JP3033148B2 - 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 costs by reducing the number of lenses, see, for example, JP-A-54-78150 and JP-A-55-62420.
No., JP-B-60-46688, JP-A-1-210914, 1-2
No. 43011. These zoom lenses achieve a two-component zoom consisting of a negative front group (the front group is composed of two lenses) and a positive rear group.

Problems to be Solved by the Invention However, in these zoom lenses, since various aberrations caused by increasing the refractive power of each group cannot be corrected in a well-balanced manner, downsizing while maintaining performance has been achieved. Not really.

Therefore, an object of the present invention is to provide a low-cost, compact zoom lens with a small number of lenses while maintaining high optical performance.

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. The lens is characterized in that the front group is composed of two lenses, in order from the object side, a negative lens and a positive meniscus lens convex on the image side.

The rear group can be composed of two lenses, for example, a positive lens and a negative lens.

As mentioned above, to achieve compactness,
Although it is necessary to increase the refracting power of each lens, various aberrations worsen accordingly. According to the present invention, by configuring the front group as described above, it is possible to correct the various aberrations that have deteriorated in a well-balanced manner.

Here, a case where the front group is composed of two positive and negative lenses will be described. In this configuration, positive and negative refractive power arrangements are sequentially performed from the object side as shown in FIG. 9, and negative and positive refractive power arrangements are sequentially performed from the object side as shown in FIG. And the case of the refractive power arrangement of the front group of the present invention).

In the former case, as is clear from the optical path shown in FIG. 9, for the off-axis light, the light passing through the positive lens enters the negative lens at an incident angle larger than the incident angle to the positive lens. This is clearly disadvantageous in aberration correction. Further, since the negative power is increased due to the lower incident height of the negative lens, it becomes more difficult to correct aberration.

On the other hand, in the latter case, as shown in FIG. 10, light passing through the negative lens is incident on the positive lens at an angle of incidence smaller than the angle of incidence on the negative lens. It is advantageous. Further, since the incident power of the positive lens is increased, the positive power can be weakened, so that the aberration correction is facilitated.

Therefore, according to the configuration of the front group of the present invention, aberration correction can be easily and advantageously performed.

Also, by using a positive meniscus lens convex on the image side as the positive lens in the front group, aberration correction can be performed in a well-balanced manner.

In particular, it is preferable that the positive meniscus lens convex on the image side in the front group satisfies the following conditional expression.

Here, r _F : radius of curvature of the object side surface of the positive meniscus lens convex to the image side in the front group r _B : radius of curvature of the image side surface of the positive meniscus lens convex to the image side in the front group The above conditional expression defines the positive lens as a meniscus lens convex on the image side, and also defines a desirable shape thereof.

If the lower limit of the conditional expression is exceeded, the positive refractive power becomes relatively weak, making it difficult to correct lateral chromatic aberration. When the value exceeds the upper limit of the conditional expression, the positive refractive power becomes relatively strong, and the spherical aberration is insufficiently corrected.

As described above, by making the positive lens in the front group a meniscus lens convex to the image side, there is an effect on aberration correction, and also an effect on compactness as described below.

In the zoom lens according to the present invention, the distance between the front group and the rear group is minimized at the telephoto end. It is desirable to make this interval as short as possible for compactness. On the other hand, when considering the position where off-axis light intersects the optical axis, a stop may need to be provided between the front group and the rear group. In such a case, it is necessary to secure a space for arranging the aperture between the front and rear groups even at the telephoto end, so it is difficult to shorten the interval between the front and rear groups.

However, if the positive lens in the front group is a meniscus lens convex to the image side, it is difficult to hit when the lens approaches the stop, so that the distance between the positive lens on the front group image side and the positive lens on the rear group object side is short. However, a sufficient space for arranging the aperture can be secured. Therefore, the overall length of the zoom lens can be shortened, and the zoom lens can be made compact.

As described above, according to the configuration of the present invention, a high-performance and compact zoom lens can be realized.
By satisfying the following conditional expressions ~,
It is possible to perform better aberration correction.

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

Here, φ _W : refractive power of the whole system at the wide-angle end φ _T : refractive power of the whole system at the telephoto end β: zoom ratio φ ₁ : refractive power of the front group φ ₂ : refractive power of the rear group where φ ₁ < it is _{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.

Satisfying the following conditional expressions is also effective for maintaining a good balance between the entire length of the lens, the amount of movement for zooming, the back focus, and the state of correction of various aberrations.

However, φ ₁ <0.

The conditional expression defines the ratio between the refractive power of the entire system and the refractive power of the front group at the wide-angle end. 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.

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.

If an aspherical surface is used for the positive lens in the front group, more favorable aberration correction can be performed.

It is desirable that the object-side surface of the positive lens in the front group be an aspheric surface that satisfies the following conditional expression.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
0.3Y _max <y <Y _{max For} any optical axis vertical direction y, Here, N: the refractive index of the aspherical object-side medium N ′: the refractive index of the aspherical image-side medium X (y): the aspherical surface shape X ₀ (y): the aspherical reference spherical shape r: Reference radius of curvature of aspheric surface ε: Quadratic surface parameter A _i : Aspheric surface coefficient It is.

If the lower limit of the conditional expression is exceeded, the diverging effect at the periphery becomes weak, so that the incident angle of the peripheral light beam to the rear group becomes large, and it becomes difficult to correct coma. If the upper limit is exceeded, the diverging effect becomes too strong, and it becomes difficult to correct curvature of field and distortion.

It is desirable that the image-side surface of the positive lens in the front group be an aspheric surface that satisfies the following conditional expression.

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

If the lower limit of the conditional expression is exceeded, the convergence effect will be too strong, and the spherical aberration will fall too far to the underside in combination with the strong positive refractive power of the rear group. If the upper limit is exceeded, coma and spherical aberrations are advantageous, but it becomes difficult to correct distortion.

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 optical axis vertical direction y of 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 ,
0.7Y _max <y <Y _{max For} any optical axis vertical direction y, It is.

The conditional expression is, when the maximum effective diameter of the aspheric surface is Y _max ,
0.7Y _max <y <Y _{max For} any optical axis vertical direction y, 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.

Desirably, the deviation amount of the aspheric surface on the side satisfying the conditional expression from the reference spherical surface is larger than the deviation amount of the aspheric surface on the side satisfying the conditional expression from the reference spherical surface.

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 _i (i = 1, 2, 3,...) Is the radius of curvature of the i-th surface counted from the object side, d _i (i = 1, 2,
3, ...) indicates the i-th axial top surface distance counted from the object side, and N _i (i = 1,2,3, ...), ν _i (i = 1,2,3, ..). .) Is the refractive index for the d-line of the i-th lens counted from the object side,
Indicates Abbe number. 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> f = 36.0~49.5~68.0 F NO =} 4.6~5.2~5.65 Aspheric coefficient r ₁ : ε = 0.10000 x 10 A ₄ = 0.48761 x 10 ^-4 A ₆ = -0.15305 x 10 ^-6 A ₈ = 0.45908 x 10 ^-8 A ₁₀ =-0.34 295 x 10 ^-10 A ₁₂ = 0.21624 x 10 ^-12 r ₃ : ε = 0.10000 × 10 A ₄ = −0.17569 × 10 ⁻³ A ₆ = −0.59719 × 10 ⁻⁶ A ₈ = −0.79896 × 10 ⁻⁸ A ₁₀ = −0.96881 × 10 ⁻¹⁰ A ₁₂ = −0.53336 × 10 ⁻¹² r ₄ : ε = 0.10000 × 10 A ₄ = −0.12910 × 10 ⁻³ A ₆ = −0.13775 × 10 ⁻⁶ A ₈ = −0.58539 × 10 ⁻⁸ A ₁₀ = 0.10359 × 10 ⁻¹⁰ A ₁₂ = 0.10473 x 10 ^-12 r ₅ : ε = 0.10000 x 10 A ₄ = -0.15664 x 10 ^-4 A ₆ = 0.10003 x 10 ^-6 A ₈ = -0.33605 x 10 ^-8 A ₁₀ = 0.29786 x 10 ^-10 A ₁₂ = -0.83124 x 10 ^-13 r ₇ : ε = 0.10000 x 10 A ₄ = 0.44362 x 10 ^-4 A ₆ =-0.13619 x 10 ^-6 A ₈ = 0.69744 x 10 ^-9 A ₁₀ = 0.36316 x 10 ^-11 A ₁₂ = -0.25001 × 10 ^-13 r ₈ : ε = 0.10000 × 10 A ₄ = 0.11504 × 10 ^-3 A ₆ = 0.24271 × 10 ^-6 A ₈ = 0.25414 × 10 ^-8 A ₁₀ = -0.81397 × 10 ^-13 A ₁₂ = -0.10403 × 10 ^-12 <example _{2> f = 36.0~49.5~68.0 F NO =} 4.6~5.2~5.65 Aspheric coefficient r ₁ : ε = 0.10000 x 10 A ₄ = 0.32261 x 10 ^-4 A ₆ = -0.17384 x 10 ^-6 A ₈ = 0.34093 x 10 ^-8 A ₁₀ =-0.25439 x 10 ^-10 A ₁₂ = 0.95957 x 10 ^-13 r ₃ : ε = 0.10000 x 10 A ₄ = -0.11918 x 10 ^-3 A ₆ = -0.30837 x 10 ^-6 A ₈ = -0.36 626 x 10 ^-8 A ₁₀ = -0.32097 x 10 ^-10 A ₁₂ = −0.15496 × 10 ⁻¹³ r ₄ : ε = 0.10000 × 10 A ₄ = −0.92420 × 10 ⁻⁴ A ₆ = −0.63550 × 10 ⁻⁷ A ₈ = −0.31442 × 10 ⁻⁸ A ₁₀ = −0.28788 × 10 ⁻¹¹ A ₁₂ = 0.14181 × 10 ^-12 r ₅ : ε = 0.10000 × 10 A ₄ = -0.20468 × 10 ^-4 A ₆ = 0.31399 × 10 ^-7 A ₈ = -0.22270 × 10 ^-8 A ₁₀ = 0.90776 × 10 ^-11 A ₁₂ = -0.35883 x 10 ^-13 r ₆ : e = 0.10000 x 10 A ₄ =-0.21932 x 10 ^-4 A ₆ =-0.72202 x 10 ^-7 A ₈ = 0.54981 x 10 ^-10 A ₁₀ =-0.11269 x 10 ^{_{-10 A 12 = 0.48293 × 10 -13}} r 8: ε = 0.10000 × 10 A 4 = 0.54424 × 10 -4 A 6 = 0.17441 × 10 -6 A 8 = 0.35623 × 10 -9 A 10 = -0.84395 × 10 - ^{_{12 A 12 = 0.38732 × 10 -13}} < example _{3> f = 36.0~49.5~68.0 F NO =} 4.6~5.2~5.65 Aspheric coefficient r ₁ : ε = 0.10000 × 10 A ₄ = 0.23996 × 10 ^-4 A ₆ = -0.11664 × 10 ^-6 A ₈ = 0.37841 × 10 ^-8 A ₁₀ =-0.35590 × 10 ^-10 A ₁₂ = 0.16451 × 10 ^-12 r ₃ : ε = 0.10000 x 10 A ₄ = -0.11749 x 10 ^-3 A ₆ = -0.39275 x 10 ^-6 A ₈ = -0.42481 x 10 ^-8 A ₁₀ = -0.35131 x 10 ^-10 A ₁₂ = 0.29834 × 10 ^-14 r ₄ : ε = 0.100 × 10 A ₄ = −0.91674 × 10 ⁻⁴ A ₆ = −0.52 135 × 10 ⁻⁷ A ₈ = −0.37133 × 10 ⁻⁸ A ₁₀ = −0.24487 × 10 ⁻¹² A ₁₂ = 0.15003 x 10 ^-12 r ₅ : ε = 0.10000 x 10 A ₄ = -0.25231 x 10 ^-5 A ₆ = 0.24205 x 10 ^-6 A ₈ = -0.20384 x 10 ^-8 A ₁₀ = 0.11086 x 10 ^-10 A ₁₂ = 0.21595 x 10 ^-13 r ₆ : ε = 0.10000 x 10 A ₄ = 0.55329 x 10 ^-5 A ₆ = 0.22957 x 10 ^-6 A ₈ = -0.13147 x 10 ^-8 A ₁₀ = -0.23746 x 10 ^-10 A ^{_{12 = 0.17962 × 10 -12 r 7}} : ε = 0.10000 × 10 A 4 = -0.88146 × 10 -4 A 6 = -0.41099 × 10 -6 A 8 = -0.40488 × 10 -8 A 10 = -0.47904 × 10 - ¹⁰ A ₁₂ = −0.52478 × 10 ⁻¹² <Example 4> f = 36.0 to 49.5 to 68.0 F _NO = 4.6 to 5.2 to 5.65 Aspheric coefficient r ₁ : ε = 0.10000 x 10 A ₄ = 0.17891 x 10 ^-4 A ₆ = -0.11037 x 10 ^-6 A ₈ = 0.38097 x 10 ^-8 A ₁₀ = -0.33295 x 10 ^-10 A ₁₂ = 0.18005 x 10 ^-12 r ₃ : ε = 0.10000 x 10 A ₄ = -0.11502 x 10 ^-3 A ₆ = -0.46524 x 10 ^-6 A ₈ = -0.49570 x 10 ^-8 A ₁₀ = -0.75549 x 10 ^-10 A ₁₂ = −0.57006 × 10 ⁻¹² r ₄ : ε = 0.10 × 10 × 10 A ₄ = −0.90313 × 10 ⁻⁴ A ₆ = −0.15729 × 10 ⁻⁶ A ₈ = −0.42148 × 10 ⁻⁸ A ₁₀ = 0.17514 × 10 ⁻¹¹ A ₁₂ = -0.62 122 x 10 ^-13 r ₇ : e = 0.10000 x 10 A ₄ = 0.32 240 x 10 ^-4 A ₆ = 0.24784 x 10 ^-6 A ₈ = -0.87517 x 10 ^-9 A ₁₀ = 0.11275 x 10 ^-11 A ₁₂ = 0.47 100 x 10 ^-14 r ₈ : ε = 0.10000 x 10 A ₄ = 0.60991 x 10 ^-4 A ₆ = 0.23001 x 10 ^-6 A ₈ = 0.14152 x 10 ^-8 A ₁₀ = -0.19258 x 10 ^-11 A ₁₂ = 0.74110 × 10 ^-14 Figure 1 - Figure 4 is a lens configuration diagram corresponding to the examples 1 to 4, from the most wide-angle end of the arrow is the front group and the rear group in the drawing (S) top The movement toward the telephoto end (L) is schematically shown.

The first embodiment includes, in order from the object side, a front lens group including a negative meniscus lens concave to the image side and a second lens including a positive meniscus lens convex to the image side, and a biconvex positive third lens. And a rear group consisting of a fourth lens made of a negative meniscus concave on the image side. Example 1
At the object-side surface of the first lens, both surfaces of the second lens,
The object-side surface of the third lens and both surfaces of the fourth lens are aspherical.

The second embodiment includes, in order from the object side, a front lens unit including a first lens including a biconcave negative lens and a second lens including a positive meniscus lens convex on the image side, and a biconvex positive third lens and a double lens. And a rear group consisting of a fourth lens consisting of a concave negative lens. In Example 2, the object-side surface of the first lens, both surfaces of the second lens, both surfaces of the third lens, and the image-side surface of the fourth lens are aspherical.

In the third embodiment, in order from the object side, a front group consisting 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, and a positive meniscus lens convex on the object side And a rear group consisting of a fourth lens consisting of a biconcave negative lens. In Example 3, the object-side surface of the first lens, both surfaces of the second lens, both surfaces of the third lens, and the object-side surface of the fourth lens are aspherical.

In the fourth 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 4, the object-side surface of the first lens, both surfaces of the second lens, and both surfaces of the fourth lens are aspherical.

5 to 8 are aberration diagrams corresponding to Examples 1 to 4, 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 broken line (SC) represents the sine condition. Further, a broken line (DM) and a solid line (DS) represent astigmatism on the meridional surface and the sagittal surface, respectively.

Table 1 shows the conditional expressions in Examples 1 to 4. In the conditional expression Are shown respectively.

Table 2 shows that in the conditional expressions in Examples 1 to 4, In the conditional expression And in the conditional expression Are shown respectively.

Tables 3 to 6 correspond to Examples 1 to 4, 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, and FIG. 4 are lens configuration diagrams corresponding to Examples 1 to 4 of the present invention, respectively. FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are aberration diagrams corresponding to Examples 1 to 4 of the present invention, respectively. 9 and 10 are diagrams for explaining the refractive power arrangement of the front group constituting the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-78150 (JP, A) JP-A-1-210914 (JP, A) JP-A-1-243011 (JP, A) JP-A-3- 261906 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (1)

(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 the zoom lens for changing the distance, the front unit is composed of two lenses, a negative lens made of a homogeneous medium and a positive meniscus lens convex on the image side, in order from the object side, and A zoom lens characterized by satisfying the formula; Here, r _{F is the} radius of curvature of the object-side surface of the positive meniscus lens, and r _{B is the} radius of curvature of the image-side surface of the positive meniscus lens.