JP3033136B2 - Compact zoom lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens, and more particularly to a zoom lens used for a single-lens reflex camera or the like.

Conventional technology Currently, as a zoom lens for SLR cameras, 50mm
In place of the above lens, a lens having a zoom ratio of about 2 has become mainstream. Therefore, compact SLR cameras,
In order to achieve cost reduction, there is a demand for a compact and low cost lens of this type. To reduce the size of the lens system, including the amount of movement of the lens during zooming, it is necessary to increase the refractive power of each lens group. It can be said that the direction is to increase. On the other hand, for cost reduction, it is effective to reduce the number of lenses. Thus, the compactness and low cost of the lens system include many contradictory elements.

In order to reduce the size and cost, for example, Japanese Patent Application Laid-Open No. Sho 58-60717 and Japanese Patent Publication No. Sho 59-13003
JP-A-61-69015, JP-A-61-87117, JP-A-61-87118
And JP-A-1-210914 have been proposed. These zoom lenses are composed of two components, negative and positive, and use two or more aspheric surfaces.

Problems to be Solved by the Invention However, even with these zoom lenses, compactness and cost reduction cannot be fully achieved.

Therefore, in view of the situation in which aspherical surfaces can be produced at low cost due to recent remarkable technological advances such as plastic molding and glass molding, the present invention effectively uses aspherical surfaces to maintain high optical performance. It is another object of the present invention to provide a low-cost and compact zoom lens with a small number of lenses.

Means for Solving the Problems In order to achieve the above object, a zoom lens according to the present invention includes:
A zoom system comprising, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power, and changing the air distance between the front group and the rear group to change the focal length of the entire system. In the lens, the whole system has two or more aspherical surfaces,
In addition, the following conditional expression is satisfied.

Here, φ ₁ : refractive power of the front group φ _W : refractive power of the whole system at the wide-angle end.

As described above, in order to reduce the cost (reduction of the number of lenses) and compactness (reduction of the moving distance and the overall length) of the zoom lens, it is effective to increase the refractive power of each group and each lens. is there. In the present invention, if the refractive power satisfies the above conditional expression, the conventional focal length 35
2-10mm in total length for zoom lens of -70mm class
It is possible to shorten it. However, on the other hand, various aberrations are thereby deteriorated, and it is difficult to maintain the performance with only the spherical surface.

In the present invention, the refractive power of each group is strengthened to shorten the overall length, and the accompanying deterioration of various aberrations is suppressed by using many aspherical surfaces, thereby obtaining good performance. In the present invention, by using at least two aspherical surfaces, aberrations are corrected (performance is improved) while the size of the lens is reduced. Regarding the aspherical surface, for example, when an aspherical surface is used for the lens closest to the object in the rear group, it is effective to correct spherical aberration. Is effective in correcting the coma aberration. On the other hand, when an aspheric surface is used for the lens closest to the object in the front group,
This is effective for correcting distortion and curvature of field near the wide-angle end. As described above, by effectively using the aspherical surface, it is possible to increase the refractive power of each lens unit and each lens while maintaining the performance. As a result, the cost can be reduced by reducing the number of lenses, and the overall length and movement can be reduced. Compactness is achieved by reducing the amount.

The above conditional expression defines the ratio between the refractive power of the entire system at the wide-angle end and the refractive power of the front lens unit. The configuration satisfying the conditional expression includes the total lens length, the moving amount for zooming, and the back focus. This is effective for keeping the aberration correction state in a good balance.

If the upper limit of the conditional expression is exceeded, the refractive power of the front unit will be excessively large, and it will be difficult to correct various aberrations generated in the front unit, particularly the field curvature and distortion, even if an aspherical surface is used in the front unit. On the other hand, if the lower limit is exceeded, the tendency for downward coma to be generated around the screen becomes remarkable, and it becomes difficult to secure a sufficient back focus.

 It is preferable that the following conditional expression is further satisfied.

Here, φ ₂ is the refractive power of the rear group.

The conditional expression defines a ratio between the refractive power of the entire system and the refractive power of the rear unit at the wide-angle end. If the upper limit of the conditional expression is exceeded, the refractive power of the rear unit will be excessively large, and it will be difficult to correct various aberrations, particularly spherical aberration, occurring in the rear unit even if an aspherical surface is used in the rear unit. If the lower limit is exceeded, a downward tendency of coma aberration around the screen becomes remarkable.

The front group may be composed of two lenses, the rear group may be composed of three lenses, or the front group and the rear group may be composed of two lenses.

It is desirable that all the aspheric surfaces in the front group satisfy the following conditional expression.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
For any height y in the vertical direction of the optical axis where 0 <y <0.8Y _max , Here, N: refractive index of the aspherical object-side medium N ′: refractive index of the aspherical image-side medium X (y): aspherical surface shape X ₀ (y): aspherical reference spherical shape r: Reference radius of curvature of aspheric surface ε: Quadratic surface parameter A _i : Aspheric surface coefficient: Paraxial radius of curvature of aspheric surface It is.

If the upper limit of the conditional expression is exceeded, the positive distortion and the positive shift of the field curvature become large in the intermediate angle of view band from the wide-angle end to the intermediate focal length region. If the lower limit is exceeded, the negative distortion becomes large in the range from the intermediate focal length to the telephoto end. In addition, the negative shift of the field curvature becomes remarkable in the entire zoom range.

When a lens having both aspheric surfaces is used in the front group, it is preferable that one surface satisfies the following conditional expression and the other surface satisfies the following conditional expression.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
For any height y in the vertical direction of the optical axis where 0.8Y _max <y <Y _max , It is.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
For any height y in the vertical direction of the optical axis where 0.8Y _max <y <Y _max , It is.

In the front group, an aspherical surface that satisfies the conditional expression means that the negative refractive power becomes weaker (positive refractive power becomes stronger) toward the periphery. Thus, distortion near the wide-angle end is corrected. Further, at this time, the curvature of field is favorably corrected by using an aspherical surface that satisfies the conditional expression.

It is desirable that all the aspheric surfaces in the rear group satisfy the following conditional expression.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
For any height y in the vertical direction of the optical axis where 0 <y <0.7Y _max , It is.

When the value exceeds the upper limit of the conditional expression, the annular spherical aberration has a large negative value, and there is a problem of a shift of a focus position due to a stop-down. If the lower limit is exceeded, the spherical aberration correction effect on the annular luminous flux becomes excessive, and it becomes difficult to correct other aberrations and spherical aberration in a well-balanced manner. in this case,
The spherical aberration tends to be wavy.

When a lens having both aspheric surfaces is used in the rear group, it is desirable that one surface satisfies the following conditional expression and the other surface satisfies the following conditional expression.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
For any height y in the vertical direction of the optical axis where 0.7Y _max <y <Y _max , It is.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
For any height y in the vertical direction of the optical axis where 0.7Y _max <y <Y _max , It is.

In the rear group, an aspherical surface that satisfies the conditional expression means that the positive refractive power becomes weaker (negative refractive power becomes stronger) toward the periphery. The conditional expression is a condition for correcting the spherical aberration falling to the under side in the range of the third-order aberration region to the over side. At this time, on-axis light passing through a place far from the optical axis of the lens may be overcorrected and go to the over side. It is only necessary to introduce an aspheric surface having a higher positive refractive power (a lower negative refractive power) to the other surface.

Further, it is desirable that the deviation amount of the aspheric surface on the side satisfying the conditional expression from the reference spherical surface be larger than the deviation amount of the aspheric surface on the side satisfying the conditional expression from the reference spherical surface.

It is desirable that the front group and the rear group are configured to satisfy the following conditional expression.

Here, φ _T : refractive power of the whole system at the telephoto end β: zoom ratio where φ ₁ <0 β = φ _W / φ _T.

These are the total lens length, the amount of movement for zooming,
This is a condition for keeping the back focus and the correction state of various aberrations in a good balance.

When the lower limit of the conditional expression is exceeded, the Petzval sum takes a large negative value, the image plane remarkably falls in the positive direction, and the distortion at the wide-angle end takes a large positive value. In addition, if the upper limit is exceeded, it is necessary to take a large change in the interval between the front and rear groups due to zooming,
At the wide angle end, the distance between the front and rear groups is largely separated, which causes an increase in the overall length of the lens.

If the lower limit of the conditional expression is exceeded, it becomes difficult to keep the back focus at an appropriate value (at least 1.1 times the focal length at the wide-angle end) at the wide-angle end, and it becomes difficult to secure a space for disposing the mirror. . If the upper limit is exceeded, the amount of movement of the front group and the rear group due to zooming becomes excessive, which is disadvantageous in the lens barrel configuration.

In front of the front group of the zoom lens according to the present invention, behind the rear group,
Or, even if a lens system having almost no refractive power is added between the front group and the rear group, it does not depart from the gist of the present invention. As a lens system to be added, it is desirable that the absolute value of the refractive power is one third or less of the refractive power at the telephoto end of the entire system.

EXAMPLES Examples of the compact zoom lens according to the present invention will be described below.

However, in each embodiment, r _{1 to} r ₁₀ indicate the radius of curvature of the surface counted from the object side, d _{1 to} d ₉ indicate the axial top surface distance counted from the object side, and N _{1 to} N ₅ , ν _{1 to} ν Reference numeral ₅ denotes the refractive index and Abbe number of each lens counted from the object side with respect to d-line. F indicates the focal length of the entire system, and F _NO indicates the open F number.

Note that, in the examples, a surface marked with an asterisk (*) indicates a surface constituted by an aspheric surface, and is defined by an expression representing the surface shape (X (y)) of the aspheric surface. .

<Example 1> Aspherical coefficients _{r 4: ε = 0.97677 A 4} = -0.46960 × 10 -4 A 6 = 0.18970 × 10 -6 A 8 = -0.10218 × 10 -7 A 10 = 0.92120 × 10 -10 A 12 = 0.98648 × 10 - ¹³ r ₅ : ε = 0.13064 × 10 A ₄ = −0.44294 × 10 ⁻⁴ A ₆ = −0.32517 × 10 ⁻⁶ A ₈ = −0.63065 × 10 ⁻⁹ A ₁₀ = −0.74042 × 10 ⁻¹¹ A ₁₂ = −0.17854 × 10 ^-13 r ₇ : ε = 0.10010 × 10 A ₄ = 0.90729 × 10 ^-4 A ₆ = -0.14917 × 10 ^-6 A ₈ = -0.96660 × 10 ^-8 A ₁₀ = -0.61239 × 10 ^-10 A ₁₂ = −0.25320 × 10 ⁻¹² r ₈ : ε = 0.93899 A ₄ = −0.17872 × 10 ⁻³ A ₆ = 0.41747 × 10 ⁻⁶ A ₈ = 0.82935 × 10 ⁻⁸ A ₁₀ = −0.55 230 × 10 ⁻⁹ A ₁₂ = 0.96840 × 10 ^-11 <Example 2> Aspheric coefficient r ₄ : ε = 0.10000 × 10 A ₄ = -0.24751 × 10 ^-4 A ₆ = 0.71600 × 10 ^-8 A ₈ = -0.84637 × 10 ^-9 r ₅ : ε = 0.10000 × 10 A ₄ = -0.63349 × 10 ⁻⁴ A ₆ = −0.32364 × 10 ⁻⁶ A ₈ = −0.11035 × 10 ⁻⁷ r ₆ : ε = 0.10000 × 10 A ₄ = −0.67323 × 10 ⁻⁴ A ₆ = −0.76224 × 10 ⁻⁶ A ₈ = −0.18025 × 10 ⁻⁸ r ₇ : ε = 0.10000 × 10 A ₄ = 0.74134 × 10 ⁻⁴ A ₆ = −0.80597 × 10 ⁻⁶ A ₈ = 0.94950 × 10 ⁻⁸ r ₈ : ε = 0.10000 × 10 A ₄ = 0.13887 × 10 ⁻³ A ₆ = −0.21954 × 10 ⁻⁶ A ₈ = 0.55614 × 10 ⁻⁸ <Example 3> Aspheric coefficient r ₄ : ε = 0.97677 A ₄ = -0.31833 x 10 ^-4 A ₆ = 0.11552 x 10 ^-6 A ₈ = -0.38664 x 10 ^-8 A ₁₀ = 0.23753 x 10 ^-10 r ₅ : ε = 0.11687 x 10 A ₄ = -0.26050 x 10 ^-4 A ₆ = -0.73075 x 10 ^-8 A ₈ = -0.21403 x 10 ^-8 A ₁₀ = 0.11257 x 10 ^-10 r ₇ : e = 0.10098 x 10 A ₄ = 0.95703 x 10 ^{_{-4 A 6 = 0.11262 × 10 -6}} A 8 = -0.82765 × 10 -8 A 10 = -0.31146 × 10 -10 A 12 = -0.21000 × 10 -13 r 8: ε = 0.94743 A 4 = 0.15530 × 10 - ³ A ₆ = 0.51579 x 10 ^-6 A ₈ = 0.10239 x 10 ^-7 A ₁₀ = -0.55151 x 10 ^-9 A ₁₂ = 0.50000 x 10 ^-11 <Example 4> Aspheric coefficient r ₂ : ε = 0.14772 × 10 A ₄ = −0.19835 × 10 ⁻⁴ A ₆ = −0.66077 × 10 ⁻⁸ A ₈ = −0.91491 × 10 ⁻⁹ r ₅ : ε = 0.12911 × 10 A ₄ = − 0.19849 × 10 ⁻⁴ A ₆ = 0.59001 × 10 ⁻⁷ A ₈ = −0.14707 × 10 ⁻⁸ r ₇ : ε = 0.10000 × 10 A ₄ = 0.98005 × 10 ⁻⁵ A ₆ = −0.37611 × 10 ⁻⁶ A ₈ = −0.19401 × 10 ⁻⁸ r ₈ : ε = 0.10000 × 10 A ₄ = 0.66420 × 10 ⁻⁴ A ₆ = −0.35319 × 10 ⁻⁷ A ₈ = −0.11571 × 10 ⁻⁸ <Example 5> Aspherical coefficients _{r 1: ε = 0.92540 A 4} = -0.12025 × 10 -4 A 6 = 0.52533 × 10 -7 A 8 = -0.32581 × 10 -10 r 2: ε = 0.10000 × 10 A 4 = -0.14468 × 10 ^{_{-4 A 6 = 0.87723 × 10 -}} 7 A 8 = 0.78426 × 10 -9 r 3: ε = 0.33160 A 4 = -0.11960 × 10 -4 A 6 = 0.14748 × 10 -6 A 8 = 0.60246 × 10 -9 r ₄ : ε = 0.95585 A ₄ = -0.51352 x 10 ^-4 A ₆ = 0.13347 x 10 ^-6 A ₈ = -0.13437 x 10 ^-8 r ₅ : ε = 0.12368 x 10 A ₄ = -0.22771 x 10 ^-4 A ₆ = 0.36746 × 10 ⁻⁷ A ₈ = −0.12825 × 10 ⁻⁸ r ₆ : ε = −0.13009 × 10 A ₄ = 0.30913 × 10 ⁻⁴ A ₆ = 0.45464 × 10 ⁻⁷ A ₈ = −0.68843 × 10 ⁻⁹ r ₇ : ε = 0.26965 × 10 A ₄ = 0.15665 × 10 ^-3 A ₆ = -0.54318 × 10 ^-6 A ₈ = -0.17532 × 10 ^-7 r ₈ : ε = -0.21970 A ₄ = 0.19799 × 10 ^-3 A ₆ = 0.32779 × 10 ^-6 A ₈ = −0.57687 × 10 ^-8 <Example 6> Aspheric coefficient r ₂ : ε = 0.10000 x 10 A ₄ = -0.15505 x 10 ^-4 A ₆ = 0.83879 x 10 ^-7 A ₈ = -0.24 127 x 10 ^-8 A ₁₀ = 0.23757 x 10 ^-10 A ₁₂ =-0.80847 × 10 ^-13 r ₄ : ε = 0.10000 × 10 A ₄ = −0.11854 × 10 ^-4 A ₆ = 0.53054 × 10 ^-7 A ₈ = −0.14796 × 10 ^-8 A ₁₀ = 0.12514 × 10 ^-10 A ₁₂ = − 0.51061 × 10 ^-13 r ₅ : ε = 0.10000 × 10 A ₄ = −0.11644 × 10 ⁻⁵ A ₆ = 0.8535 × 10 ⁻⁷ A ₈ = −0.16456 × 10 ⁻⁸ A ₁₀ = 0.15146 × 10 ⁻¹⁰ A ₁₂ = −0.61958 × 10 ⁻¹³ r ₇ : ε = 0.10000 × 10 A ₄ = −0.22564 × 10 ⁻⁴ A ₆ = 0.28631 × 10 ⁻⁷ A ₈ = 0.40710 × 10 ⁻⁹ A ₁₀ = 0.94855 × 10 ⁻¹¹ A ₁₂ = 0.43296 × 10 ^-13 r ₈ : ε = 0.10000 × 10 A ₄ = 0.18334 × 10 ^-4 A ₆ = −0.55751 × 10 ^-7 A ₈ = 0.18495 × 10 ^-9 A ₁₀ = 0.20056 × 10 ^-10 A ₁₂ = 0.25087 × 10 ^-13 r ₉ : ε = 0.10000 × 10 A ₄ = −0.13083 × 10 ⁻⁴ A ₆ = −0.31645 × 10 ⁻⁶ A ₈ = 0.63373 × 10 ⁻⁹ A ₁₀ = −0.10362 × 10 ⁻¹¹ A ₁₂ = −0.26952 × 10 ⁻¹³ <Example 7> Aspheric coefficient r ₁ : ε = 0.10000 x 10 A ₄ = 0.58892 x 10 ^-5 A ₆ = 0.48505 x 10 ^-7 A ₈ = -0.38701 x 10 ^-9 A ₁₀ = 0.65002 x 10 ^-12 A ₁₂ =-0.22233 x 10 ^-15 r ₂ : ε = 0.10000 x 10 A ₄ = -0.94516 x 10 ^-5 A ₆ = 0.39665 x 10 ^-7 A ₈ = -0.21510 x 10 ^-10 A ₁₀ = -0.12936 x 10 ^-11 A ₁₂ =- 0.13875 × 10 ^-13 r ₄ : ε = 0.10 × 10 × 10 A ₄ = −0.78692 × 10 ⁻⁵ A ₆ = −0.22629 × 10 ⁻⁸ A ₈ = −0.77 105 × 10 ⁻⁹ A ₁₀ = 0.41977 × 10 ⁻¹¹ A ₁₂ = −0.84804 × 10 ⁻¹⁴ r ₅ : ε = 0.10000 × 10 A ₄ = −0.21705 × 10 ⁻⁶ A ₆ = −0.83224 × 10 ⁻⁸ A ₈ = −0.11419 × 10 ⁻⁹ A ₁₀ = −0.56839 × 10 ^{− 12} A ₁₂ = 0.66732 x 10 ^-14 r ₇ : ε = 0.10000 x 10 A ₄ = -0.97076 x 10 ^-5 A ₆ = -0.46 160 x 10 ^-7 A ₈ = 0.26689 x 10 ^-9 A ₁₀ = -0.15883 x 10 ^-11 A ₁₂ = 0.35263 x 10 ^-14 r ₈ : ε = 0.10000 x 10 A ₄ = 0.19211 x 10 ^-4 A ₆ = -0.35547 x 10 ^-7 A ₈ = -0.75079 x 10 ^-9 A ₁₀ =-0.23221 x 10 ^-11 A ₁₂ = 0.60653 × 10 ^-13 r ₉ : ε = 0.10000 x 10 A ₄ = -0.81788 x 10 ^-5 A ₆ = -0.67632 x 10 ^-7 A ₈ = -0.10159 x 10 ^-8 A ₁₀ = 0 . 42857 × 10 ^-12 A ₁₂ = 0.23794 × 10 ^-14 <Example 8> Aspheric coefficient r ₁ : ε = 0.10 × 10 A ₄ = −0.17314 × 10 ⁻⁴ A ₆ = −0.11099 × 10 ⁻⁶ A ₈ = 0.12451 × 10 ⁻⁸ A ₁₀ = −0.72864 × 10 ⁻¹¹ A ₁₂ = 0.26533 × 10 ^-13 r ₂ : ε = 0.10000 × 10 A ₄ = −0.23680 × 10 ⁻⁴ A ₆ = −0.15564 × 10 ⁻⁶ A ₈ = −0.11770 × 10 ⁻⁸ A ₁₀ = 0.69290 × 10 ⁻¹¹ A ₁₂ = 0.34891 × 10 ^-13 r ₄ : ε = 0.10000 × 10 A ₄ = −0.25119 × 10 ^-4 A ₆ = 0.34222 × 10 ^-7 A ₈ = −0.67319 × 10 ^-9 A ₁₀ = 0.37125 × 10 ^-11 A ₁₂ ＝ −0.20868 × 10 ⁻¹³ r ₅ : ε = 0.10 × 10 × 10 A ₄ = 0.20886 × 10 ⁻⁵ A ₆ = 0.65790 × 10 ⁻⁷ A ₈ = −0.64905 × 10 ⁻⁹ A ₁₀ = 0.65032 × 10 ⁻¹¹ A ₁₂ = −0.26549 × 10 ⁻¹³ r ₇ : ε = 0.10 × 10 × 10 A ₄ = −0.22551 × 10 ⁻⁴ A ₆ = 0.22428 × 10 ⁻⁷ A ₈ = 0.46396 × 10 ⁻⁹ A ₁₀ = 0.61312 × 10 ⁻¹¹ A ₁₂ = 0.56137 × 10 ^-13 r ₈ : ε = 0.10000 × 10 A ₄ = 0.24322 × 10 ^-4 A ₆ = 0.10926 × 10 ^-6 A ₈ = 0.11323 × 10 ^-8 A ₁₀ = 0.15914 × 10 ^-10 A ₁₂ = 0.14505 × 10 ^-12 r ₉ : ε = 0.10000 x 10 A ₄ = -0.31514 x 10 ^-5 A ₆ = -0.79866 x 10 ^-7 A ₈ = 0.86102 x 10 ^-9 A ₁₀ = 0.29418 x 10 ^-11 A ₁₂ = 0.7070 9 × 10 ^-14 <Example 9> Aspheric coefficient r ₁ : ε = 0.10000 x 10 A ₄ = 0.20109 x 10 ^-4 A ₆ = 0.13635 x 10 ^-6 A ₈ = 0.11051 x 10 ^-8 A ₁₀ = 0.43942 x 10 ^-13 A ₁₂ = -0.51481 x 10 ^-13 r ₂ : ε = 0.10000 x 10 A ₄ = 0.83021 x 10 ^-5 A ₆ = 0.33585 x 10 ^-6 A ₈ = 0.29980 x 10 ^-8 A ₁₀ = 0.26751 x 10 ^-10 A ₁₂ = 0.23205 x 10 ^-12 r ₃ : ε = 0.10000 x 10 A ₄ = -0.68916 x 10 ^-4 A ₆ = -0.12267 x 10 ^-6 A ₈ = 0.16 135 x 10 ^-8 A ₁₀ = 0.12568 x 10 ^-10 A ₁₂ = 0.72978 x 10 ^-13 _{r 4: ε = 0.10000 × 10} A 4 = -0.63114 × 10 -4 A 6 = -0.87244 × 10 -7 A 8 = 0.14728 × 10 -9 A 10 = 0.20899 × 10 -11 A 12 = -0.17228 × 10 - _{^{13 r 5: ε = 0.10000 ×}} 10 A 4 = -0.16890 × 10 -5 A 6 = 0.19098 × 10 -6 A 8 = -0.11329 × 10 -8 A 10 = 0.93460 × 10 -11 A 12 = 0.41743 × 10 - ¹³ r ₆ : ε = 0.10000 x 10 A ₄ = 0.24647 x 10 ^-4 A ₆ = 0.12879 x 10 ^-6 A ₈ = 0.45 128 x 10 ^-9 A ₁₀ = -0.11513 x 10 ^-10 A ₁₂ = 0.56075 x 10 ^-13 r ₇ : ε = 0.10000 x 10 A ₄ = 0.16088 x 10 ^-4 A ₆ = -0.13611 x 10 ^-6 A ₈ =-0.23345 x 10 ^-8 A ₁₀ =-0.26920 x 10 ^-10 A ₁₂ =-0.29101 x 10 ^-12 r ₈ : ε = 0.10000 x 10 A ₄ = 0.52549 x 10 ^-4 A ₆ = 0.19383 x 10 ^-6 A ₈ = -0.91899 x 10 ^-9 A ₁₀ = -0.43772 x 10 ^-11 A ₁₂ = 0.10395 x 10 ^-12 Fig. 1-Fig. 9 is a lens configuration diagram corresponding to the examples 1 to 9, most telephoto end arrows in the drawing widest angle end of the front group and rear group (S) ( The movement toward L) is schematically shown.

The first, second, and fourth embodiments each include, in order from the object side, a front lens unit including a negative meniscus lens concave on the image side and a second lens unit including a positive meniscus lens convex on the object side, and a biconvex lens. And a rear group consisting of a negative third lens and a biconcave negative fourth lens. In the first embodiment, the image-side surface of the second lens, the object-side surface of the third lens, and both surfaces of the fourth lens are aspherical. In the second embodiment, the image-side surface of the second lens and both surfaces of the third lens and the fourth lens are aspherical. In Example 4, the image-side surface of the first lens, the object-side surface of the third lens, and the fourth lens
Both surfaces of the lens are aspheric.

The third embodiment includes, in order from the object side, a front lens unit including a negative meniscus lens concave to the image side and a second lens unit including a positive meniscus lens convex to the object side, and a biconvex positive third lens. , A rear group consisting of a biconcave negative fourth lens and a fifth lens consisting of a positive meniscus lens convex on the object side. In Example 3, the image-side surface of the second lens, the object-side surface of the third lens, and both surfaces of the fourth lens are aspherical.

In the fifth embodiment, a front lens unit including a negative meniscus lens concave to the image side and a biconvex positive second lens in order from the object side, a biconvex positive third lens and a concave lens to the object side And a rear group composed of a fourth lens composed of a negative meniscus lens. In Example 5, both surfaces of all lenses are aspherical.

In the sixth embodiment, a front unit composed of a biconcave negative first lens and a biconvex positive second lens in order from the object side, a biconvex positive third lens, a biconcave negative fourth lens and And a rear group consisting of a fifth lens consisting of a positive meniscus lens convex on the image side. In Example 6, the image-side surface of the first lens, the image-side surface of the second lens, the object-side surface of the third lens, both surfaces of the fourth lens, and the object-side surface of the fifth lens are non- It is a spherical surface.

In the seventh embodiment, the front lens unit includes a first lens including a negative meniscus lens concave to the image side and a second lens including a positive meniscus lens convex to the object side, and a biconvex positive third lens. And a rear group consisting of a biconcave negative fourth lens and a fifth lens composed of a positive meniscus lens convex on the image side. In Example 7, both surfaces of the first lens, the image-side surface of the second lens, the object-side surface of the third lens, both surfaces of the fourth lens, and the object-side surface of the fifth lens are aspherical. .

In the eighth embodiment, a front lens unit composed of a negative meniscus lens concave to the image side and a biconvex positive second lens in order from the object side, a biconvex positive third lens, and a biconcave negative lens 4th of
Fifth lens and positive meniscus lens convex on the image side
And a rear group consisting of lenses. In Example 8, both surfaces of the first lens, the image-side surface of the second lens, the object-side surface of the third lens, both surfaces of the fourth lens, and the object-side surface of the fifth lens are aspherical. .

In the ninth embodiment, a front lens unit composed of a first lens composed of a negative meniscus lens concave on the image side and a second lens composed of a positive meniscus lens convex on the image side in order from the object side, and a biconvex positive third lens And a rear group consisting of a fourth lens consisting of a negative meniscus lens concave on the object side. still,
In Example 9, both surfaces of all lenses are aspherical.

10 to 18 are aberration diagrams corresponding to the first to ninth embodiments, wherein (S) is the focal length at the wide-angle end, (M) is the intermediate focal length, and (L) is the aberration at the telephoto end. Is shown. The solid line (d) represents the aberration with respect to the d-line, and the dotted line (SC) represents the sine condition. Further, a dotted line (DM) and a solid line (DS) represent astigmatism on the meridional surface and the sagittal surface, respectively.

Table 1 shows that in the conditional expressions in Examples 1 to 9, In the conditional expression Are shown respectively.

Table 2 shows that in the conditional expressions in Examples 1 to 9, And in the conditional expression Are shown respectively.

Tables 3 to 11 correspond to Examples 1 to 9, respectively.
In the conditional expression for each aspheric surface with respect to the value of y, Is represented by (I), and in the conditional expression Is represented by (II).

Effects of the Invention As described above, according to the present invention, a low-cost and compact zoom lens can be realized with a small number of lenses while maintaining high optical performance. Further, when the zoom lens according to the present invention is used for a single-lens reflex camera, the size and cost of the camera can be reduced.

[Brief description of the drawings]

FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8 and FIG.
10 is a lens configuration diagram corresponding to FIGS. FIG. 10, FIG. 11, FIG. 12, FIG. 13, FIG. 14, FIG.
FIGS. 16, 17, and 18 show Embodiment 1 of the present invention, respectively.
10 is an aberration diagram corresponding to FIGS.

Continuation of the front page (56) References JP-A-58-60717 (JP, A) JP-A-61-69015 (JP, A) JP-A-61-87117 (JP, A) JP-A-61-87118 (JP, A) JP-A-1-210914 (JP, A) JP-A-59-20018 (JP, A) JP-A-61-91613 (JP, A) JP-A-62-50718 (JP, A) JP-A-3-15911 (JP, A) JP-A-3-145614 (JP, A) JP-A-3-155513 (JP, A) JP-A-4-15612 (JP, A) A) Japanese Patent Publication No. 59-13003 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00- 25/04

Claims (5)

(57) [Claims] 1. A focus system comprising a front unit having a negative refractive power and a rear unit having a positive refractive power in order from the object side. In a zoom lens that changes a distance, the front lens unit has two or more aspheric surfaces in the front unit, and satisfies the following conditional expression. The zoom lens is characterized in that the aspherical surface of the front group satisfies all of the following conditional expressions: When the maximum effective diameter of the aspherical surface and y _max, 0 <y <0.8y
_For any height y in the vertical direction of the optical axis of _max , Here, φ ₁ : refractive power of the front group, φ ₂ : refractive power of the rear group, φ _W : refractive power of the entire system at the wide-angle end, N: refractive index of the aspherical object side medium, N ′: non- X (y): aspherical surface shape, X ₀ (y): aspherical reference spherical shape, where: r: reference radius of curvature of the aspheric surface, ε: quadratic surface parameter, A _i : aspheric surface coefficient,: paraxial radius of curvature of the aspheric surface ｛(1 /) = (1 / r) +2
A ₂ ｝, 2. A focal system of the whole system comprising a front group having a negative refractive power and a rear group having a positive refractive power in order from the object side, and by changing an air gap between the front group and the rear group. In a zoom lens that changes the distance, the rear group has two or more aspheric surfaces, and satisfies the following conditional expression; The zoom lens is characterized in that the aspherical surface of the rear group satisfies all of the following conditional expressions: When the maximum effective diameter of the aspherical surface and y _max, 0 <y <0.7y
_For any height y in the vertical direction of the optical axis of _max , Here, φ ₁ : refractive power of the front group, φ ₂ : refractive power of the rear group, φ _W : refractive power of the entire system at the wide-angle end, N: refractive index of the aspherical object side medium, N ′: non- X (y): aspherical surface shape, X ₀ (y): aspherical reference spherical shape, where: r: reference radius of curvature of the aspheric surface, ε: quadratic surface parameter, A _i : aspheric surface coefficient,: paraxial radius of curvature of the aspheric surface ｛(1 /) = (1 / r) +2
A ₂ ｝, 3. A focal system of the whole system comprising a front group having a negative refractive power and a rear group having a positive refractive power in order from the object side, and by changing an air gap between the front group and the rear group. In a zoom lens that changes the distance, the front group and the rear group each have at least one or more aspheric surfaces, and the entire system has two or more aspheric surfaces, and the rear group has two or three lenses. It is composed of two lenses and satisfies the following conditional expression, When the maximum effective diameter of the aspherical surface is y _max , 0 <y <0.8y
_For any height y in the vertical direction of the optical axis of _max , all the aspheric surfaces of the front group satisfy the following conditional expressions; When the maximum effective diameter of the aspherical surface is y _max , 0 <y <0.7y
a zoom lens characterized in that all the aspheric surfaces of the rear group satisfy the following conditional expression for an arbitrary height y in the vertical direction of the optical axis of _max : Here, φ ₁ : refractive power of the front group, φ ₂ : refractive power of the rear group, φ _W : refractive power of the entire system at the wide-angle end, N: refractive index of the aspherical object side medium, N ′: non- X (y): aspherical surface shape, X ₀ (y): aspherical reference spherical shape, where: r: reference radius of curvature of the aspheric surface, ε: quadratic surface parameter, A _i : aspheric surface coefficient,: paraxial radius of curvature of the aspheric surface ｛(1 /) = (1 / r) +2
A ₂ ｝, 4. The apparatus according to claim 1, wherein said front group comprises two lenses, and said rear group comprises three lenses.
4. The zoom lens according to any one of 3. 5. The zoom lens according to claim 1, wherein each of the front group and the rear group includes two lenses.