JPS5820008B2 - Retrofocus Gatakouka Cleanse - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a retrofocus wide-angle lens for a single-lens reflex camera, which has an aperture ratio of 1:2.8, an angle of view of 75° or more, and a long back focus.

There are a few conventionally known retrofocus wide-angle lenses having a lens configuration of 7 elements in 7 groups as shown in FIG.

The purpose of the present invention is to provide a lens system that is composed of 7 elements in 7 groups, has a long back focus, and has a short overall length, making it compact.
Furthermore, it is an object of the present invention to provide a high-performance retrofocus type wide-angle lens with sufficient correction of astigmatism, a well-balanced photographic distance from infinity to short distances, and less distortion.

As shown in FIG. 1, the lens system of the present invention includes a positive meniscus lens having a convex surface facing the object side, and a second lens and a third lens having a negative meniscus lens having a convex surface facing the object side. The fourth lens is a biconvex lens, and the fifth lens is a biconcave lens.
The following conditions are satisfied with a seven-element configuration in seven groups, including a lens, a sixth lens that is a positive meniscus lens with a concave surface facing the object side, and a seventh lens that is a biconvex lens.

However, f is the focal length of the entire system, f2, r3 + +
-4, +r5+ r6+ r7. r13+r14 is the radius of curvature of the image-side surface of the second lens, each surface of the second and third lenses, the object-side surface of the fourth lens, and both surfaces of the seventh lens; 3 lenses, the lens interval between the third lens and the fourth lens, and d7 is the thickness of the fourth lens.

Among the above conditions, condition (1) defines the shape of the air lens between the first lens and the second lens, and if the lower limit of condition (1) is exceeded, it is difficult to correct distortion. In addition, since the difference in refractive power between both sides of the air lens becomes small, the effect of correcting off-axis aberrations becomes small.

Moreover, if the upper limit of condition (1) is exceeded, it is not only disadvantageous in maintaining the back focus for a long time, but also the refractive power of the second lens and the third lens needs to be increased because the refractive power of the second lens becomes strong. This is useful for correcting off-axis aberrations when used in dogs.

Not good.

Next, the air lens between the second lens and the third lens and the third lens.
Air lens spacing between the lens and the fourth lens d4. d
6 is defined by conditions (5) and (6).

If the upper limits of these conditions (5) and (6) are exceeded, the total length of the lens system becomes long.

In order to compensate for this drawback, it is necessary to reduce the thickness d7 of the fourth lens, but in that case, this d7 will exceed the lower limit of condition (7) that defines this.

As described above, if d7 exceeds the lower limit of condition (7), astigmatism in the periphery will increase.

On the other hand, if d7 exceeds the upper limit of condition (7), conversely, d4. If d6 is not made small, the total length of the lens system will be short.

And in order to reduce the total length, this d4. If d6 is made small, the lower limit of conditions (5) and (6) will be exceeded, and in that case, the backup power will be reduced.

It becomes difficult to correct various aberrations while maintaining a long period of time.

In this way, conditions (5), (6), and (7) are mutually related conditions, and are designed to achieve the best balance between making the lens system compact and correcting various aberrations. It is a condition.

Furthermore, conditions (2) and (3) are such that when a positive lens is placed in the first lens and condition (1) is applied to it, each subsequent surface has a preferable refractive power for off-axis rays. It is a condition.

If the lower limits of both conditions are exceeded, spherical aberration and astigmatism will occur significantly, and these cannot be corrected by other lens elements.

Furthermore, if the upper limit is exceeded, the negative refraction effect of the air lens made up of each surface defined by these conditions will weaken, making it impossible to correct spherical aberration and astigmatism in a well-balanced manner throughout the lens system. become.

For the above reasons, the shapes of the air lens between the second lens and the third lens and the air lens between the third lens and the fourth lens should be as shown in condition (2) and condition (3). is desirable.

Finally, condition (4) determines the shape of the seventh lens, and in this condition, r, 13 > o means that the object side surface of this seventh lens is convex with respect to the object. However, this is intended to increase the positive refractive power on this surface to enhance the effect on aberration correction.

In this way, after setting r 13 > O, we further set this condition (
In the condition of -r and 13/ of 4), if the upper limit is exceeded, the effect becomes weak, and if the lower limit is exceeded, the effect becomes too strong, which is not preferable.

In other words, when the upper limit is exceeded, the effect of correcting spherical aberration and astigmatism becomes small, and when the lower limit is exceeded, the effect of correcting these aberrations becomes too strong, making it difficult to maintain the balance of these aberrations. Correction of distortion aberration also becomes difficult.

Examples of the lens system of the present invention described above are shown below.

d9=7.44 n5=1.78472 v5=25
．． 7rtomo 190.721 d, o=6.61 r1□--115,253 d11=8.57n6=1.65844 v6”50
．． 9r12--50.919' d12=0.36 r, 3=513.004 d15-8.93n7=1.62299 v7=58
．． 1r, 4--121.112 Example 2 f = 100 1: 2.8 Angle of view 75.3°
f B= 133.968r, = 91.816 d, = 15.18 nl ””1.66998 v1
=39.3r 2= 167.669 d2= 0.54 r 3= 98.884 d3= 4.26 n2=1.62299 v2=58
．． 1r 4 = 38.876 d4 = 18.25 r5 = 110.985 d, -4,46n3 = 1.58913 v3 = 61.1
r a-44,404 φ d6 = 16.14 r 7 = 81.144 d7 = 44.29 n4 = 1.69350 v4 = 50
．． 8r 5-86.546 d 8= 10.65 r o-86,496 d, -7,38n5=1.78472 v5-25.7
r1o = 182.550 d1o = 6.61 rlt = -113,424 dl, = 8.57 n6 = 1.65844 v6 = 5
0.9r12--52.363 d1□-0,36 r, 3= 653.024 d13= 8.93 n7=1.62299 v7=5
8.1r 14--109.442 Example 3 f = 100 1: 2.8 Angle of view 75.3
fB=135.9641-1=91.653 d,-15,18n1=1.66755 v1=41.
9r2-189.490 d2=0.54 r3== 110.137 d3-4.32 n2=1.62041 V2-60.
3r4= 40.891 d4= 18.45 r5: 121.979 d5= 4.47 n3=1.58913 v3=61
．． 1r6= 43.946 d6= 16.52 r7”= 85.922 d7=53.60 n4=1.69350 v4=50
．． 8r8= -84,405 d8=10.66 rg --89,844 d9= 7.39 n5=1.78472 v5=25
．． 7r 1o""' 200.341 d1o= 6.61 ,, --118.636 ' d11= 8.57 n6=1.67003 V6
""47.3r1□--55,683 d1□-0,36 r, 3: 526.811 d13= 8.93 n7=1.62299 v7=5
8.1r14=116.447 Example 4 f = 100 1: 2.8 Angle of view 75.3
fB=134.643r1=108.107 dl-15,1801-1,66998v1-39.3
1”2==183.814 d2=0.54 1”3=96.440 d3=4.25 n2=1.62299 v2=5
8.1r4= 39.523 d4 = 18.26 r5= 110.648 d5= 4.46 n3=1.58913 v3=6
1.11”a= 47.323 d6=16.10 r7= 83.628 d7=46.71 n4=1.72000 v4=5
0.3r8−-87.641 d8=10.66 rg==sl,so.

do-7,37n5=1.78472 v5=25.7
The above is a detailed explanation, and each embodiment and FIGS.
As is clear from the aberration situation of each example shown in the figure, the retrofocus type wide-angle lens of the present invention has an aperture ratio of 1:2.8,
It is a long lens system with an angle of view of 75 degrees or more and a back focus of about 1.34 f, and various aberrations are well corrected.

Above all, astigmatism is sufficiently corrected, and the shooting distance is (
It is a high-performance lens system that provides well-balanced correction from distances (from 300 to 300 mm) to close distances, and also has low distortion.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the invention wide-angle lens, and FIGS. 2 to 6 are aberration curve diagrams of each example.

Claims (1)

[Claims] 1. A positive meniscus lens having a convex surface facing the object side, a second lens and a third lens having a negative meniscus lens having a convex surface facing the object side, and a fourth lens having a biconvex lens. and a fifth lens that is a biconcave lens, a sixth lens that is a positive menicus lens with its concave surface facing the object side, and a seventh lens that is a biconvex lens.
A retrofocus wide-angle lens that satisfies the following conditions. However, r2+ r3+ r41 r5+ r(34r
7. r131r14 are the image side surface of the second lun, and
radius of curvature of each surface of the lens, the third lens, the object side surface of the fourth lens, and both surfaces of the seventh lens, d4. d6 is the lens interval between the second lens and the third lens and between the third lens and the fourth lens, d7 is the thickness of the fourth lens, and f is the focal length of the entire system.