JPS63285511A - Telephoto zoom lens - Google Patents

Abstract

PURPOSE:To improve operability and enable variation in frequency and to reduce the weight of the whole optical system by reducing the weight of a 1st lens group. CONSTITUTION:The 1st lens group G1 has positive refracting power and a function for focusing, a 2nd lens group G2 is a variator which has refracting power and varies in the magnification, and a 3rd lens group G3 is a compensator which has positive refracting power on the whole and hold an image plane moved by the magnification variation of the variator constant. Further, a 4th lens group G4 is a relay system which has positive refracting power and an image forming function. Then the lens group G1 has a biconvex positive lens L11 and a biconcave negative lens L13 cemented thereto in order from the object side. In the lens group G4, optical glass is used for the 1st lens L11 and plastic is used for the 2nd lens L12 and 3rd lens L13. Thus, the lens group G1 is reduced in weight to improve the operability and enable variation in frequency, and the whole optical system is reduced in weight at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an improvement in a telephoto zoom lens having a configuration of four groups, positive, negative, positive, and positive in order from the object side.

(Prior art) A first group that has a positive refractive power and performs focusing, a second group of variators that has a function of changing magnification and has a negative refractive power, and a variator group that has a function of changing magnification and has a negative refractive power. positive, negative, positive, and positive, consisting of a third group of compensators with a refractive power of
Zoom lenses with a group configuration are known.

Recently, in order to reduce the cost and weight of this type of zoom lens, it has been proposed to use a plastic lens in the lens system. However, since the refractive index of plastic changes more with temperature than that of glass, it had the fatal drawback that the focal plane of the lens would shift due to changes in temperature.

For this reason, when a plastic lens is used in a zoom lens, not only does the focal plane shift depending on the temperature, but also the focal plane at the wide end and telephoto end changes significantly when zooming. The proposal is based on Japanese Patent Application Laid-open No. 57-176015 and Japanese Patent Application Laid-open No. 58-1989 by the same applicant as this case.
65407 etc.

(Problems to be Solved by the Invention) Recently, with the introduction of AF in cameras, there has been a demand for quick focusing of the focusing lens group. However, in this type of zoom lens, the refractive power of the focusing lens group GI is relatively weak, so when focusing,
The amount of extension is quite large, and in terms of weight, the ratio of the lens group G1 to the entire optical system is quite large.
This has been a major obstacle in efforts to reduce weight. When focusing, the lens group G is extended toward the object side, which is the so-called front lens extension method, so the second lens L, which accounts for a large proportion of the entire optical system in terms of weight, is used for AF. It is difficult to move it due to

And the third lens group G for focusing.

The weight and amount of extension are quite large, so when trying to achieve AF, the load placed on the motor to move the first focusing group, that is, (the amount of movement of the focusing group) x (the weight of the focusing group) The amount of work determined by this method becomes too large and the operating time becomes extremely long, which requires a large amount of power and is therefore impractical.

To solve this problem, it is necessary to strengthen the refractive power of the lens group G to shorten the amount of movement during focusing, or to reduce the weight of the lens group Gi for focusing.

However, if you try to shorten the amount of extension during focusing by strengthening the refractive power of the lens group Gl, it will not only become difficult to correct aberrations, especially spherical aberration and astigmatism on the telephoto side, but also Fluctuations in aberrations become large. In addition, this type of zoom lens is generally heavy, making it difficult to carry.
It is inferior in terms of maneuverability. And the first lens group G
Even if you try to make the focusing group lighter by increasing the refractive power of the lens,
Since the weight of the first lens group G1, which occupies a large proportion of the entire lens system, does not change at all, it cannot contribute at all to reducing the weight of the entire optical system.

Therefore, the present invention provides the lens group G of a telephoto zoom lens.
The object of the present invention is to provide a high-precision, compact zoom lens that can improve operability and enable AF by reducing the weight of the entire optical system.

(Means for Solving the Problems) The present invention includes, in order from the object side, a first lens group G1 that has a positive refractive power and performs focusing, and a first lens group G1 that performs focusing by moving along the optical axis, and a negative lens group that performs magnification by moving along the optical axis. a second lens group G2 that is a variator with refractive power; a third lens group G that is a compensator that maintains a constant position of the image plane that changes due to the movement of the variator and has positive refractive power; The fourth lens group G is a 1/- system having an imaging function.
The main feature of the present invention is to solve the above-mentioned problems by providing a plastic lens in the lens group G.

Due to the basic configuration of the zoom lens of the present invention, (1) to
It is desirable to satisfy condition (4).

(1) 1.0 < r, /r, <2.5 (2)
0.35< l ft /rw l <0.55 (3
) 0.8 < rl /fw < 1.5 (4) 1.
0 < r, / fw < 1.6 Also, the refractive index of the i-th 1/lens component of the first group is expressed as temperature, tl %
“When t, n+1(i), nl1(j+), n
(tt), the temperature dispersion W,l of the material forming the i-th lens component of the first group is n(t,)-n(t,), where t,<1< 12, and will be more effective if the following conditions are met.

J fl, lHfr (8) O71<f/fIz-1s<0.5, where fli: Focal length at temperature t of the i-th lens component of the first group in order from the object side.

h1 The height of incidence of a paraxial ray entering the first lens component of the first group at a height h from the object side.

rI: Focal length of the first lens group G1.

rt: Focal length of the second lens group Gt.

f: I: Focal length of the third lens group G.

f4: Focal length of the fourth lens group G.

ro: Focal length of the entire system at the wide end.

r? : Focal length of the entire system at the telephoto end #! .

β11: Combined magnification of the second to fourth lens groups at the wide end.

β? : Combined magnification of the second to fourth lens groups at the telephoto end.

Si1! : Atsube number of the second lens I-+z in the lens group G1.

C1. : Atsube number of the third lens L+1 in the lens group GI.

r +z-+x: Second lens L in the lens group G
,.

and the third lens Llff.

(Function) The main feature of the present invention is that a plastic lens is used in the lens group G that performs focusing, thereby reducing the weight. Here, since the surface hardness of plastic is considerably inferior to that of glass, if a plastic lens is used for the second lens Ll+, which is closest to the object side, it is disadvantageous because it is likely to be scratched. Therefore, in the present invention, a glass lens is used for the second lens I closest to the object side of the first lens group G1, and a plastic lens for weight reduction is used as the second positive lens I- +t and second lens L
The configuration is used for the negative third lens L11 cemented to +z.

The plastic lens used in the present invention constitutes a cemented lens in the first lens group G1. The positive second lens L+z on the object side is made of low dispersion plastic, and the negative third lens L+3 on the image plane side is made of high dispersion plastic. The synthetic refractive power of the plastic cemented lens is appropriately provided, and the positive L opening of the L lens closest to the object in the L lens group GI is made of low dispersion glass to suppress the occurrence of chromatic aberration.

In the present invention, by providing a cemented lens consisting of a low-dispersion plastic lens and a high-dispersion plastic lens in the first lens group G1, the movement ΔP of the focal plane due to temperature in the first lens group G is suppressed to a small value, and the lens We succeeded in suppressing the movement of the focal plane due to the temperature of the entire system, and the change in the focal plane during zooming, to within a practical range. As mentioned above, the second lens L+z and the third lens in the first lens group G1
Since the movement of the focal plane due to temperature can be compensated for only by the cemented lens made by bonding with the lens L13, the exit angle of the light ray that passes through the lens group G, that is, the exit angle of the light ray that passes through the cemented lens made of plastic. It becomes possible to suppress changes in angle due to temperature to a small level. Therefore, it is advantageous to suppress fluctuations in aberration due to temperature. Each of the above conditions will be explained below.

Equation (1) defines the refractive power of the lens group G. If this upper limit is exceeded, it becomes impossible to downsize the variable power system made up of the first to third lens groups, and if the lower limit is exceeded, the refractive power of the first lens group G1 becomes too strong, especially Correction of aberrations on the telephoto side It becomes difficult to correct variations in aberrations at close range.

Equation (2) defines the refractive power of the second lens group G. If this upper limit is exceeded, the refractive power of the second lens group Gt as a diverging group becomes weaker, making it difficult to reduce the overall length of the zoom lens system. If the lower limit is exceeded, the Petzval sum becomes excessively negative, making it difficult to correct astigmatism and field curvature.

Equation (3) defines the refractive power of the third lens group G. If this upper limit is exceeded, the variable magnification system from the lens group G to the third lens group G will become larger, which is undesirable.
Moreover, if the lower limit is exceeded, fluctuations in various aberrations due to zooming become excessive, making correction difficult.

Equation (4) defines the refractive power of the fourth lens group G4. The fourth lens group G as an imaging group must exceed this upper limit.
4 becomes weaker, leading to an increase in the size of the imaging group, which is not preferable in terms of downsizing the lens system.

If the lower limit is exceeded, the spherical aberration, especially the spherical aberration on the telephoto side, becomes excessive and difficult to correct.

Equations (5) and (6) express the movement of the focal plane of the lens system as a whole due to temperature, and the focal plane of the lens group G due to temperature in order to keep the focal plane change during zooming within a practically sufficient range. This defines the movement range ΔP. If this range is exceeded, the movement of the focal plane due to the temperature of the entire lens system and the change in the focal plane during zooming will be excessive, which is not practical.

Equations (7) and (8) indicate the appropriate conditions for achromatization in the Luns group G by defining the apparent Abbe number and refractive power of the cemented lens made of plastic in the Luns group G. ing.

If the upper limit is exceeded, for example, when considering the short wavelength side, the axial chromatic aberration becomes excessively negative and the off-axis chromatic aberration becomes excessively positive. If the lower limit is exceeded, the axial envelopment/difference becomes excessively positive and the off-axis chromatic aberration becomes excessively negative. 6 (Example) An example will be described below. Each of the first to fourth embodiments of the present invention has a positive, negative, positive, and positive four-group configuration, and the second lens group Gl has a positive refractive power and has a focusing function. The lens group G2 is a variator that has refractive power and performs magnification change, the third lens group G3 as a whole has positive refractive power and is a compensator that keeps the image plane that moves due to the magnification change of the variator constant, and the fourth lens group Group G4 is a relay system having positive refractive power and imaging ability.

The lens group G1 includes, in order from the object side, a biconvex positive lens L11, a biconvex positive lens LIE, and a biconcave negative lens 1.1. The second lens group G2 includes positive meniscus lenses L and I with a convex surface facing the image side, and a biconcave negative lens L cemented to the positive meniscus lenses L and I.

and a biconcave negative lens Lz3, and the third lens group G1 includes a positive lens 1. with a surface having a stronger curvature facing toward the image side.
1 and the negative meniscus lens L3 bonded to it! The fourth lens group G4 includes a positive meniscus lens L41 having a surface with a stronger curvature facing the object side, and a biconcave negative lens L41.
aw, and a negative meniscus lens L4 with a surface with a stronger curvature facing the object side with a large air gap in between. and a biconvex positive lens L a a having a stronger curvature toward the object side. However, the aperture is the fourth lens group G4.
It is located closer to the object.

Further, in the present invention, in the lens group GI, optical glass is used for the second lens LIz, and plastic is used for the second lens LIz and the third lens Lea.

Regarding the movement of the focal plane due to temperature, the reference temperature is +20℃.
Corrections are made for +10°C and +50°C.

The specifications of each example at the reference temperature +20°C are shown below. However, in each table, the leftmost number represents the order from the object side, and f represents the focal length of the entire system. Furthermore, the first, second, and third lenses of the lens group G of each embodiment, Lo, Li! , 1-+ff each temperature (+20℃,
-10℃, +50℃) refractive index, temperature dispersion number W0
, Atsube number is also shown.

Table 1 (First Example) f = 75. OQO~150. QOO, angle of view 33.1
"～16.OF number 3.6 Table 2 (1st example) However, nth (+20'C) - 1fth = 103
．． 016 (1) f, #, =1.374(2) I
fz /f, l =0.471(3) f
, /[@ =1.173(4) f, /f1
．． l = 1.270(8) f/flt-
1s-0,212 Table 3 (Second Example) Table 4 (Second Example) n+4 (-10°C) -11,i (+50°C) fl
iFu122.189 (1) fl /f@ -1499 (2), 1
ft/f, l =0.459(3) r,
7'r, =1.166(4) f, #w -1
,361 (8) r/f+z-13=0.194 table (
3rd example) f = 81.500 to 200.000, angle of view 30.5
@~12.1” F number 4.6 Table 6 (3rd example) However, nth (→-20℃1-1Wth ζ□ n+t (-10℃) n+! (+50℃) fth = 1
22.220 (1) [1/f, 4-1.5QO (2) l f, /fW l -0,459
(3) E3/rw = 1.169 (4)
f, /f,1 = 1.361 (8) f /f
lz-13-0,223 Table 7 (4th example) f -81,500 to 200.000, angle of view 3o, 5
° ~ 12.12F number 4.6 Table 8 (4th example) However, nth (+20°C) - 1fth = 122°189° (1) f, /f, = 1.499 (2) l rt /rw l =0.549
(3) f3 /fW = 1.156 (4)
r4/rw =1.374(8) r/f
+t-+i=0.203 In the Luns group G of the first to fourth embodiments, the second lens I-+z is polymethyl methacrylate, and the third lens LI! uses polycarbonate. (W
)? Figure 2 shows various aberration diagrams for the 5.00 (bs, (M) 106,066 m and (T) 150.000 fins, and the reference temperature +20°C (t), -10°C 1.t
Fig. 3 shows the changes in the focal plane and spherical aberration due to zooming at +50°C (t2) and +50°C (t2), where the vertical axis is the F number and the horizontal axis is the Gaussian image plane at the reference temperature +20°C. represents the amount of defocus.

(W) at reference temperature +20°C of the second example 81,50
0 crane, (M) 145.500 crane and (T) 200.
Figure 5 shows various aberration diagrams for 000 Tsuru, and the reference temperatures +20'C (t), -10°C (t,) and +50°C.
FIG. 6 shows changes in the focal plane and spherical aberration due to zooming at (1g).

(W) at reference temperature +20°C of 3rd example 81,50
0”-(M) 145,500 Soybean and (T) 200
Figure 8 shows various aberration diagrams at ,000 m.
Reference temperature 20℃ (t), -10℃ (1+) and +50
FIG. 9 shows changes in the focal plane and spherical aberration due to zooming at °C (t□).

(W) at reference temperature +20°C of 4th example 81.50
0 crane, (M) 145.200 m and (T) 200
．． FIG. 11 shows various aberration diagrams for the 000 Tsuru. Also,
Reference temperature 20℃ (t), -10℃ (tl) and +50
FIG. 12 shows changes in the focal plane and spherical aberration due to zooming at °C (t).

Each aberration diagram and the diagram showing changes in focal plane and spherical aberration due to zooming are based on the d-line (λ=587.6n+
*) In addition, the spherical aberration in the various aberration diagrams in Figures 2, 5, 8, and 11 is also shown for the g-line (λ = 435° 8 nm) to indicate chromatic aberration. .

From the figure, it is clear that in each example, the movement of the focal plane due to temperature and the fluctuation of the focal plane during zooming are sufficiently corrected, and good imaging performance is maintained over the entire magnification range. be.

(Effects of the Invention) As described above, the present invention makes it possible to reduce the weight of the zoom lens by using a plastic lens in the lens group G, and also to perform quick focusing, so that it can be used as an AF lens. Can be used. Furthermore, since it is possible to sufficiently suppress the influence of the temperature of the plastic lens, it is possible to obtain a telephoto zoom lens that can maintain good imaging performance over the entire zoom range.

[Brief explanation of the drawing]

FIG. 1 is a wide-angle optical path diagram of the first embodiment of the present invention. FIG. 4 is a wide-side optical path diagram of the second embodiment of the present invention. FIG. 7 is a wide-side optical path diagram of the third embodiment of the present invention;
FIG. 10 is a wide-side optical path diagram of the fourth embodiment of the present invention. Figures 2, 5, 8 and m are the first diagrams according to the present invention.
Various aberration diagrams, z-3, 6, 9, and axial diagrams of the embodiment, the 2nd embodiment, the 3rd embodiment, and the 4th embodiment correspond to the 1st embodiment, the 2nd embodiment according to the present invention. FIG. 4 is a diagram showing the variation of spherical aberration due to zooming at reference temperatures of +20° C. (1), -10° C. (t, ), and +50° C. (1) in Example, Third Example, and Fourth Example. (Explanation of symbols of main parts) G+... 1st lens group G, 2nd lens group G3... 3rd lens group G4... 4th lens group

Claims (1)

[Claims] 1. In order from the object side, a first lens group G_1 that has positive refractive power and performs focusing, and a variator that performs magnification change by moving along the optical axis and has negative refractive power. A second lens group G_2, a third lens group G_3 which is a compensator that has a positive refractive power and keeps the position of the image plane that changes due to the movement of the variator constant, and a third lens group G_3 that has a positive refractive power and has an imaging function. The fourth lens group G, which is a relay system, has
_4, and the first lens group G_1 includes a plastic lens. 2. The zoom lens according to claim 1, wherein the telephoto zoom lens satisfies the following conditions. (1) 1.0<f_1/f_W<2.5 (2) 0.35<|f_2/f_W|<0.55(3)
0.8<f_3/f_W<1.5 (4) 1.0<f_4/f_W<1.6 f_1: Focal length of the first lens group G_1. f_2: Focal length of the second lens group G_2. f_3: Focal length of the third lens group G_3. f_4: Focal length of the fourth lens group G_4. 3 The first lens group G_1 includes, in order from the object side, a positive lens L_1_1, a positive lens L_1_2, and the positive lens L.
The positive lens L_1_2 and the negative lens L_1_3 are made of plastic lenses, and the refractive index of the i-th lens component of the first group is set at temperatures t, t_1, t_2. When n_1_i(t), n_1_i(t_1), n_1_i
(t_2), the temperature dispersion W_1_i of the material forming the i-th lens component of the first group is W_1_i=[n_1_i(t)-1]/[n_1_i
(t_1)-n_1_i(t_2)] However, t_1<t
The telephoto zoom lens according to claim 2, wherein the telephoto zoom lens is defined as <t_2 and satisfies the following conditions. (5) [△P_1/√(f_W・f_T)](β_T^
2-β_W^2)<0.03(6)[△P_1/√(f
_W・f_T)] [β_T/β_W]^2<0.05(
7) -0.2<f_1_2_-_1_3 [1/(f_1_2
ν_1_2)+1/(f_1_3ν_1_3)]<-0
．． 02(8)0.1<f/f_1_2_-_1_3<0
．． 5 However, △P_1=｜Σ＾3_i_=_1(h_1_i^2)/
(f_1_iW_1_i) | f_1_i: Focal length at temperature t of the i-th lens component of the first group in order from the object side. h_1_i: The height of incidence of a paraxial ray that enters from the object side at a height h into the i-th lens component of the first group. f_W: Focal length of the entire system at the wide end. f_T: Focal length of the entire system at the telephoto end. β_W: Combined magnification of the second to fourth lens groups at the wide end. β_T: Combined magnification of the second to fourth lens groups at the telephoto end. ν_1_2: Second lens L_1 in the first lens group G_1
Abbe number of _2. ν_1_3: Third lens L_1 in the first lens group G_1
Abbe number of _3. f_1_2_-_1_3: the second lens in the first lens group G_1
Synthetic focal length of the cemented lens of lens L_1_2 and third lens L_1_3.