvt<1f21<1-Bf” In order to construct a compact zoom lens, it is crucial to especially strengthen the power of the second group G2 that performs magnification change.The upper limit of condition (7) If it exceeds the lower limit of condition (7), it is easy to correct aberrations, but the lens system becomes large, which is undesirable.If the lower limit of condition (7) is exceeded, it can be made compact, but the curvature of some surfaces in the second group G2 is severe. This makes it difficult to correct aberrations.

To realize a compact and high-performance zoom lens for a video camera with an 11-element configuration with an F nanobar of approximately 1.0 to 1.6 and a zoom ratio of approximately 6 times under the lens configuration and conditions based on the present invention. was completed.

Examples that meet these conditions are shown below. rl, r in the table
2... is the radius of curvature of each lens surface counted in order from the object side, dI * d2... is the wall thickness or air gap between lens surfaces, nl, n2. . . . is the refractive index of each lens for the d-line, and C1. C2. ... is Atsbe's number.

In addition, surfaces with an aspherical shape (indicated by this mark) are specified by the following indication.

However, 2: Distance from the tangential plane of the aspherical vertex of a point on the aspherical surface with height y from the optical axis: y: Height from the optical axis C2 Curvature of the aspherical vertex (=1/r) k : Conic constant, E, F, G: Aspherical coefficient (below the margin) − Dimension 0
of 11 ″′
″′ ″′ Go to 2 O+ ~ Vl @ 1.
@ [phase] --
−λ ≧ ≧ λ ≧
A λ ≧111 ψ
N ψ -
ro-to 1: day to day
-Japanese -Ro■ Dimension Or Dimension 0
10 − = Pus l11N ψ
■ --A :h λ
≧ ≧ ≧ λ
A? + -F? +
-F SE -1111II 11
II 1111 11 units
I:l:I:I:I: α gr ward co o
o tv-t-1@
■ Figures 2, 3, and 4 show the aberration performance of Example 1 at the wide-angle, standard, and telephoto ends, respectively, and Figures 5, 6,
FIG. 7 is a wide-angle view of Example 2.

FIG. 8 shows aberration performance at standard and telephoto ends.

FIG. 9 and FIG. 10 show the aberration performance of Example 3 at the wide-angle, standard, and telephoto ends, respectively. In the diagram of spherical aberration, g indicates spherical aberration with respect to the g-line. Also, in the diagram of astigmatism, m is the curvature of field in the meridial direction.

j indicates field curvature in the sagittal direction. Example 1 from each figure
．． Example 2. It can be seen that both Example 3 had good optical performance.

Effects of the Invention As is clear from the above explanation, under the lens configuration and conditions of the present invention, the F number is approximately 1.0 to 1.5 and the zoom ratio is approximately 6 times with a very small number of 11 lenses. We were able to create a compact and high-performance zoom lens.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a zoom lens according to an embodiment of the present invention, Figs. 2, 3, and 4 are various aberration diagrams of embodiment 1, and Figs. Various aberration diagrams of Example 2, Fig. 8,
FIG. 9 and FIG. 10 are diagrams showing various aberration diagrams of Example 3. Note that in the diagram of spherical aberration, g indicates spherical aberration with respect to the g-line, and in the diagram of astigmatism, m indicates curvature of field in the meridional direction, and S indicates curvature of field in the sagittal direction. In Fig. 1, G1: first group as a focusing section G2: second group as a pariator section G3: third group as a compensator section G4: fourth group forming part of an IJ lens G5: part of an IJ lens 5th group G6: Flat crystal filter Name of agent Patent attorney Toshio Nakao and 1 other person 1st
Figure f ef--fu I-toshin') "fp toshi" (d1E potato QJ
---1 Ruins-q -fP Gorosu 51tgm
lInunoi (mm + M sulfur 1.1 (me
++! 1m 'inu+ (y, Jutrm
q's)'teJ1m) -+IFJ,'IK
JEonm) tlflIIZj(y, t#
kIJZ'l(rm+l;'R,q;Lrn
m) i LoliZ ”x (% j formation j n Z difference, l,, l, l.

Claims (1)

[Claims] (1) In order from the object side, a first group as a focusing section having positive refractive power, and a variator section having negative refractive power and changing magnification by moving on the optical axis. The second group is connected to the variable magnification system formed by the first, second, and third groups, and the third group as a compensator that keeps the image plane that changes due to the movement of the variator section at a constant position from the reference plane. The first group consists of one lens with negative refractive power and two lenses with positive refractive power, and the second group consists of a single lens with negative refractive power and a relay lens system with negative refractive power. It is composed of a cemented lens, the third group is composed of a single lens with negative refractive power, and the relay lens system is composed of a double convex single lens with positive refractive power. It consists of a fifth group consisting of a biconvex single lens with positive refractive power and a cemented lens of a lens with negative refractive power and a lens with positive refractive power, which are spaced apart, and satisfy the following conditions: A zoom lens characterized by <f_6<1.6f_5 (5) 0.3f_5<r_1_9<0.7f_5 (6) The fourth and fifth groups each have an aspheric surface. However, f_W is the focal length of the entire system at the wide-angle end, f_4, f_
5. f_R is the focal length of the fourth group, fifth group, and relay lens system, f_6 is the focal length of the single lens with positive refractive power in the fifth group, and r_1_9 is the curvature of the cemented surface of the cemented lens in the fifth group. Indicates radius. ]. (2) A zoom lens according to claim 1, characterized in that when the focal length of the second group is f_2, the following conditions are satisfied [(7) 1.1f_W<|f_2|<1. 8f_W〕