JPH01219710A - Zoom lens - Google Patents

Abstract

PURPOSE:To facilitate the adjusting operation for an eccentric aberration at the time of assembly by employing positive, negative, positive, and negative four-lens-group constitution, making some or all of the lenses in a 1st lens group and at least one positive lens in a 3rd lens group eccentric from other lenses and adjusting the eccentric aberration. CONSTITUTION:This zoom lens consists of the 1st positive lens group, a 2nd negative lens group 2, a stop S, a 3rd positive lens group 3, and a 4th negative lens group in order from the object side and has positive refracting power on the whole. The eccentric aberration is generated over the entire picture plane increasingly from the wide-angle end to the telephoto end, so positive lenses G8 and G9 in the 3rd lens group 3 are moved at the telephoto zoom position in parallel to the optical axis to correct the aberration on the axis. Then all the lenses G1, G2, and G3 in the 1st lens group 1 are slanted to the optical axis to correct, specially, an off-axis aberration. Thus, the off-axis aberration and on-axis aberration are corrected almost independently and the zoom lens which maintains high optical performance at all times and has variable optical characteristics is realized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a photographic lens suitable for photographic cameras, video cameras, etc., and particularly relates to a photographic lens suitable for photographic cameras, video cameras, etc. The present invention relates to a zoom lens whose decentering aberration can be easily adjusted.

[Prior art]

In recent years, with the downsizing of -eye reflex cameras, video cameras, etc., there has been a demand for downsizing of photographic lenses as well. There is a particularly high demand for this in zoom lenses, which tend to have a relatively long overall lens length.

By the way, in general, to reduce eccentricity errors during lens assembly, it is enough to manufacture the lens shape and lens barrel with high precision, but there are limits to this, and in many cases, the big problem is how to reduce eccentricity errors. It becomes.

Conventional general lens assembly work was carried out by skilled workers, making subtle adjustments to the lens arrangement of each lens to achieve optical performance close to the lens design value. I was having a hard time working. In particular, with miniaturized zoom lenses as mentioned above, the refractive power of each lens group is relatively strong (as a result, eccentricity accuracy is extremely strict, making it time-consuming and difficult to obtain the desired optical performance. It has become.

[Problem that the invention seeks to solve]

Particularly in a zoom lens, the present invention provides a zoom lens that can achieve high optical performance by decentering a predetermined lens group with respect to the optical axis, adjusting decentering aberrations that occur during assembly without much effort. Our goal is to provide lenses.

The present invention provides a zoom lens in which a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are arranged in order from the object side. This is because a part or all of the first lens group and at least one positive lens of the third lens group are decentered with respect to other lenses to adjust decentering aberrations.

〔Example〕

The present invention will be described in detail below based on the drawings. FIG. 1 is a cross-sectional view of a zoom lens according to the present invention, in which the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the aperture stop S1 have a positive refractive power in order from the object side. and a fourth lens group having negative refractive power. Note that the third lens group and the fourth lens group have positive refractive power as a whole.

FIG. 1(A) shows the zoom position at the wide-angle end, and FIG. 1(B) shows the zoom position at the telephoto end.

In other words, when changing the magnification from the wide-angle side to the telephoto side, the fourth lens group 4 is fixed, the first lens group 1 and the third lens group 3 are moved to the object side, and the second lens group 2 is moved to the object side or the image side. I'm letting you do it.

The zoom lens shown in this embodiment includes a lens G in which the third lens group 3 has a concave surface facing toward the image surface, and a lens G with a positive refractive power having one aspherical surface (both have a small aspherical surface on the image surface side of the lens G). Further, the fourth lens group includes a lens GI5 having a negative refractive power and a lens Gas having a positive refractive power made of glass having a refractive index lower than the refractive index of the glass of the lens G+s. It is composed of lenses bonded together.

However, C++, G12 in the third lens group, G7. Eccentricity errors such as tilt and parallel movement during assembly occur in the order of Gs, Cz, and Gs, which causes many eccentric aberrations on the entire screen, both off-axis and on-axis.

This tendency becomes especially strong from the wide-angle end to the telephoto end, and as a result, the optical performance deteriorates significantly.

Therefore, in this embodiment, at the telephoto zoom position, Gs with positive refractive power is arranged in the third lens group on the image plane side from the aperture S.

The lens group consisting of G9 is moved parallel to the optical axis, that is, decentered, and eccentric aberrations, particularly axial aberrations, caused by manufacturing and assembly are corrected in a well-balanced manner.

With this correction, off-axis aberrations do not change significantly (,
Center aberration correction is possible.

Next, preferably the entire first lens group Gl, G2. G
The three lens groups are tilted with respect to the optical axis, that is, decentered, and eccentric aberrations, particularly off-axis aberrations, caused by manufacturing and assembly are corrected in a well-balanced manner. With this correction, there is almost no on-axis fluctuating aberration (off-axis correction is possible).

That is, it becomes possible to correct off-axis aberrations and on-axis aberrations almost independently.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis,
The traveling direction of light is positive, R is the paraxial radius of curvature, A, B,
When C, D, and E are each aspherical coefficients, numerical example F=36.0 to 132. FNO=1: 3.6~
4.62ω=61.7°~18.6°R1=318
．． 08 D l = 2.15 N 1 = 1.8051
8 ν1=25.4R2= 67.95 D 2
=7.00 N2=1.65160 C2=58
．． 6R3= -163,95D 3=0.12R4=
44.95 D 4=4.20 N 3=1.6
9680 ν3=55.5R5= 119.18
D 5 = Variable R6 = 100.66 D 6
=1.37 N4=1.88300 C4=40
,8R7= 19.76 D 7=5.83R8=
-37,65D 8=1.18 N 5=1.8
8300 ν5=40.8R9=83.24
D9=1.73R10=47.94
D10=4.70 N6=1.84666
White = 23.9R11 = -38,01D
11=0.88R12=-26,70D12=1
,03 N 7=1.81600 Schiff=46
．． 6R13=-83,05D13=variable R14=
53.26 D14=3.40 N 8
=1.61800 shi8=63.4R15=-
629,24D15=0.15R16=38.
32 D16=3.40 N9=1,60
311 ν9 = 60.7R17 = 16
84.80 D17=0.15R18=3
5.63 D18=2.70 Nl0=1.
51633 Si1o=64. lR19=5
5.61 D19=0.15R20=2
2.31 D20=5.54 N11=1.4
8749 ν11 =70. lR21=-162,
15D21=7.68 N12=1.85026
ν12=23.9R22=14.89
D22=4.86R23=33.69
D23=3.5 N15=1.57309
C13=42,6R24=-35,33D24=
1.0 N14=1.84666 ν14=
23.9R25=-63,72D25=variable R26
= -37,90D26=0.98 N15
=1.83481 Shi15=42.7R27=
-279,06D27=4.90 N16=
1.53172 Shi16=48.9R28=
-27,90 R25: Aspherical surface Aspherical coefficient A= O B= 2.957xlO-' C= -8,998xl O-" D= -7,522X10-" E= 0 Next, numerical implementation is shown in Figure 2 The MTF values in the example are shown.

In the MTF value, Y is the image height, (A) is when it is ideally assembled and there is no eccentricity, and (B) is when the assembly is performed from the first lens group to the fourth lens group as shown in Table 1. When there is eccentricity, (C) shows G8. of the third lens group. When the G9 lens is parallel decentered (0.08 mm), (D)
further tilts the entire first lens group with respect to the optical axis (-0, 2
′) to adjust the optical characteristics.

As shown in FIG. 2, it can be seen that according to this example, by decentering a predetermined lens group, decentering aberrations can be favorably corrected and high optical performance can be maintained.

Although the lens barrel that holds the photographic lens is not particularly shown, the lens to be decentered is fixed to a small lens barrel, and this small lens barrel is installed in a hole in the wall perpendicular to the optical axis of the outer lens barrel. The small lens barrel is then moved and the screws are tightened firmly when the desired performance is achieved.The other constituent lenses have the same structure as before and are attached to the outer lens barrel. However, in conventional assembly work, the subsequent lens was carefully positioned relative to the previously fixed lens, but in this example, it is possible to simply fix the lens without taking such consideration. That's why.

〔Effect of the invention〕

According to the present invention, in a zoom lens having the above-described lens configuration, decentering aberration of a predetermined lens group with respect to the optical axis is adjusted to achieve a zoom lens with variable optical characteristics that can always maintain high optical performance. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a lens according to a numerical example of the present invention, and FIG. 2 is an MTF value of a numerical example of the present invention. A is when there is no eccentricity, B is when each eccentricity shown in Table 1 is made at A, and C is G8 at B. When G9 is corrected, D is Gl at C,
G2. The MTF when G3 is corrected is shown. In the figure, Gi is the i-th lens group or i-th lens, S is the aperture, and in the aberration diagram (A) is an object at infinity, ΔM is the meridional image surface, and ΔS is the sagittal image surface.

Claims (1)

[Claims] In a zoom lens in which a first lens group with a positive refractive power, a second lens group with a negative refractive power, and a third lens group with a positive refractive power are arranged in order from the object side, one of the first lens groups A zoom lens characterized in that at least one positive lens of the third lens group is decentered with respect to other lenses to adjust eccentric aberration.