JPH06273670A - Zoom lens using plastic lens - Google Patents

Abstract

PURPOSE:To provide the zoom lens which is compact and has aberrations satisfactorily corrected regardless of the use of plastic and has the aberration performance scarecely degraded by the temperatre change. CONSTITUTION:With respect to the zoom lens which consists of a first group having a negative refracting power and a second group having a positive refracting power in order from the object side and changes the focal length of the whole of the system by the change of the air gap between the first group and the second group, one or more plastic lenses are arranged in the first group or the second group, and refracting powers of respective groups and plastic lenses are properly prescribed. When the variance of aberrations due to the temperature change will be corrected, at least one gap between lenses is changed in accordance with the temperature change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a zoom lens using a plastic lens.

[0002]

2. Description of the Related Art At present, an optical system for a camera is being made compact and low in cost as well as being high in performance. Although there are several methods of achieving cost reduction, the method of using a plastic lens instead of the glass lens is extremely effective in significantly reducing the cost of the optical system.

The zoom lens targeted by the present invention is
It is composed of a first group having a negative refractive power and a second group having a positive refractive power in order from the object side. By changing the air space between the first group and the second group, It is a type that changes the focal length. In order to achieve compactness for this type of zoom lens, it is effective to increase the refractive power of each group to some extent. That is, by increasing the refracting power of the first group, the amount of movement of each group during zooming can be reduced, and by increasing the refracting power of the second group, the back focus can be shortened.

However, there are very few types of plastic lenses, and most of those currently used are those having a small refractive power such as polycarbonate and acrylic. For this reason, even if a plastic lens is used for a zoom lens that requires an excessively strong refractive power, the contribution of the plastic lens to the refractive power is small, and the advantage (cost reduction) of using the plastic lens is lost. Therefore, when using a plastic lens, it is necessary to properly define the refractive power of each group.

Further, as described above, since there are very few types of plastic lenses, their refractive index and dispersion are limited. Therefore, it is necessary to properly define the refractive power of each group also from the viewpoint of performing good aberration correction in an optical system using a plastic lens.

Further, the plastic lens has a larger change in shape and optical characteristics with respect to the temperature change than the glass lens. Therefore, in an optical system using a plastic lens, compared to an optical system made of only a glass lens,
Aberration performance may slightly deteriorate due to temperature change.

[0007]

SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide a zoom lens which is compact and has well-corrected aberrations even though plastic is used, and temperature. An object of the present invention is to provide a zoom lens with almost no deterioration in aberration performance due to changes.

[0008]

In order to achieve the above object, the present invention comprises, in order from the object side, a first group having a negative refractive power and a second group having a positive refractive power. In a zoom lens that changes the focal length of the entire system by changing the air space between the first group and the second group, at least one plastic lens is arranged in the first group or the second group, and The refractive power of each group and the refractive power of the plastic lens were properly defined.

Further, regarding the correction of the aberration variation due to the temperature change, the interval between the lenses at at least one place is changed according to the temperature change.

[0010]

With the above arrangement, the zoom lens according to the present invention is well corrected for aberrations, even though it is made of plastic, and the aberration performance is hardly deteriorated even when the temperature changes.

[0011]

EXAMPLES Examples of the present invention will be described in detail below. The zoom lens of the present invention comprises, in order from the object side, a first group having a negative refracting power and a second group having a positive refracting power, and an air gap between the first group and the second group is The focal length of the entire system is changed by changing it.

When a plastic lens is used for the first group of this zoom lens, it is necessary to satisfy the following conditional expression.

0.5 ≦ φW / φ1 ≦ 1.5 (1) 1.5 ≦ φ1 / φP1 ≦ 4.0 (2) where φW is the total system at the wide end Refractive power,
φ1 is the refractive power of the first group, and φP1 is the refractive power of the plastic lens in the first group.

Conditional expression (1) appropriately defines the refractive power of the first lens group with respect to the refractive power of the entire system at the wide end. When the lower limit of conditional expression (1) is exceeded and the refractive power of the first lens unit becomes strong, the distortion aberration generated in the first lens unit becomes too large, which makes correction particularly on the wide side difficult. On the contrary, when the upper limit of conditional expression (1) is exceeded and the refracting power of the first group becomes weak, the moving amount of each group during zooming increases, and the diameter of the first group becomes large in order to secure the ambient illuminance. Therefore, it becomes difficult to achieve compactness.

Conditional expression (2) appropriately defines the refractive power of the plastic lens in the first group with respect to the refractive power of the first group. Since the plastic lens has a weaker refractive power than the glass lens having the same curvature, it is necessary to increase the curvature in order to increase the refractive power. However, increasing the curvature means increasing the aberrations generated on that surface, which is disadvantageous for aberration correction. If the lower limit of conditional expression (2) is exceeded and the refractive power of the plastic lens becomes too strong, the amount of astigmatism generated at a high image height becomes large. On the contrary, if the upper limit of conditional expression (2) is exceeded and the refractive power of the plastic lens becomes too weak, it becomes difficult to correct chromatic aberration in a balanced manner.
Further, the fact that the refractive power of the plastic lens becomes small also means that the contribution of the plastic lens is made small, and the merit of using the plastic lens is reduced.

When a plastic lens is used for the second lens group, it is necessary to satisfy the following conditional expression.

0.5 ≤ φW / φ2 ≤ 1.5 (3) 0.5 ≤ φ2 / φP2 ≤ 1.3 (4) where φW is the total system at the wide end. Refractive power,
φ2 is the refracting power of the second group, and φP2 is the refracting power of the plastic lens in the second group.

Conditional expression (3) appropriately defines the refractive power of the second group with respect to the refractive power of the entire system at the wide end. When the lower limit of conditional expression (3) is exceeded and the refractive power of the second lens unit becomes too strong, it becomes difficult to correct coma. vice versa,
When the upper limit of the conditional expression (3) is exceeded and the refractive power of the second lens unit becomes too weak, the back focus becomes long and, as a result, the total length becomes long. Therefore, it is difficult to achieve compactness.

Conditional expression (4) appropriately defines the refractive power of the plastic lens in the second lens group with respect to the refractive power of the second lens group. If the lower limit of conditional expression (4) is exceeded and the refractive power of the plastic lens becomes strong, the curvature becomes too strong, and it becomes difficult to correct astigmatism and coma at a position where the image height is high. On the contrary, if the refractive power of the plastic lens becomes weaker than the upper limit of the conditional expression (4), it becomes difficult to correct chromatic aberration in a balanced manner. Also, conditional expression (2)
As described in connection with, the advantage of using a plastic lens is reduced.

Specific numerical examples of the zoom lens according to the present invention will be shown below. In each embodiment, the first lens group moves in a convex locus toward the image side, and the second lens group moves to the object side, in association with zooming from the wide side to the tele side. In each embodiment, f represents the focal length of the entire system, and ri (i = 1, 2,
(3, ...) is the radius of curvature of the i-th surface counted from the object side,
di (i = 1,2,3, ...) is the i-th axial upper surface distance counted from the object side, Ni (i = 1,2,3, ...), νi (i = 1,2) ,
3, ...) respectively indicate the refractive index and the Abbe number for the d-line (λ = 587.6 nm) of the i-th lens counted from the object side. A surface with a radius of curvature marked with * is composed of an aspherical surface, and the aspherical shape is defined by the following formula. It should be noted that D (n) in the aspherical surface coefficient indicates 10 to the n-th power.

[0021]

[Equation 1]

<Example 1> f = 36.00 to 49.48 to 68.00 FNO. = 4.60 to 5.20 to 5.65 Radius of curvature, axial upper surface spacing Refractive index Abbe number r 1 81.457 d 1 1.800 N 1 1.67000 ν 1 57.07 r 2 14.391 d 2 6.150 r 3 * 58.411 d 3 3.450 N 2 1.58340 ν 2 30.23 r 4 * -441.721 d 4 22.644 to 12.140 to 4.500 r 5 * 14.878 d 5 6.480 N 3 1.58170 ν 3 69.75 r 6 -40.596 d 6 2.260 r 7 * -22.369 d 7 5.540 N 4 1.64769 ν 4 31.23 r 8 * 2849.165 [aspherical coefficient] r 3 r 4 ε = 1.0000 ε = 1.0000 A 4 = -0.29114338 XD (-4) A 4 = -0.51700237 XD (-4) A 6 = -0.25793328 XD (-6) A 6 = -0.18191343 XD (-6) A 8 = -0.14775633 XD (-8) A 8 = -0.63340186 XD (-8) A10 = -0.14274627 XD (-11) A10 = 0.84984531 XD (-10) A12 = 0.12825186 XD (-12) A12 = -0.30603375 XD (-12) r 5 r 7 ε = 1.0000 ε = 1.0000 A 4 = -0.12358984 XD (-4) A 4 = 0.13073711 XD (-3 ) A 6 = -0.20375333 XD (-6) A 6 = 0.11324320 XD (-6) A 8 = -0.25961937 XD (-8) A 8 = -0.54826460 XD (-8) A10 = 0.44069158 XD (-10) A10 = 0.25889916 XD (-10) A12 = -0.1 2869138 XD (-12) A12 = -0.48251912 XD (-12) r 8 ε = 1.0000 A 4 = 0.18698392 XD (-3) A 6 = 0.34347145 XD (-6) A 8 = 0.22651399 XD (-8) A10 =- 0.18648502 XD (-10) A12 = -0.65375586 XD (-12).

<Example 2> f = 36.00 to 49.48 to 68.00 FNO. = 4.60 to 5.20 to 5.65 Radius of curvature Axial upper surface distance Refractive index Abbe number r 1 72.191 d 1 1.800 N 1 1.67000 ν 1 57.07 r 2 15.909 d 2 6.150 r 3 * 50.680 d 3 3.450 N 2 1.58340 ν 2 30.23 r 4 * 560.881 d 4 18.665 to 9.254 to 1.500 r 5 Aperture d 5 9.000 to 5.000 to 3.000 r 6 * 15.139 d 6 6.480 N 3 1.58170 ν 3 69.75 r 7- 44.594 d 7 2.260 r 8 * -22.281 d 8 5.540 N 4 1.64769 ν 4 31.23 r 9 * -8890.469 [aspherical surface coefficient] r 3 r 4 ε = 1.0000 ε = 1.0000 A 4 = -0.29818171 XD (-4) A 4 = -0.49259616 XD (-4) A 6 = -0.23531751 XD (-6) A 6 = -0.13283334 XD (-6) A 8 = -0.12656226 XD (-8) A 8 = -0.60673726 XD (-8) A10 = -0.92096094 XD (-13) A10 = 0.86187484 XD (-10) A12 = 0.11799659 XD (-12) A12 = -0.32872287 XD (-12) r 6 r 8 ε = 1.0000 ε = 1.0000 A 4 = -0.11988549 XD (- 4) A 4 = 0.13682460 XD (-3) A 6 = -0.20060176 XD (-6) A 6 = 0.12432056 XD (-6) A 8 = -0.23076597 XD (-8) A 8 = -0.53664162 XD (-8) A10 = 0.43560272 X D (-10) A10 = 0.27686611 XD (-10) A12 = -0.15547158 XD (-12) A12 = -0.46348328 XD (-12) r 9 ε = 1.0000 A 4 = 0.18519764 XD (-3) A 6 = 0.32890814 XD (-6) A 8 = 0.22443346 XD (-8) A10 = -0.18561953 XD (-10) A12 = -0.64941570 XD (-12).

<Example 3> f = 36.00 to 49.48 to 68.00 FNO. = 4.60 to 5.20 to 5.65 Radius of curvature, axial upper surface spacing Refractive index Abbe number r 1 62.084 d 1 1.800 N 1 1.67000 ν 1 57.07 r 2 13.861 d 2 6.150 r 3 * 56.285 d 3 3.450 N 2 1.64769 ν 2 31.23 r 4 * 811.260 d 4 19.527 to 9.091 to 1.500 r 5 Aperture d 5 3.000 to 3.000 to 3.000 r 6 * 14.937 d 6 6.480 N 3 1.58170 ν 3 69.75 r 7- 46.705 d 7 2.260 r 8 * -22.291 d 8 5.540 N 4 1.58340 ν 4 30.23 r 9 * 2903.432 d 9 1.550 r10 Light-shielding plate [aspherical coefficient] r 3 r 4 ε = 1.0000 ε = 1.0000 A 4 = -0.29494649 XD ( -4) A 4 = -0.51128395 XD (-4) A 6 = -0.22026784 XD (-6) A 6 = -0.17774407 XD (-6) A 8 = -0.15638582 XD (-8) A 8 = -0.63508910 XD ( -8) A10 = -0.31429768 XD (-11) A10 = 0.83692650 XD (-10) A12 = 0.11779022 XD (-12) A12 = -0.32192583 XD (-12) r 6 r 8 ε = 1.0000 ε = 1.0000 A 4 = -0.68102499 XD (-5) A 4 = 0.11939560 XD (-3) A 6 = -0.16013731 XD (-6) A 6 = 0.84010497 XD (-7) A 8 = -0.25800419 XD (-8) A 8 = -0.568612 19 XD (-8) A10 = 0.44679908 XD (-10) A10 = 0.23225379 XD (-10) A12 = -0.11384349 XD (-12) A12 = -0.51038013 XD (-12) r 9 ε = 1.0000 A 4 = 0.18793482 XD (-3) A 6 = 0.34563309 XD (-6) A 8 = 0.22419967 XD (-8) A10 = -0.19084920 XD (-10) A12 = -0.66245962 XD (-12).

<Example 4> f = 36.00 to 49.48 to 68.00 FNO. = 4.60 to 5.20 to 5.65 Radius of curvature Axial upper surface spacing Refractive index Abbe number r 1 66.751 d 1 1.800 N 1 1.67000 ν 1 57.07 r 2 14.851 d 2 6.150 r 3 * 47.818 d 3 3.450 N 2 1.64769 ν 2 31.23 r 4 * 217.765 d 4 24.786 ~ 13.042 ~ 4.500 r 5 * 15.195 d 5 6.480 N 3 1.58170 ν 3 69.75 r 6 -47.158 d 6 2.260 r 7 * -22.054 d 7 5.540 N 4 1.58340 ν 4 30.23 r 8 * Light-shielding plate [aspherical coefficient] r 3 r 4 ε = 1.0000 ε = 1.0000 A 4 = -0.28262391 XD (-4) A 4 = -0.47756876 XD (-4) A 6 = -0.16137901 XD (-6) A 6 = -0.11026894 XD (-6) A 8 = -0.16200153 XD (-8) A 8 = -0.59048575 XD (-8) A10 = -0.18472748 XD (-11) A10 = 0.87539355 XD (-10) A12 = 0.18843086 XD (-12) A12 = -0.33549952 XD (-12) r 5 r 7 ε = 1.0000 ε = 1.0000 A 4 = -0.74608634 XD (-5) A 4 = 0.12439702 XD (-3 ) A 6 = -0.18086234 XD (-6) A 6 = 0.91749585 XD (-7) A 8 = -0.19026533 XD (-8) A 8 = -0.61034865 XD (-8) A10 = 0.46849927 XD (-10) A10 = 0.19939017 XD (-10) A12 = -0.1 4718683 XD (-12) A12 = -0.52854273 XD (-12) r 8 ε = 1.0000 A 4 = 0.18609478 XD (-3) A 6 = 0.30046564 XD (-6) A 8 = 0.20731721 XD (-8) A10 =- 0.20037646 XD (-10) A12 = -0.66577631 XD (-12).

<Example 5> f = 36.00 to 49.48 to 68.00 FNO. = 4.60 to 5.20 to 5.65 Radius of curvature Axial surface spacing Refractive index Abbe number r 1 61.363 d 1 1.800 N 1 1.67000 ν 1 57.07 r 2 14.085 d 2 6.150 r 3 * 60.400 d 3 3.450 N 2 1.58340 ν 2 30.23 r 4 * -1835.806 d 4 13.511 to 7.084 to 1.500 r 5 Aperture d 5 9.000 r 6 * 14.896 d 6 6.480 N 3 1.58170 ν 3 69.75 r 7 -47.429 d 7 2.260 r 8 * -22.500 d 8 5.540 N 4 1.58340 ν 4 30.23 r 9 * 1628.002 d 9 1.550 ~ 9.748 ~ 11.946 r10 Light shielding plate [aspherical coefficient] r 3 r 4 ε = 1.0000 ε = 1.0000 A 4 = -0.29229860 XD (-4) A 4 = -0.52445718 XD (-4) A 6 = -0.25703219 XD (-6) A 6 = -0.19694275 XD (-6) A 8 = -0.16613289 XD (-8) A 8 = -0.64418795 XD (-8) A10 = -0.30464407 XD (-11) A10 = 0.83206394 XD (-10) A12 = 0.11671135 XD (-12) A12 = -0.31826407 XD (-12) r 6 r 8 ε = 1.0000 ε = 1.0000 A 4 = -0.99548313 XD (-5) A 4 = 0.12344681 XD (-3) A 6 = -0.10854409 XD (-6) A 6 = 0.51979528 XD (-7) A 8 = -0.29249420 XD (-8) A 8 =- 0.5453 4387 XD (-8) A10 = 0.41892810 XD (-10) A10 = 0.26540607 XD (-10) A12 = -0.96706485 XD (-13) A12 = -0.48378692 XD (-12) r 9 ε = 1.0000 A 4 = 0.18835050 XD (-3) A 6 = 0.37772697 XD (-6) A 8 = 0.24099073 XD (-8) A10 = -0.17799959 XD (-10) A12 = -0.65146800 XD (-12).

<Example 6> f = 36.00 to 49.48 to 68.00 FNO. = 4.60 to 5.20 to 5.65 Radius of curvature Axial upper surface spacing Refractive index Abbe number r 1 79.070 d 1 1.800 N 1 1.67000 ν 1 57.07 r 2 13.963 d 2 6.150 r 3 * 52.311 d 3 3.450 N 2 1.58340 ν 2 30.23 r 4 * 1138.252 d 4 17.686 to 8.316 to 1.500 r 5 Aperture d 5 3.000 to 3.000 to 3.000 r 6 * 14.905 d 6 6.480 N 3 1.58170 ν 3 69.75 r 7- 43.204 d 7 2.260 r 8 * -22.089 d 8 5.540 N 4 1.58340 ν 4 30.23 r 9 * 3873.267 [aspherical surface coefficient] r 3 r 4 ε = 1.0000 ε = 1.0000 A 4 = -0.27802883 XD (-4) A 4 = -0.50999300 XD (-4) A 6 = -0.20187191 XD (-6) A 6 = -0.17473650 XD (-6) A 8 = -0.16798786 XD (-8) A 8 = -0.63208113 XD (-8) A10 =- 0.41959853 XD (-11) A10 = 0.84027562 XD (-10) A12 = 0.11893100 XD (-12) A12 = -0.32064012 XD (-12) r 6 r 8 ε = 1.0000 ε = 1.0000 A 4 = -0.91388942 XD (-5 ) A 4 = 0.12039996 XD (-3) A 6 = -0.17596690 XD (-6) A 6 = 0.56801253 XD (-7) A 8 = -0.22653953 XD (-8) A 8 = -0.59505621 XD (-8) A10 = 0.45460966 XD (-10) A10 = 0.22543220 XD (-10) A12 = -0.12685361 XD (-12) A12 = -0.50755362 XD (-12) r 9 ε = 1.0000 A 4 = 0.18756389 XD (-3) A 6 = 0.33134369 XD (-6) A 8 = 0.22109359 XD (-8) A10 = -0.18928160 XD (-10) A12 = -0.65443269 XD (-12).

Examples 1 and 2 are examples in which one plastic lens is used in the first group, Examples 3 and 4 are examples in which one plastic lens is used in the second group, and Example 5 6 is an example when one plastic lens is used for both the first and second groups.

When one plastic lens is used for the first lens group, the first lens group is a meniscus-shaped glass lens (first lens) having a negative refracting power with a convex surface facing the object side in order from the object side, and a positive lens. It is desirable that the lens be composed of two lenses, that is, a plastic lens (second lens) having a refractive power of. Here, the first lens is a negative meniscus lens for correcting distortion, and the glass lens is for giving a strong refracting power. Also, the second
It is the first that the lens is a positive plastic lens
This is because the Petzval sum within the group is reduced and chromatic aberration is corrected well. Further, from the viewpoint of correction for distortion and astigmatism, it is desirable to provide this plastic lens with an aspherical surface.

On the other hand, when one plastic lens is used for the second lens group, the second lens group has a positive refractive power glass lens (first lens) and a negative refractive power in order from the object side. It is desirable to use two plastic lenses (second lens). Here, the first lens is a positive lens for the purpose of correcting spherical aberration. Further, the first lens is a positive glass lens and the second lens is a negative plastic lens in order to satisfactorily correct chromatic aberration and astigmatism by selecting a glass type having a small dispersion as the first lens. Is. Further, the shape of the second lens on the image side is preferably a flat surface or a surface having a weak curvature with a concave surface facing the image side from the viewpoint of correction of astigmatism. Will be even easier.

When plastic lenses are provided in both the first and second groups, it is desirable that both the first and second groups satisfy the above-mentioned constitution.

Next, a description will be given, with reference to Examples 5 and 3, of a configuration for correcting aberration variation due to temperature change which may occur due to the use of a plastic lens.

First, a fifth embodiment in which one plastic lens is used for each of the first and second groups will be described. FIG. 13 is an aberration diagram of Example 5 at 20 ° C. As can be seen from the figure, each aberration is well corrected. on the other hand,
FIG. 14 is an aberration diagram of Example 5 at 50 ° C. However, only the plastic lens changes the curvature, core thickness, refractive index, and aspherical shape with respect to temperature changes.
This is because the fluctuation of the glass lens with respect to the temperature change can be almost ignored. Detailed data on changes in curvature, core thickness, refractive index, and aspherical shape of the plastic lens due to temperature change are omitted. From this figure, it can be seen that the spherical aberration has fallen under due to temperature changes.

In the present invention, this aberration change is corrected by changing the lens interval that does not contribute to zooming. Specifically, only the lens spacing of d2 in the first group, only the lens spacing of d7 in the second group, or both the lens spacings of d2 and d7 are changed according to the temperature. The amount of change in the lens interval is Δd2 = -0.12mm / 30 ° C when correcting only d2, and Δd when correcting only d7.
7 = -0.05mm / 30 ℃, Δ when correcting both d2 and d7
d2 = -0.05 mm / 30 ° C, Δd7 = -0.03 mm / 30 ° C. Aberration diagrams when these lens intervals are changed are shown in FIGS. From this figure, it can be seen that the aberration is well corrected, especially the spherical aberration is sufficiently corrected. The movement of the image point due to the temperature change may be corrected by focusing.

It is desirable that the amount of the lens interval changed to correct the aberration change due to the temperature change should satisfy the following conditional expression. │Σ (ΔSA (di) ・ Δdi) -ΔSA ｜ ≦ ｜ y '/ 10 ｜ ・ ・ ・ (5) ｜ Σ (ΔDS (di) ・ Δdi) -ΔDS ｜ ≦ ｜ y' / 10 ｜ ・ ・ ・ ( 6) | Σ (ΔDM (di) · Δdi) -ΔDM | ≦ | y '/ 10 | (7) where Δdi is the amount of change in the lens interval (di) when the temperature changes by 1 ° C. (Mm), ΔSA (di): Variation of spherical aberration at the zonal when the lens interval (di) is changed by 1 mm, ΔDS (di): Sagittal direction when the lens interval (di) is changed by 1 mm 0.8 Astigmatism variation in y ', ΔDM (di): Astigmatism variation in meridional direction 0.8y' when lens spacing (di) is changed by 1 mm, ΔSA: Temperature has changed by 1 ° C Variation of spherical aberration at the zonal of the plastic lens, ΔDS: variation of astigmatism in the sagittal direction 0.8y 'of the plastic lens when the temperature changes by 1 ° C, ΔDM: temperature of 1 Astigmatism variation of 0.8y 'in the meridional direction of the plastic lens when changed by ° C, y': Half the diagonal length of the screen.

When the upper limit values of the conditional expressions (5) to (7) are exceeded, the effect of correcting the aberration change is insufficient, or conversely, excessive correction is performed, which means that the lens interval is changed. Disappears. The suffix Σ takes into consideration the case where there are a plurality of lens intervals to be changed.

Furthermore, if correction of distortion, axial chromatic aberration, lateral chromatic aberration, etc. is taken into consideration, it is desirable that the following conditional expression be satisfied. │Σ (ΔAB (di) ・ Δdi) -ΔAB│ ≦ | y '/ 10 ｜ (8) where ΔAB (di): Arbitrary aberration when the lens interval (di) is changed by 1 mm ΔAB: fluctuation amount of arbitrary aberration of the plastic lens when the temperature changes by 1 ° C.

Similar to the conditional expressions (5) to (7), if the upper limit of the conditional expression (8) is exceeded, the effect of correcting the aberration change is insufficient, or conversely, excessive correction is performed. And
There is no point in changing the lens interval.

As for the lens interval changed to correct the aberration change, one position may be sufficient, or correction may be required at several positions. However, if the number of lens intervals to be changed is small, the mechanism for changing the lens intervals becomes simpler. Therefore, the above conditional expression (5)-
It is desirable to find the appropriate lens spacing using (8).

Next, a third embodiment in which one plastic lens is used only in the second lens group will be described. FIG.
Is an aberration diagram of Example 3 at 20 ° C., and FIG.
It is an aberration diagram at 0 ° C. The lens spacing changed to correct the aberration variation is the same as in the fifth embodiment described above, only the lens spacing of d2 in the first group and d7 in the second group.
Either only the lens spacing of d2 or d7 or both of these lens spacings. The amount of change in the lens interval is d
When only 2 is used for correction, Δd2 = -0.12mm / 30 ° C, when only d7 is used, Δd7 = -0.04mm / 30 ° C, when both d2 and d7 are used, Δd2 = -0.06mm / 30 ° C.・ Δd7 ＝ -0.0
It is 2mm / 30 ℃. Aberration diagrams when these lens intervals are changed are shown in FIGS. From this figure, it can be seen that the aberration is well corrected.

By using the lens spacing that is changed in order to correct the aberration variation due to the temperature change, it is possible to also correct the aberration variation that occurs during zooming or focusing. For example, in order to correct the aberration variation during zooming from wide to tele in the fifth embodiment, the lens spacing d2 or d7 may be changed as shown in the table below.

[0042] Further, in order to correct the aberration variation at the time of focusing to 2.0 m in the above-described fifth embodiment, the lens spacing d2 or d7 may be changed as shown in the table below.

[0043] FIG. 23 shows one embodiment of the mechanism for changing the lens interval. In this embodiment, it is possible to correct the aberration fluctuation that occurs during zooming, by using the lens spacing that is changed to correct the aberration fluctuation that accompanies the temperature change.
The temperature sensor (11) measures the temperature of the optical system itself or the outside of the optical system and outputs the temperature information to the arithmetic unit (12). On the other hand, the zoom encoder (13) detects the focal length information of the zoom lens (14) and outputs it to the calculation unit (12). The calculation unit (12) calculates the amount of change in the lens interval for correcting aberration fluctuations at the current temperature and focal length based on the input temperature information and focal length information, and outputs it to the drive unit (15). To do. The drive unit (15)
A predetermined lens interval is changed based on this lens interval change amount.

When the fluctuation of aberration caused during zooming is not corrected, it is possible to use a material having a predetermined coefficient of thermal expansion for the holding cylinder for holding the lens as a mechanism for changing the predetermined lens interval. is there. By doing so, the lens interval required for correcting the aberration variation due to the temperature change is naturally obtained by the thermal expansion of the material.

The values relating to the conditional expressions (1) to (4) in each embodiment are as follows.

As shown in [Table 1]

Yes, conditional expressions (5) to
The values for (7) are

It is as shown in [Table 2].

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

According to the structure of the present invention, it is possible to obtain a zoom lens in which aberration is well corrected and the aberration performance is hardly deteriorated by a temperature change even though plastic is used. It will be possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a lens corresponding to Example 1 of the present invention.

FIG. 2 is a configuration diagram of a lens corresponding to Example 2 of the present invention.

FIG. 3 is a configuration diagram of a lens corresponding to Example 3 of the present invention.

FIG. 4 is a configuration diagram of a lens corresponding to Example 4 of the present invention.

FIG. 5 is a configuration diagram of a lens corresponding to Example 5 of the present invention.

FIG. 6 is a configuration diagram of a lens corresponding to Example 6 of the present invention.

FIG. 7 is an aberration diagram of a lens corresponding to Example 1 of the present invention.

FIG. 8 is an aberration diagram of a lens corresponding to Example 2 of the present invention.

FIG. 9 is an aberration diagram of a lens corresponding to Example 3 of the present invention.

FIG. 10 is an aberration diagram of a lens corresponding to Example 4 of the present invention.

FIG. 11 is an aberration diagram of a lens corresponding to Example 5 of the present invention.

FIG. 12 is an aberration diagram of a lens corresponding to Example 6 of the present invention.

FIG. 13 is an aberration diagram of a lens corresponding to Example 5 of the present invention (temperature 20 ° C.).

FIG. 14 is an aberration diagram of a lens corresponding to Example 5 of the present invention (temperature: 50 ° C.).

FIG. 15 is an aberration diagram of a lens corresponding to Example 5 of the present invention (aberration correction at a temperature of 50 ° C. and an interval d2).

FIG. 16 is an aberration diagram of a lens corresponding to Example 5 of the present invention (aberration correction at a temperature of 50 ° C. and an interval d7).

FIG. 17 is an aberration diagram of a lens corresponding to Example 5 of the present invention (aberration correction at a temperature of 50 ° C. and an interval d2 · d7).

FIG. 18 is an aberration diagram of a lens corresponding to Example 3 of the present invention (temperature 20 ° C.).

FIG. 19 is an aberration diagram of a lens corresponding to Example 3 of the present invention (temperature 50 ° C.).

FIG. 20 is an aberration diagram of a lens corresponding to Example 3 of the present invention (aberration correction at a temperature of 50 ° C. and an interval d2).

FIG. 21 is an aberration diagram of a lens corresponding to Example 3 of the present invention (aberration correction at a temperature of 50 ° C. and an interval d7).

FIG. 22 is an aberration diagram of a lens corresponding to Example 3 of the present invention (aberration correction at a temperature of 50 ° C. and an interval d2 · d7).

FIG. 23 is a configuration diagram of an embodiment of a mechanism for changing the lens interval.

Claims (3)

[Claims] 1. A first group having negative refracting power and a second group having positive refracting power in order from the object side. The air gap between the first group and the second group is changed. Therefore, in the zoom lens which changes the focal length of the entire system, at least one plastic lens is arranged in the first lens group, and the following conditional expression is satisfied: 0.5 ≦ φW / φ1 ≤ 1.5 1.5 ≤ φ1 / φP1 ≤ 4.0 where φW is the refractive power of the entire system at the wide end, φ1 is the refractive power of the first group, and φP1 is the first group. It is the refractive power of the plastic lens inside. 2. A first group having a negative refractive power and a second group having a positive refractive power are arranged in order from the object side, and an air gap between the first group and the second group is changed. Thus, in a zoom lens that changes the focal length of the entire system, at least one plastic lens is arranged in the second lens group, and the following conditional expression is satisfied: 0.5 ≦ φW / φ2 ≦ 1.5 0.5 ≦ φ2 / φP2 ≦ 1.3 where φW is the refractive power of the entire system at the wide end, φ2 is the refractive power of the second group, and φP2 is the second group. It is the refractive power of the plastic lens inside. 3. A first group having negative refracting power and a second group having positive refracting power in order from the object side, wherein an air gap between the first group and the second group is changed. Therefore, in a zoom lens using a plastic lens that changes the focal length of the entire system, it is possible to correct aberration fluctuations due to temperature changes by changing the distance between at least one lens with temperature changes. And a zoom lens.