JPH0820600B2 - Zoom lens - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a zoom lens including a wide angle of view whose maximum angle of view exceeds 60 ° and having a wide zoom range from a so-called wide angle to a telephoto position.

[Conventional technology]

In recent years, in this type of zoom lens, various ones for a 35 mm size steel camera have been proposed. In order from the object side, the first lens group having positive refracting power, the second lens group having negative refracting power, and the second lens group having positive refracting power A four-group type zoom lens composed of a third lens group and a fourth lens group having a positive refractive power is mainly used. In the zoom lens having such a configuration, the first
The lens group, the second lens group, and the third lens group often form an afocal system in most cases, and the fourth lens group mainly has an image forming action.

As the fourth lens group of this four-group zoom lens,
Conventionally, two types of configurations have been proposed. The first is
As disclosed in JP-A-57-169716 and JP-A-60-59315, the power distribution is positive, negative, positive, and positive in order from the object side. And the second is a configuration comprising negative, positive, and positive power distribution in order from the object side, as disclosed in Japanese Patent Application Laid-Open No. 58-78114 by the same applicant as the present application.

[Problems to be solved by the invention]

In the former case, since the positive and negative values are sequentially provided from the object side, the object side principal point of the fourth lens group can be moved to the object side, but in reality, the positive and negative combined refraction on the object side is achieved. Since the force is negative, the object-side principal point of the fourth lens group cannot be moved to the object side very much. Therefore, in order to secure an air gap between the third lens group and the fourth lens group, it is necessary to maintain a large principal point gap between the third lens group and the fourth lens group, and the entire optical system becomes long. . In addition, the distance between the lenses that carry the positive and negative powers on the object side is also large, which is also disadvantageous for making the fourth lens group compact.

Further, in the latter case, the lens structure that bears the negative power on the object side is actually a structure in which a positive lens and a negative lens are cemented or slightly separated, and the fourth lens group is compact compared to the former case. However, since the negative power is distributed to the object side, the object-side principal point position of the fourth lens group is unlikely to move to the object side. Therefore, as in the former case, it is necessary to maintain a large principal point distance between the third lens group and the fourth lens group in order to secure an air distance between the third lens group and the fourth lens group. , The whole optical system becomes long.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to solve the above-mentioned problems and to provide a zoom lens which has a simple structure and has a short total lens length and which maintains excellent imaging performance over a wide zoom range from wide angle to telephoto. I am trying.

[Means for solving problems]

The present invention relates to a first lens group having positive refracting power in order from the object side.
G ₁ , a second lens group G _{2 having} a negative refractive power, a third lens group G _{3 having a} positive refractive power, and a fourth lens group G ₄ having a positive refractive power, and the first lens group G ₁ and the third lens It is based on a zoom lens that performs zooming from the wide-angle end to the telephoto end by moving the group G ₃ and the fourth lens group G ₄ to the object side. The fourth lens group G ₄ has a positive meniscus lens L ₁₀ having a weak positive refractive power with a convex surface facing the object side, the positive meniscus lens has a refractive power of φ ₁₀ (diopter), and a refractive index of n. , And the center thickness is d, and the radiuses of curvature of the object-side and image-side lens surfaces are Ra and Rb, respectively, 10> (Rb−Ra) φ ₁₀ > −dφ ₁₀ (n−1) / n (1 ) Is satisfied.

[Work]

According to the configuration of the fourth lens group G _4, since the negative power on the object side of the fourth lens group G ₄ does not exist, the object side principal point of the fourth lens group G ₄ prior the It is possible to shift to the object side compared to the case of the configuration. Therefore,
The third lens group G ₃ and the third lens group G ₃ it is possible to reduce the principal point distance between the fourth lens group G ₄ fourth lens group G ₄
Since it is possible to secure a sufficient air space between them, the overall length of the optical system can be reduced, and the shape of the lens system can be made compact. Further, by setting the positive meniscus lens L ₁₀ in the fourth lens group G ₄ within the range of the above conditions, the fluctuations of astigmatism and spherical aberration due to zooming are well balanced, and stable imaging performance is maintained. It becomes possible to do.

That is, from the value of the third-order aberration coefficient, the fourth lens group G ₄
In the positive meniscus lens L ₁₀ with the convex surface facing the object side, the value of the astigmatism coefficient III is slightly positive at the wide-angle end, changes slightly to negative at the telephoto end, and falls within a small absolute value range. It suppresses fluctuations. The value of the spherical aberration coefficient I has a certain positive value at the wide-angle end, and has a considerably large positive value at the telephoto end. Due to such aberration balance, the entire system in the entire zoom range is A stable aberration correction state of is realized.

To describe formula (1) above in detail, in a thick lens such as the positive meniscus lens L ₁₀ in the fourth lens group G ₄ , its refractive power φ ₁₀ is Is given. Here, n is the positive meniscus lens L ₁₀
, D is the center thickness.

From this relational expression, in order for this lens to have positive refractive power, It is necessary to satisfy the condition of.

On the other hand, regarding the shape and refractive power of the positive meniscus lens L ₁₀ , it is necessary to satisfy the condition of (Rb−Ra) φ ₁₀ <10 (3) from the viewpoint of aberration correction. Here, φ ₁₀ is a value that represents the refractive power of the positive meniscus lens in diopter units. If this condition is not satisfied, the refractive power of the positive meniscus lens becomes too strong, and spherical aberration and astigmatism have large values in the negative direction, making it difficult to correct them by other components.

Therefore, it is necessary for the positive meniscus lens L ₁₀ in the fourth lens group G ₄ to satisfy the condition of the above expression (1).

Further, in the present invention, the fourth lens group G ₄ has the positive meniscus lens L ₁₀ as described above as the most object-side component,
Following this, a positive lens with a stronger curvature facing the image side
L _11, it is desirable to be composed of a cemented positive lens L ₁₂ consisting of lamination of a biconvex positive lens and a negative lens, cemented surface of the cemented positive lens L ₁₂ is be configured to have a diverging action preferable. And specifically, this cemented lens L
_{If the} refractive power of the ₁₂ bonding surfaces is φs and the combined refractive power of the fourth lens group G ₄ is φ ₄ , it is desirable that the condition of −1.5 <φs / φ ₄ <−0.5 (4) be satisfied. .

When the refractive power of the cemented surface of the cemented lens L ₁₂ of the positive refractive power located closest to the image side in the fourth lens group G ₄ exceeds the upper limit described above, spherical aberration and astigmatism on the wide angle side are negative. However, it becomes difficult to correct aberrations. On the other hand, when the value goes below the lower limit, spherical aberration on the telephoto side becomes large in the positive direction, and if an attempt is made to correct this, the balance of astigmatism at the wide-angle end and the telephoto end deteriorates. In addition, this condition is also important for achieving downsizing of the fourth lens group G ₄ , and hence downsizing of the entire system, while maintaining good aberration balance. That is, if the upper limit of this condition is exceeded, the tele ratio of the fourth lens group G ₄ (the ratio of the distance from the apex of the frontmost lens surface of the lens to the image surface with respect to the focal length) becomes large, and the lens system becomes large. On the other hand, if the lower limit of this condition is not satisfied, the Tell ratio becomes small, which is advantageous for downsizing, but it becomes difficult to correct aberration.

Further, as a specific configuration of the third lens group G ₃ in the present invention, a biconvex positive lens L ₇ having a surface having a stronger curvature toward the image side and a negative meniscus lens having a convex surface facing toward the image side are sequentially arranged from the object side. It is desirable that it is composed of L ₈ and a positive meniscus lens L ₉ having a convex surface facing the object side. And these third
When the shape factors of the three components in the lens group G ₃ are q ₇ , q ₈ , and q ₉ , respectively, −1.0 <q ₇ <−0.3 (5) 2.0 <q ₈ <5.0 (6) 2.5 It is desirable that the conditions <q ₉ <5.0 (7) are satisfied in order to satisfactorily correct spherical aberration, coma and astigmatism over the entire zoom range.

The shape factor q is defined as q = (R ₂ + R ₁ ) / (R ₂ −R ₁ ), where R ₁ and R ₂ are the radii of curvature of the object-side and image-side lens surfaces of each lens. Shall be done.

〔Example〕

Each of the examples according to the present invention is a zoom lens for a 35 mm single-lens reflex camera, and has a focal length f = 35 mm to 13 mm.
It has 5 mm and an F number of about 3.5 to 4.5.

This zoom lens has a lens configuration diagram of FIG.
As shown in the schematic diagram of the lens group movement locus in the figure, in order to perform zooming from the wide-angle end to the telephoto end, the first lens group G ₁ , the third lens group G ₃ , and the fourth lens group G ₄ are respectively placed on the image plane. On the other hand, the second lens group G ₂ moves toward the object side, moves toward the object side near the wide-angle end, and then moves non-linearly toward the image plane side. It is the same as the present invention that the second lens group G ₂ having negative refractive power moves toward the object side in the vicinity of the wide-angle end, so that the effective diameter of the first lens group G ₁ can be suppressed to a small size and the lens system can be made compact. This is as disclosed in the above-mentioned JP-A-58-78114 by the applicant.

Further, the first lens group G ₁ and the fourth lens group G ₄ are integrally linked and moved, and the second lens group G ₂ and the third lens group G ₃
There are times when moves nonlinearly with respect to the first lens group G _1, the synthesis system from the first lens group G ₁ during the movement for zooming to the third lens group G ₃ to form the afocal system At this time, the space between the third lens group G ₃ and the fourth lens group G ₄ forms a parallel light beam system. Here, the second lens group G ₂ has a substantial image plane correction function, and by changing the interval (afocal portion) between the third lens group G ₃ and the fourth lens group G ₄ which are parallel light fluxes. It is as disclosed in Japanese Patent Application Laid-Open No. 61-123811 filed by the same applicant as the present application that the variation of aberration due to zooming can be corrected.

In FIG. ₂ , the broken line drawn along the movement locus of the second lens group G ₂ indicates the second movement in order to facilitate understanding of the movement.
A state where the lens group G ₂ is fixed at the wide-angle end position is shown, and a broken line along the movement locus of the third lens group G ₃ indicates
Similarly, in order to make it easier to understand the movement state, the case where the positions of the wide-angle end and the telephoto end of the third lens group G ₃ are linearly moved is shown.

As shown in the sectional view of FIG. 1, the first lens group G ₁ having a positive refracting power has a negative meniscus lens L ₁ having a convex surface directed toward the object side at the most object side. The second lens group G ₂ having a negative refractive power is composed of a convex positive lens L ₂ and a positive lens L ₃ arranged closest to the image side and having a convex surface directed toward the object side. It is composed of a negative meniscus lens L ₄ directed toward the negative lens, a negative lens L ₅ bonded together, and a negative lens L ₆ bonded toward the surface having a stronger curvature toward the object side. The third lens group G ₃ having a positive refractive power includes, in order from the object side, a biconvex positive lens L _{7 with} a surface having a stronger curvature facing the image side, a negative meniscus lens L ₈ having a convex surface facing the image side, and the object side. the convex surface and a positive meniscus lens L _9, which toward the fourth lens group G ₄ having a positive refractive power in order from the object side, a meniscus lens L ₁₀ of weak positive refractive power with a convex surface facing the object side, a strong image side It is composed of a positive lens L ₁₁ having a surface of curvature and a cemented positive lens L ₁₂ formed by cementing a biconvex positive lens and a negative lens having a surface of stronger curvature to the object side. An iris diaphragm S is arranged between the second lens group G ₂ and the third lens group G ₃ and is configured to move along the optical axis integrally with the third lens group G ₃ . .

The following Tables 1 and 2 show the first and second embodiments of the present invention.
The specifications of the embodiment are shown. In the table, the numbers at the left end indicate the order from the object side, and the refractive index and Abbe number are d-line (λ = 587.6n
This is the value for m).

The aberration correction function of the meniscus lens L _{10 having} a weak positive refracting power directed to the object side in the fourth lens group G _{4 which} is a feature of the present invention will be examined with reference to the aberration coefficient of each of the above-described examples. .

The values of the third-order aberration coefficients on the object-side and image-side surfaces of this positive meniscus lens L ₁₀ tend to cancel out because their signs are opposite to each other, but the sum of the third-order aberration coefficients of astigmatism on both surfaces is and III _10, when representing the sum of third-order aberration coefficient of the spherical aberration and I _10, in the state of the wide-angle end and the telephoto end, has a value shown in Table 3 below.

As shown in Table 3 above, in the meniscus lens L ₁₀ in the fourth lens group G ₄ , the third-order aberration coefficient of astigmatism is about the same as the combined amount of the entire system at the telephoto end, and It can be seen that the combined amount and the absolute value are the same, but the signs are opposite, and the aberrations are distributed according to the magnification change.
Regarding the third-order aberration coefficient of spherical aberration, it has a value that is similar to the combined amount of the entire system at the wide-angle end, and at the telephoto end, the combined amount of the entire system is slightly negative, but a fairly large positive value. It can be seen that good correction is made according to the balance with other components.

Aberration diagrams for the first and second examples are shown in FIGS. 2 and 3, respectively. In each aberration diagram,
Spherical aberration, astigmatism, and distortion are wide-angle end, middle (f = 8
5.0), in each state at the telephoto end.

From these various aberration diagrams, while the zoom lens according to the present invention has a wide zoom range and a compact configuration,
It can be seen that various aberrations are well corrected.

[Effect]

According to the above, as the present invention, has a high variable magnification ratio of the zoom ratio 3.8 at about F-number 3.5 contains the maximum field angle is Hiromichi angle of 60 ° or more, the total length the fourth lens group G ₄ with a simple structure A zoom lens having excellent imaging performance over the entire zoom range can be achieved even though the zoom lens is very short.

[Brief description of drawings]

FIG. 1 is a sectional view showing a lens configuration of a zoom lens according to the present invention, FIG. 2 is a schematic view showing a movement locus of a lens group, FIG. 3 is a diagram showing various aberrations of the first embodiment according to the present invention, and FIG. [Fig. 8] is a set of aberration diagrams for the second example according to the present invention. [Explanation of Signs of Main Parts] G ₁ ...... First lens group G _{2 with} positive refracting power G ₂ …… Second lens group G _{3 with} negative refracting power G ₃ …… Third lens group G _{4 with} positive refracting power G ₄ …… Positive refraction Fourth lens group of power

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-270910 (JP, A) JP 61-90120 (JP, A) JP 61-87121 (JP, A) JP 61- 62012 (JP, A) JP 60-221717 (JP, A) JP 60-26312 (JP, A) JP 60-14214 (JP, A) JP 60-14213 (JP, A)

Claims (3)

[Claims] 1. A first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a positive refracting power, which are arranged in this order from the object side. In a zoom lens that performs zooming from the wide-angle end to the telephoto end by moving the first lens unit, the third lens unit, and the fourth lens unit to the object side, the fourth lens unit has a convex surface facing the object side. Has a positive meniscus lens component, the refractive power of the positive meniscus lens component is φ ₁₀ (diopter), the refractive index is n, the center thickness is d, and the radius of curvature of the object-side and image-side lens surfaces of the positive meniscus lens component , respectively, when Ra, and Rb is, 10> (Rb-Ra) φ 10> -dφ 10 (n-1) / n zoom lens satisfies the condition. 2. The fourth lens group includes a positive lens component having a surface having a stronger curvature toward the image side of the positive meniscus lens component, and a biconvex positive lens and a surface having a stronger curvature toward the object side. had a positive cemented lens component consisting of the junction of the negative lens, when the refractive power having a cemented surface of the cemented positive lens component .phi.s, and the composite refractive power of the fourth lens group phi _4, - Claim 1 characterized in that the condition of 1.5 <φs / φ ₄ <−0.5 is satisfied.
The zoom lens described in the item. 3. The third lens group comprises, in order from the object side, a biconvex positive lens component having a surface having a stronger curvature toward the image side, a negative meniscus lens component having a convex surface toward the image side, and a convex surface toward the object side. When the shape factor of the three components is q ₇ , q ₈ , and q ₉ , respectively, -1.0 <q ₇ <-0.3 2.0 <q ₈ <5.0 2.5 <q ₉ <5.0 The zoom lens according to claim 2, wherein each of the conditions is satisfied. However, the shape factor q is defined by q = (R ₂ + R ₁ ) / (R ₂ −R ₁ ), where R ₁ and R ₂ are the radii of curvature of the object-side and image-side lens surfaces of the lens, respectively. Shall be done.