JPH03249719A - Compact photographic lens - Google Patents

Abstract

PURPOSE:To obtain the compact, high-performance photographic lens suitable for a lens shutter camera by dividing a lens system into a front and a rear group across a stop and giving the front group positive refracting power and the rear group negative refracting power, and varying the refracting power of the rear group from positive to negative in order from the object side and using a negative lens as the lens closest to the image side. CONSTITUTION:The lens consists of two groups, i.e. the front group with the positive refracting power and the rear group with the negative refracting power across the stop S in order from the object side. The front group consists of a 1st positive meniscus lens I which has a convex surface on the object side, a 2nd negative lens II, and a 3rd biconvex lens III in order from the object side and the rear group consists of a 4th positive meniscus lens IV which is convex to the image side and a 5th negative meniscus lens V which is convex to the image side in order from the object side. Consequently, the compact lens which has a large view angle and an about 1.1 telephoto ratio is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographic lens, and particularly relates to a compact and high-performance photographic lens for lens shutter cameras.

In the above lenses, in order to make the entire camera compact, it is desirable to shorten the overall length of the lens. To shorten the total length of the lens, add positive refractive power to the front of the lens thread.
It is known to employ a so-called telephoto type optical system in which a negative refractive power is arranged at the rear of the lens system. However, this type of optical system is generally used in telephoto lenses with a narrow angle of view, and when used in wide-angle lenses with a wide angle of view, it is extremely difficult to satisfactorily correct various aberrations over the entire screen.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above problems and provide a compact, high-performance photographic lens suitable for lens-shutter cameras.

A further object of the present invention is to provide a photo lens that allows for a wide-angle lens while also making the entire camera more compact and simple.

In order to achieve the above object, the photographic lens of the present invention consists of two groups in order from the object side across the aperture: a front group with positive refractive power and a rear group with negative refractive power. The group consists of, in order from the object side, a first lens that is a positive meniscus lens with its convex surface facing the object side, a second lens that is a single member lens, and a third lens that is a biconvex lens, and the rear group includes, in order from the object side,
It is characterized by a five-lens configuration, consisting of a fourth lens that is a positive meniscus lens that is convex to the image side, and a fifth lens that is a negative meniscus lens that is convex to the image side.

In the present invention, in order to shorten the overall length of the lens, the lens is divided into two groups, the front group and the rear group, with an aperture in between, and the refractive power of each is made into a telephoto type, with the front group having positive refractive power and the rear group having negative refractive power. ing. However, in this case, if you try to make the lens more compact while ensuring sufficient back focus, you will have to increase the refractive power of the rear group, which will eventually worsen aberrations, especially if distortion is positive. There is a marked tendency for the value to become large. In the present invention, the value of distortion at the periphery of the screen is reduced by configuring the rear group lenses to have positive and negative refractive powers in order from the object side. By making the lens closest to the image side a negative lens, the lens aperture is suppressed from increasing, and lateral chromatic aberration at the periphery of the screen is also well corrected. Furthermore, by forming both lenses in the rear group into a meniscus shape that is convex toward the image edge, off-axis field curvature is effectively corrected.

By adopting such a lens configuration, a compact lens with a large angle of view (2ω=84°) and a telephoto ratio of about 1.1, which has been difficult to design in the past, can be achieved. Furthermore, it is desirable that the photographic lens of the present invention satisfy the following conditions.

4 0.05 < - < 0.50 (1) I: stock, f: focal length of the entire system, d: air distance between the front and rear groups.

Condition (1) stipulates the air gap between the front group and the rear group; if this upper limit is exceeded, it becomes difficult to make the overall length compact; if the lower limit is exceeded, the air gap between the front group and the rear group is If the gap becomes too small, it becomes difficult to insert the aperture, and the lens barrel configuration becomes complicated.

Furthermore, it is desirable that the photographic lens of the present invention satisfy the following conditions.

4 1.0 <−< 15.0 (2) However, f4: Focal length of the fourth lens, f7: Radius of curvature of the object side surface of the fourth lens, f,: Fourth lens
Radius of curvature of the image side surface of the lens.

Condition (2) defines the refractive power of the fourth lens; if this lower limit is exceeded, the refractive power of the fourth lens becomes too strong, so the refractive power of the fifth lens must also be made strong, which causes various aberrations. It becomes difficult to correct. Furthermore, if this upper limit is exceeded, it becomes impossible to suppress the positive increase in distortion at the periphery of the screen.

Condition (3) defines the shape of the fourth lens and relates to correction of field curvature.

If this upper limit is exceeded, the curvature of field becomes a large negative value, and the image surface tends to be under-tilted. In addition, inward coma is more likely to occur. When the lower limit is exceeded, the curvature of field becomes a large positive value, and the image plane falls to the over side, making it easier for extroverted coma to occur.

By the way, in the photographic lens of the present invention, if only the front group is moved integrally without moving the rear group during focusing, the amount of lens movement can be smaller than when both the front and rear groups are moved. Furthermore, since cameras with built-in photographic lenses like the one of the present invention are generally lens shutter cameras, focusing can be performed by moving only the front group without moving the aperture member, so the torque of the actuator to move the lens can be reduced. The lens barrel configuration can be simplified.

Further, it is desirable that the photographic lens of the present invention further satisfies the following conditions.

v O-5<　-<　1　. 5 (4) however, fF: composite focal length of the front group.

Condition (4) defines the refractive power of the front group, and if the upper limit is exceeded, the refractive power of the front group becomes weaker and the total length of the lens becomes longer. On the other hand, if the lower limit is exceeded, the refractive power of the front group becomes too strong and aberrations worsen.

By the way, when the ratio of the refractive powers of the front group and the rear group is relatively small, i.e., in the range of -1: combined refractive power of the front group -, : combined refractive power of the rear group, the total length is In order to maintain a sufficient pack focus while keeping the lens short, it is necessary to increase the refractive power of both the front and rear groups, and in this case, it is desirable that the rear group lens satisfy the following conditions.

r, -r.

l: R,: Radius of curvature of the image-side surface of the fourth lens, r: Radius of curvature of the object-side surface of the fifth lens.

This condition is for correcting spherical aberration and astigmatism, and if the upper limit is exceeded, spherical aberration will be under-corrected and astigmatism will also increase. When the lower limit is exceeded, the spherical aberration tends to be excessive.

In addition, when the ratio of the refractive power of the front group and the rear group is relatively large, that is, when it is in the range of It is necessary to make the force relatively weak, and in this case, it is desirable that the image-side surface of the second lens and the object-side surface of the third lens in the front group satisfy the following conditions.

where r4=radius of curvature of the image-side surface of the second lens, r: radius of curvature of the object-side surface of the third lens.

This condition is for correcting spherical aberration and astigmatism, and if the upper limit is exceeded, spherical aberration will be overcorrected. If the lower limit is exceeded, the spherical aberration will fall to the under side, and the astigmatism will also increase.

Examples 1 to 5 of the present invention are shown in Tables 1 to 5 below.

Here, f is the focal length of the entire system, FNO is the open F value, r,
is the radius of curvature of the first surface counting from the object side, d is the distance on the i-th axial surface counting from the object side, and d is the number of objects. Table 6
shows the relationship between Examples 1 to 5 and each condition (1) to (6). 1 to 5 are cross-sectional views of Examples 1 to 5, respectively, and FIGS. 6 to 1θ are aberration diagrams showing various aberrations of Examples 1 to 5, respectively.

table 1 (Example 1) f -24,3 FNCL-4,5 curvature radius Shaft top surface spacing Refractive index (Nd) Atsbe number (νd) table (Example 2) f -24,3 FNO, -C5 curvature radius Shaft top surface spacing Refractive index (Nd) Atsbe number (νd) table (Example 3) f -24,3 FNO, -4,6 curvature radius Shaft top surface spacing Refractive index (Nd) Atsbe number (νd) table (Example 4) f=24.3 FNO, -4,1 curvature radius Shaft top surface spacing Refractive index (Nd) Atsbe number (νd) table (Example 5) f=24.3 FNO, -4,1 curvature radius Shaft top surface spacing Refractive index (Nd) Atsube number (shi d) table

[Brief explanation of drawings]

1 to 5 are cross-sectional views of photographic lenses of Examples 1 to 5 of the present invention, respectively, and FIGS. 1 to 5 are aberration diagrams showing various aberrations of the photographic lenses of the protrusions f111 to 5, respectively. It is. I @ Luns ■ 2nd lens m 3rd lens ■ 4th lens ■ 5th lens S Squeezer Minolta Camera Co., Ltd. Figure 4 ! ! 3°l. All B@/・F=4.0 無#translation difference i 弘し事Fig. 0 non-diagram, therefore distortion 0mu

Claims (1)

[Claims] (1) Consisting of two groups in order from the object side across the diaphragm: a front group with positive refractive power and a rear group with negative refractive power, and the front group is located from the object side. The rear group consists of, in order, a first positive meniscus lens with its convex surface facing the object side, a second negative single lens lens, and a third biconvex lens. A compact photographic lens consisting of five elements, characterized by the fourth lens being a positive meniscus lens and the fifth lens being a negative meniscus lens convex to the image side. (2) A photographic lens according to claim 1, which satisfies the following conditions. 0.05<d_6/f<0.50, where f: focal length of the entire system, d_6: air distance between the front group and the rear group. (3) A photographic lens according to claim 2, which satisfies the following conditions. 1.0<f_4/f<15.0 0<(r_7-r_8)/(r_7+r_8)<0.5
However, f_4: focal length of the fourth lens, r_7: radius of curvature of the object-side surface of the fourth lens, r_8:
Radius of curvature of the image side surface of the fourth lens. (4) The photographic lens according to claim 1, wherein focusing is performed by moving the front group.