JPS5865407A - Zoom lens system - Google Patents

Abstract

PURPOSE:To make the movement of a focus by a change in temp. small in a zoom lens having a variable magnification part and a master part and consisting essentially of lenses made of org. glass, by constituting at least one piece of the positive lenses forming the master part of inorg. glass. CONSTITUTION:In a zoom lens system consisting of the positive 1st group G1 as a focusing group, the negative 2nd group G2 as a variate, the positive 3rd group as a compensator, and the positive 4th group G4 as a master part successively from the object side, the 1st-3rd groups constitute the variable magnification part. The 1st-3rd groups are constituted of lenses L1, L6 consisiting of polystyrene and lenses L2-L5, L7 consisting of acrylics, and the 4th group G4 is constituted of a lens L8 consisting of inorg. glass, a lens L9 consisting of polystyrene, and lenses L10, L11 consisting of acrylics. Since the lens L8 is constituted of inorg. glass, the movement of the focus by a change in temp. is made small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens consisting of a so-called plastic lens made of organic glass, and particularly to an improvement of a zoom lens system having a variable power section and a master section.

In various lens systems, if all the lenses as constituent elements were replaced with organic glass lenses called plastic lenses, the weight would be 173 to 1/2, resulting in a significant weight reduction and 1; Cost can be reduced. However, plastic has a larger expansion coefficient than glass, and the refractive index changes by 4 degrees.
Since the temperature is large, there is a drawback that the focal plane of the lens moves due to a change in temperature C2.

To improve this drawback, two fixed focus lenses with triplet configuration are used, one of the positive lenses is made of T glass, the other is made of low dispersion plastic, and the negative lens is made of high dispersion plastic to correct chromatic aberration. The technology for erasing the am change is disclosed in Japanese Patent Application Laid-open No. 55-14 by the same applicant as the present application.
It is known from Publication No. 3518 52.

In this Japanese Patent Application Laid-Open No. 55-143518, for a fixed focus lens system consisting of N lenses including a plastic lens, the first lens is kLi when the composite focal length of the lens system is 'kf', and the temperature t1 u puteru L
The focal length of l is /i, the incident height rhj of a paraxial ray incident on the lens Li at a height f from the object world side, and the refractive index of the lens L1 at 1 degree t is (t). Temperature dispersion '1 for the constituent materials! L+W, 4: and 1. (Defined as 1 < 1° and set it as t"am erasure condition". Then, from this, pal
! tt and 1. Regarding the two points, the amount of focus movement due to IL[ becomes zero.

However, this is only the case when a fixed focus lens is used, and when there are four zoom lenses, the focal position changes significantly between the shortest and longest focal length states. For example, focus at the longest focal length state and then focus at the shortest state 1.
= When zooming, even if the object is in focus at room temperature, Cm will be out of focus at high or low temperatures.

The object of the present invention is to provide a zoom lens system using a so-called plastic lens made of organic glass, which has all the advantages of a plastic lens, and also has practically sufficient correction of chromatic aberration! To provide a zoom lens system having a relatively simple structure, in which the focal position is practically sufficiently corrected over the entire magnification range during zooming even when there is a large change in a degree while maintaining ik.

A basic proposal for a zoom lens system that achieved the above purpose was previously filed by the applicant (1986-5).
No. 9685), it is mainly used for the purpose of correcting changes in the focal plane during zooming C2. At least one lens among the lens elements was composed of inorganic glass. This is zoom magnification 6
This is effective for zoom lenses with large zoom magnifications, but for zoom lenses with small zoom magnifications as low as 3 zoom magnifications, the change in focus due to the change in a degree that occurs in the variable magnification section may not be as large. In such a case, correction can be made by correcting the magnification system [omittedly, controlling only the OKR component of the master part to successfully bring it close to θ, and dividing the positive and negative t's. In this case, the focal plane may fluctuate during zooming depending on the degree of use, but if the amount is kept within the vicinity of focus #I, there is no endorsement.

The present invention provides a zoom lens having a variable power section and a master section, in which at least one positive lens in the master lens section is made of inorganic glass, thereby performing temperature correction only with the master section. It is.

In order to balance the focus fluctuation, the master lens section is set to 1 to cancel the IIR component t generated in the variable magnification section;
must be configured.

Of course, it is necessary to properly correct not only the AM aberration but also the chromatic aberration, and the most important point of the present invention is to control the degree aberration while correcting the chromatic aberration. Furthermore, it is also necessary to maintain power as part of the master. Focal lengths tfl, f1 .of each lens constituting part of the master.・・・・・・ft・・・・・・/be%
Lens aW1 fractional number 'lf wl, 92 @ ”
``'Vll11.?,, yk, height of paraxial ray passing through each lens t b> e hl,...k
If l...hj, @ for part of the master
Longitudinal aberration coefficient Tm.

The chromatic aberration Cm and the power (refractive power) Pm are, respectively!
I appear.

Master part power Pm k A certain value: While maintaining chromatic aberration Cm% @ Fjt Aberration coefficient Tm k Mutual 6: It is necessary to perform balanced correction, and zooming from the short focal length end to the long focal length end Junior high school 1 - It is necessary to balance the temperature so that it does not change too much. There are two aberration coefficients aT in the temperature of the variable magnification section. With the 3x zoom lens shown as GA, when the reference temperature gILt = 20C, between low @t, = -10C and @iit, = 50C, Tma (W) -0,00759° at the long focal length end. Then Tma(T)-0,02413 and the difference 0.0165
4 changes were observed. Variables of the master lens (curvature, interplanar spacing, power arrangement, etc.) [Change it in various ways] From the sense 2, the fluctuation component cannot be eliminated, but Oz: bringing it closer or dividing it into positive and negative C: more substantial harm can be reduced. This balance is different from the balance performed with a fixed focal length lens, and may result in the Tm value being reversed in the negative direction C: at the short focal length end. If the power is 1 and the power is 0, then when the entire zooming is completed, the positive and negative values will be balanced.

In the present invention, low @ t, 3-10 C and ^ temperature t,
= 50 C, it is desirable that the 1lLIiL aberration coefficient of the master part falls within the range mt -0,02≦Tm≦0.01 (4) as the standard 11[[20C, and in this case, f of all lens systems
The f1 degree aberration coefficient T tot is at the shortest focal length state, I Ttol (W) l≦0.01 (5)
At the longest focal length state, o, o o s≦Ttot (T)≦o, o a
It would be better to configure it so that (6) is achieved.

All lenses f elements in the lens system [When constructed with organic glass, the entire system has positive refractive power, so the temperature aberration coefficient of the entire system is necessarily a positive cage t-N, and if it is a zoom lens, f[
have.

Organic glass 12 that forms part of the zoom lens master
1. Comparing the individual 11 degree aberration coefficients and the [[ component of the a degree aberration coefficient of the entire system, the coefficient value of the combination of one or more lenses in the master part is almost equal to the DC component of the entire system. If the lens element is replaced with an inorganic glass, it is possible to correct the II DC component, but as a result, the aberration coefficient TmO value of the master part should be within the range of equation (4) 1 = Therefore, the zoom This enables efficient AF aberration correction for the entire lens system. If the lower limit of equation (4) is exceeded, [r
If the IL component is over-corrected and exceeds the upper limit, it is under-corrected, and it is necessary to correct the accompanying temperature aberration fluctuations to a practically sufficient value - Part 1. And the entire system 12) a.
As expressed by the condition of equation (5), the f aberration coefficient Ttot is a negative or positive value at the zero center C2 in the shortest focal length state, and as expressed by the condition of equation (6), it is a negative or positive value for the maximum focal length state. Therefore, it is optimal for the zoom lens to have a slightly large positive value for longitudinal aberration correction. If these conditions are not satisfied, the balance of llK aberrations will be disrupted and deterioration of the image will be unavoidable.

Furthermore, in the present invention 5, the master part C; provided with an inorganic glass lens (4 = 4 = its Atsube number ν in order to effectively correct the chromatic aberration as shown in equation (2) above);
It is desirable that d is νd>50. In addition, organic glass lenses with large refractive power have a large inherent AM aberration coefficient, so in order to correct the positive DC component of the sI & aberration coefficient that occurs in the entire system (; indicates the refractive power from O in the master part). The positive lens element is advantageously made of inorganic glass.

Below 5: Examples of the present invention will be described.

The first embodiment of the present invention is basically a four-group zoom lens, and its configuration is as shown in FIG. 1st group G1. Negative 2nd group G as a variator, positive 3rd group Gj as a compensator, positive 4th group GmkN as part of the master, zoom ratio 3, F number 1
．． 8C) It is a zoom lens system. Here, the first evaluation, the second evaluation, and the 1m3 area constitute the variable magnification section. And the first group G
, is a negative lens L made of polystyrene P-, and a positive lens L made of acrylic (PMM) bonded to this.
8. Furthermore, it is composed of a positive lens L Hatake that is similar to acrylic.
The second detail G is a negative lens L6 made of acrylic, and a negative lens LI made of acrylic.

This is composed of a positive lens L made of bonded polystyrene, and the third detail G is a positive lens L made of acrylic!
It's okay. The master part of the relay system has the fourth detail G, the positive lens L made of inorganic glass, the negative lens L made of polystyrene, and the two O correct lenses IJI@ made of acrylic.
It is composed of e 1711. In Diagram 1, the inorganic glass-like lenses are indicated by diagonal lines.

1II1111! The specifications of Example jII are shown in Table 14 below.
In the table, 4- indicates the Oam dispersion number of each lens element.

This @ degree dispersion number Wl is the standard am! t=zoc.

This is the value measured at low at, ==-1oc, and high alt, -5oc.

In the first embodiment, before correction of a longitudinal aberration, that is, 1
g8 lens L, [When formed of acrylic and all lens elements are made of organic glass, the temperature aberration coefficient of the entire system is Ttot (W) = 0.039 at the shortest focal length state.
81, Ttot (T) = 0 in the longest focal length state
．． 0565, which is a significantly large value. Therefore, in this embodiment, the 8th lens L is made of t-inorganic glass, and as a result, the temperature aberration coefficient of the 4th lens group as part of the master ranges from 1mm O, 0Ba84 before correction to 1"0 It becomes small as .00017, and T1° for the whole system.
(W) = 0.00684. 'r,. t(T)-0
, 02353, and the fluctuation component [cannot be removed, but it can be made to a fairly small value.

The optical aberration t#12 of the first embodiment is shown in FIG.

No. 29 (- indicates the shortest focal length state, (b) indicates the intermediate focal length state, (C) indicates the longest focal length state IIt, 8ph indicates spherical aberration, Ml indicates astigmatism, and Dim indicates distortion aberration,
d-line (A-587, 6) [Use the reference wavelength with tea (1-436, 8fi) as a reference wavelength to correct chromatic aberration. The third factor is an aberration diagram of an example in which the 1Ljf aberration is corrected, and FIG. 4 is an aberration diagram of an example in which the 1Ljf aberration is corrected. It is an aberration diagram when the fourth group Gak is entirely composed of organic glass. In each figure, (crow) shows the shortest focal length state, (b) shows the intermediate focal length state, and (C) shows the longest focal length state, sph is spherical aberration, Al is astigmatism, and D
lm is distortion aberration.

In addition, the reference af't20c and L, -10CC) are shown in the low temperature state ktt and the high temperature state 12t of 50C, respectively. From these temperature aberration diagrams, it is clear that the zoom lens of this example exhibits little fluctuation in focal position in response to large temperature changes from 110C to 50C, and maintains a practically sufficient imaging performance mt. be.

In the first embodiment described above, one inorganic glass corrective lens was used for the master part c, but another positive lens [made of inorganic glass C; can do. 4: This is an example of a zoom lens using two inorganic glass lenses in the master part, or the second embodiment. In the second embodiment, as shown in FIG. 5, the iris 8 lens L, which was an inorganic glass lens in the JIII embodiment described above, (in addition to the knee, the first lens L, which is the positive lens closest to the image side) is also used. It is made of inorganic glass.

If the lens closest to the image side is made of inorganic glass, the internal organic glass lens can be preserved.The specifications of the second embodiment are shown in Table 2 below.

In this second implementation, the atom coefficient of part of the master is Tm=-
The negative value is 0,01333, and the total system Il & aberration coefficient tit A & t in the short focal length state. 1(W)=-0,
00686, Ttol (T) = at maximum focal length
It becomes 0.00983. The value of each temperature aberration coefficient is the i! The values are shown in Table 3 below together with the values of Examples.

Table 3 Figure 6 1 shows how the temperature aberration coefficient value for the entire system changes as the magnification changes. Diagram 6 has the vertical axis 1: @degree aberration coefficient Ttot of the entire system * horizontal axis 1: focal length t of the entire system, and the left end is the shortest focal length (Wide).
), the right end represents the longest focal length 1f(Tel・)vt In the figure, - line 1 is before correction, the curve is the first embodiment, track 11
c shows the characteristics of each state in the second embodiment. r! jA
As shown, in the first and second embodiments, although the variation component due to the variable magnification C: is not removed, the absolute value of SOO is considerably small, and as can be seen from %lnyC In the example, the aberration coefficient becomes zero during zooming, and it is clear that the absolute value of the aberration coefficient is corrected to be extremely small over the entire zoom range.

The ray aberration of the second embodiment is shown in FIG. 7 (and the temperature aberration is shown in FIG. 8. The display of each aberration is the same as in FIGS. 2 and 3 for the first embodiment, @ before thermal aberration correction
The construction of the roof is shown in Figure 4. From the comparison of each aberration diagram,
It is clear that not only the ray aberration but also the 1 degree change from -10C to 50C, the AF aberration is corrected sufficiently well for practical use. Characteristic curve.

cO effectiveness is supported.

As described above, according to the present invention, only one or several lens elements are made of inorganic glass, and all other lens elements are made of plastic (organic glass).
It is possible to achieve a zoom lens in which the aK aberrations present in organic glass are sufficiently corrected for practical use over the entire zoom range. While maintaining the many advantages of plastic lenses, such as light weight, simple manufacturing, and low price, regarding the reference light beam:
This is an excellent zoom lens in which not only CO aberrations but also chromatic differences are corrected well enough for practical use, making it extremely useful.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a zoom lens according to a first example of the present invention;
Figure 2 is a diagram of the ray aberration of the first embodiment, where (black) shows the shortest focal length state, (b) shows the intermediate focal length state, and (c) shows the longest focal length state, and 89h shows the spherical aberration. indicates astigmatism, and Di indicates distortion. Figure 3 is an aberration diagram of the example in which AM aberration is corrected, and Figure 4 is an aberration diagram before @ rectilinearity correction. (a) is the shortest focal length state, (b) is the intermediate focal length state, (C) indicates the longest focal length lIt, 89 indicates spherical aberration, ML indicates astigmatism, and Dis indicates distortion aberration. Fig. 5 is a diagram of the configuration of the zoom lens of the second embodiment, and Fig. 6 shows the entire system. How the 111 degree aberration coefficient value changes with magnification,
FIG. 7 shows a ray aberration diagram of the second embodiment, and FIG. 8 shows a temperature aberration diagram of the second embodiment. [Explanation of symbols of main parts] L, Positive lens made of inorganic glass Lll Positive lens made of inorganic glass Application Artificial Nippon Kogaku Kogyo Co., Ltd. -0,500,5-〇800.5 hOt O'5 Ward 1 O6 Figure Wade City City 3r Chichi A3t+ -0,50α5 -0.500.!

Claims (1)

[Claims] In a zoom lens that has a variable power section and a master part and is mainly made of an organic glass lens, at least one positive lens of the positive lenses forming the master part is made of inorganic glass, and A zoom lens system characterized by correcting changes in focal position due to