JPS60166912A - Photographic lens - Google Patents

Abstract

PURPOSE:To reduce the number of lens elements to be moved for focus adjustment by employing the five-group constitution of the 1st positive lens group, the 2nd negative lens group of cemented or separated positive and negative lenses, the 3rd negative meniscus lens group, the 4th positive lens group, and the 5th negative lens group. CONSTITUTION:The photographic lens system consists of the 1st lens group I which has positive refracting power, the 2nd lens group II of cemented or separated positive and negative lenses having negative refracting power, the 3rd lens group III of a negative meniscus lens, the 4th lens group IV of at least one positive lens, and the 5th lens group V of at least one negative lens having negative refracting power on the whole successively from the object side, and an equality holds. The focus adjustment is made by moving only the 3rd lens group III and the 4th lens group IV, and deterioration in aberrations resulting from the movement is corrected by the 5th lens group V to make the focus adjustment in an excellent aberration state from infinite distance to the closest distance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to biometa-type photographic lenses, and more particularly to their focusing.

In general, a hiometer type photographic lens consists of, in order from the object side, a first lens group consisting of a positive lens, a second lens group having negative refractive power consisting of a positive lens and a negative lens joined or separated, and a negative meniscus lens group. It has a third lens group consisting of a lens and a fourth lens group consisting of a positive lens.
4th Lensno! It is known as C, in which focus adjustment is performed by integrally moving the lens (2) in the direction of the optical axis. However, if you try to create a bright medium-telephoto lens with a focal length of about 80 to 100 wm and an F number of around 20 using a biometal type, the lens system will be quite large and its weight + i↓ will also be quite large. Therefore, the lens barrel will also be larger.

C1: In order to adjust the focus by moving such a lens system as a whole, the lens barrel becomes even larger and its structure becomes complicated, which is not preferable.

Furthermore, when adjusting focus using driving force such as a motor,
This is not preferable as it requires a large driving force.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks and to provide a photographic lens with good depiction performance while reducing the number of lenses that must be moved for focus adjustment.

In order to achieve the objective of L.
The second lens group (I
I), the third lens group consisting of a negative lens and a niscus lens (
III), a fourth lens group (IV) consisting of at least one positive lens, and a fifth lens group 141 (IV) consisting of at least one negative lens and having negative refractive power as a whole (V
> consists of the third lens group (+11) and the fourth lens group (
IV) is moved in the optical axis direction to perform focus adjustment, and is characterized in that it satisfies the following conditions.

However, here, Da is the axial air distance between the second lens group (II) and the third lens group ([1) in the infinity focused state, f III IV is the distance between the third lens group Qu) and the third lens group This is the combined focal length of the four lens groups.

The conventionally well-known biometa-type photographic lens consists of the first to fourth lenses (I) to σV) as described above, or
In the present invention, the fifth lens group (U+
) and the fourth lens group hood are moved to adjust the focus. Therefore, during focus adjustment, the third lens group (+>), the second lens group (11), and the fifth lens group (V) are fixed with respect to the image plane.
When performing focus adjustment by moving only the lens group (IV), the third lens group Qu) and the fourth lens I! YII
Since the composite refractive power with V) is positive, both lens groups (III) and (LV) must be extended toward the object side in order to perform closer-range Hefmaking. Therefore, in the infinity focus state, the third lens group θ■) or the second lens group (1■) and the diaphragm (S) placed immediately after it are extended to the nearest position without hitting them. 2nd lens group (11) and 3rd lens! ! The distance from T(tu) must be increased, which tends to increase the size of the lens system. However, in the present invention, by arranging the fifth lens group (V) having negative refractive power on the image side of the fourth lens group (tV), the positive refractive power of the fourth lens group (tV) can be increased. By increasing the strength, the combined refractive power of the third and fourth lenses (Ill, QV) can be strengthened, and the movement wind of both lens groups (III) (EV) can be reduced. Therefore, there is no need to significantly increase the distance between the second lens group (II) and the third lens mj (1n), and the compactness of the lens system can be maintained.

Furthermore, since the fifth lens group (V) cannot be moved during focus adjustment, the third lens group (V) cannot be moved for focus adjustment.
It is useful for correcting the sudden lack of correction of spherical aberration that occurs when the lens group Qn) and the fourth lens group (V) are moved toward the object side, and it also helps to correct the extroverted coma that occurs more strongly as it moves off-axis. It also helps correct aberrations.

According to the present invention, focus adjustment is performed by moving only the third lens group (Ill) and the fourth lens group (LV), so the movement quality is clearly smaller than that of the conventional example in which the entire lens is extended. . Therefore, focus adjustment is possible with a smaller driving force. Furthermore, as mentioned above, the third lens group (uQ
The aberration deterioration caused by the movement of the lens and the fourth lens group 1lv) is corrected by the fifth lens fil (V), and the focus is adjusted from infinity to the closest distance under good aberration conditions. can.

Is it okay to move the third lens group (III) and the fourth lens group (to) to a single plane or separately?Is it possible to move the third lens group (III) to a single plane or to move them separately?It is better to move the third lens group (III) to a single plane to simplify the configuration of the lens barrel. It comes.

When the lower limit of condition (1) is exceeded, lens 2 is moved for focus adjustment! Compared to the composite refractive power of T (11) (IV), the lens I! Since the air gap in front of -T(In) (v) becomes small, the lens group (III) (V) cannot be extended until a sufficiently short closest distance is obtained. Conversely, when the L limit of line 1't=(1) is exceeded, the second lens flT, (II
) and the third lens group (10) becomes large, which results in a lack of a peripheral light meter, and also increases aberration fluctuations during focus adjustment, making it difficult to correct them.

Further, in order to maintain a good aberration state, it is desirable that the following conditions are further satisfied.

(2) 4.0 < −(−+ −) f < 13.
0r7 rB Here, r7 is the radius of curvature of the object side surface of the third lens group @), rB is the radius of curvature of its image side surface, and f is the focal length of the entire system.

Line 1' (2) defines the radius of curvature of the object-side and image-side surfaces of the negative meniscus and threader constituting the third lens group (1). If the lower limit of condition (2) is exceeded, the third
The curvatures on both sides of the negative meniscus lenses that make up the lens group (lens group) become loose, so the third lens group @) and $
As the fourth lens group ([V)] moves forward, spherical aberration and field curvature are overcorrected, and coma aberration also increases. Conversely, if the upper limit of Article f'l: (2) is exceeded,
Since the curvatures of both sides of the negative meniscus lens are too steep, not only will spherical aberration be insufficiently corrected, but also the field properties will fluctuate greatly during focus adjustment.

The configuration of the embodiment of the present invention in the infinity focus state will be shown below. In each of the embodiments, focus adjustment is performed by integrally moving the third lens group ω1) and the fourth lens group (2).

(U margin) Example 1 [= 100 FNO = 2.55 2ω = 244° Radius of curvature Core thickness Refractive index, (Nd) 7・y 41 (νd
) r2259.76 and d2 0.20 T3 34.19 da 15.35 N2 1.60311 ν2 60
．． 74r473.11 d4. 3.43 d6 20.88 r9 109.71 dc+ 3.50 Ns 1.66608 νs 47
．． 95dll 1.70 N+5 1.54072 White 47.22ri2 500.00 2 Example 2 f=I00 F area=1.832ω=286° radius of curvature
Core thickness Refractive index (Nd) Atsube number (νd) Example 3 f-100FNO=2.55 2ω=244°Curvature V-
Diameter Core thickness Refractive index (Nd) Anobe number (νd) a −−0,336 ' Ill IV Example 4 f = 100 FNO = 1.83 2ω = 286° Radius of curvature Core thickness Refractive index Atsube number d43,44 d6 28.39 ds O, 20 dlOQ, 31 r12 300.00 T'IQ

[Brief explanation of the drawing]

1st. 4th. 7 and 10 are sectional views showing the lens configurations of Examples 1 to 4 of the present invention, 2nd, 5th and 10th embodiments, respectively. 8 and 11 are aberration curve diagrams in the infinity focus state of Examples 1 to 4, and 3. 6. FIGS. 9 and 12 are aberration curve diagrams when the lens systems of Examples 1 to 4 are focused at β=I/10. (Summer); 2nd lens group (Ill); 3rd lens group (+v); 4th lens group (V): 5th lens group (S); Aperture. Applicant: Minolta Camera Co., Ltd. Spherical aberration Sine condition Astigmatism Distortion %・Spherical aberration True imitation Astigmatism Distortion %l) A') Spherical aberration Sine condition Distortion % Spherical aberration Sine condition BUYU, Aberration Distortion % Spherical aberration Sine condition 11' point aberration Distortion % Procedural amendment document March 1980 1, Incident indication Patent application No. 23725 of 1982 2, Title of invention Photographic lens 3, Relationship with the case of the person making the amendment Applicant Address 2-80 Azuchi-cho, Higashi-ku, Osaka Osaka Kokusai Building name (607) Mino! Reta Camera Co., Ltd. voluntary amendment 5, subject of amendment (1) "Claims" column 6 of the specification Contents of the amendment (]) The full text of the "Claims" column of the specification is amended as shown in the attached sheet. (2) "Negative meniscus lens" in the third to second lines from the bottom of page 2 of the specification is corrected to "negative meniscus single lens." (3) "Negative meniscus lens" in the second line of page 4 of the specification is corrected to "negative meniscus single lens." Above attached amended claim 1: In order from the object side, a lens group having positive refractive power;
a second lens group consisting of a cemented or separated positive lens and a negative lens and having negative refractive power; a third lens group consisting of 11 negative meniscus lenses; a fourth lens group consisting of at least one positive lens; It consists of a fifth lens group consisting of at least one negative lens and having negative refractive power as a whole, and the focus is adjusted by moving the third lens group and 11 fourth lenses in the optical axis direction. , a photographic lens that satisfies the following conditions; where Da; axial air distance flllllV between the second and third lens groups in the infinity focus state; third lens group and the fourth lens group. 2. A photographic lens according to claim 1, which satisfies the following conditions; provided that 1'7; m 3 The radius of curvature of the object-side surface of the lens group 18; The radius of curvature of the image side surface of lens JI■ is the focal length of the entire system.

Claims (1)

[Claims] 1. Around 1 from the object side, there is a lens group having a positive refractive power, a second lens group having a negative refractive power consisting of a cemented or separated positive lens and a negative lens, and a negative meniscus. A third lens group consisting of a lens, a fourth lens group consisting of at least one positive lens, and a fifth lens group consisting of at least one negative lens and having a negative refractive power as a whole, and the third lens 11 and A photographic lens characterized in that C focus adjustment is performed by moving the fourth lens group in the optical axis direction and satisfies the following conditions; The second lens group and the third lens i in the infinity focus state! The axial air distance between f and fllllV; is the composite focal length of the third lens group and the fourth lens group. 2. A photographic lens according to claim 1, characterized in that it satisfies the following conditions; provided that: r7; radius of curvature r8 of the object-side surface of the third lens group;
The radius of curvature of the image-side surface of the lens group [; is the focal length of the entire system.