JPH01130116A - Photographic lens - Google Patents

Abstract

PURPOSE:To provide the title lens which is bright, is wide in angle of view and is small in size by forming the lens of 4-group 4-element constitution, disposing a stop at rear position thereof and constituting the lens so as to satisfy specific conditions. CONSTITUTION:This lens is of the 4-group 4-element constitution consisting of a 1st lens L1 consisting of a positive meniscus lens, the convex face of which is directed to an object side, the 2nd lens L2 consisting of a biconcave lens, the 3rd lens L3 consisting of a negative meniscus lens, the convex face of which is directed to an image side, and the 4th lens L4 consisting of a positive lens. The stop S is disposed at the rear position thereof and the conditions expressed by equation I are satisfied. In equation, r5 is the radius of curvature on the object side of the 3rd lens L3; r6 is the radius of curvature on the image side of the 3rd lens L3. The photographic lens which is as bright as about 2.8 F number, has the wide angle of view of about 64 deg. angle of view and about 1.1 telephoto ratio, is small in size and has the stop disposed at the rear position to well correct various aberrations is thereby obtd.

Description

Detailed Description of the Invention The present invention has a bright F number of about 2.8 and an angle of view of 64 mm.
This relates to a photographic lens with a rear aperture of 4 elements in 4 groups.

Conventionally, in lens systems with a rear aperture for lens shutters,
The Tetsusar type and triplet type are often used (although they have been used, but for lens systems with an F number of 2.8 class and a wide angle of view of 64@), the Tetsusar type, which has stable optical performance, is mainly used. This Tetsusar type has the third and fourth lenses cemented together, and at the cemented surface,
It has the characteristics of correcting spherical aberration and chromatic aberration, and controlling the Petzval sum by the difference in refractive index between the third and fourth lenses, and has good optical performance in terms of a bright aperture ratio and wide angle of view. ing.

On the other hand, without cementing the third and fourth lenses,
A new lens configuration with a group of four elements has been proposed.

For example, in JP-A-58-142309, an F number of 2.8 and an angle of view of 58'' are achieved by using a configuration in which the second lens is a negative menicus lens with its convex surface facing the object side.
Furthermore, in Japanese Patent Application Laid-open No. 121413/1983, the fourth lens is a double-concave lens, resulting in an F number of 2.8 and an angle of view of 6.
3″ has been achieved.

The present invention is a lens system consisting of four elements in four groups, with an F number of 2.
It is an object of the present invention to provide a photographic lens system having a rear aperture that is bright as about 8, has a wide angle of view of about 64, is compact with a telephoto ratio of about 1.1, and has a rear aperture that can effectively correct various aberrations.

The present invention will be explained in detail below.

As shown in FIG. 1, the photographic lens system according to the present invention includes, in order from the object side, a first lens (L,) consisting of a positive meniscus lens with a convex surface facing the object side, and a second lens (L,) consisting of a biconcave lens. , a third lens (L,) consisting of a negative meniscus lens with a convex surface facing the image side, and a fourth lens (L4) consisting of a positive lens, with a 4-element configuration in 4 groups, and a diaphragm (S) is placed at the rear. Satisfy the following conditions.

That is, by sharing the negative power of the second lens with the third lens, coma flare occurring on the object side of the second lens is reduced, and insufficient correction of higher-order spherical aberrations is reduced.

Furthermore, the object side surface of the third lens is concave toward the object side, and the second lens
．． The third lens forms a convex air lens to improve coma flare. The image side surface of the third lens is made convex toward the image side to prevent it from becoming too strongly negative on the premise that the basic power arrangement is not disrupted, making the third lens a negative meniscus lens convex toward the image side. becomes effective.

-0,35<-<-0,01 r5+r6 However, rS: Radius of curvature on the object side of the third lens (L,) r6: Radius of curvature on the image side of the third lens (L,).

As mentioned above, the photographic lens system according to the present invention has a third lens (
L,) is a negative meniscus lens with a convex surface facing the image side, which is a major feature not seen in the past. Conditional expression■
represents this shape characteristic of the third lens (L,). If the lower limit of conditional expression (2) is exceeded, spherical aberration will be undercorrected, and
It becomes difficult to correct inward coma aberration. On the other hand, conditional expression ■
If the upper limit of is exceeded, spherical aberration will be overcorrected and coma flare will increase, making correction difficult.

In the present invention, in order to better correct aberrations,
It is desirable that the following conditions also be satisfied.

■0.01<-”-<0.2 however, f2: Focal length of the second lens (L8) f,: Focal length of the third lens (L,) It is.

Conditional expression (■) is the ratio of the radius of curvature of the object side surface and the image side surface of the third lens (L,), and if the lower limit of this conditional expression (■) is exceeded, spherical aberration will be undercorrected and astigmatism around the angle of view will increase. This makes correction difficult. Moreover, when the upper limit of conditional expression (2) is exceeded, distortion becomes small, but spherical aberration becomes over-corrected, and conversely, astigmatism becomes under-corrected.

Next, conditional expression (2) defines the ratio of the focal lengths of the second lens L) and the third lens (L3), that is, the power distribution of the negative lens in the entire lens system, and this is set as an appropriate range. This corrects spherical aberration, image quality, and coma. If the lower limit of condition (2) is exceeded, spherical aberration will be overcorrected, and it will be difficult to correct inward coma aberration. Furthermore, if the upper limit of conditional expression (2) is exceeded, spherical aberration will be insufficiently corrected, coma flare will increase, and correction will become difficult.

By satisfying the above conditions, the third lens (L,)
It is a new type of lens system consisting of 4 elements in 4 groups, which uses a negative meniscus lens that was not used in the 2000s.It has a bright F number of about 2.8 and a wide angle of view of about 64 degrees.
It becomes possible to provide a photographic lens that is compact with a telephoto ratio of about 1.1 and has a rear aperture that can effectively correct various aberrations.

Examples of the present invention will be shown below. In the examples, L, , L2,
8. L4 is the lens number counted from the object side, rl...
r, is the radius of curvature of the surface counted from the object side, d,...d,
indicates the distance on the axial surface counted from the object side. A surface marked with * indicates an aspheric surface, and its shape is determined by taking the X coordinate in the direction of the optical axis, the Y coordinate in the direction perpendicular to it, and the paraxial curvature as rt.
When , it is expressed as DY"+EY'°+FY"+... Here, A, B, C,, D, E,
F, . . . are aspheric coefficients.

Further, in each example, f represents the focal length, F represents the F number, and 2ω represents the angle of view.

<Example 1> f=100.0 F=2.8 2ω=64'r,
36.583 d, 11.555 N, 1.78850 ν,
45.68rs 183°”84ti, 5.3□9
Nz1.6□339)/. 9.2゜rs 7
6.923 ds 3.638 N31.51B23 ν, 5
8.96rt 133.507 d, 7.196 N, 1.77250 νa
49.77ra 79.481 d@3.846 f, 00 r, *72.200 dy 7.136 N41.49140 shi4
57.82 YuEgo m=-o, t46"-=o, 745r
5+rb rb'-=0.1
10 Last 11 Old F defeat [Mi08O B=-0,1491X10-'C=-0,11673xlO-' D=0.22026X10 0 E=-0,31765xlO-"Noriou's birth diameter Supervisory plate plate 1 Nearest rate Eeni defeat d, ″
1.522 d< 4.943 d,, 1.282 ds 3.846 r9 ω mm [A=0.0 B=-0,14623X 10-'C=0.631
46X10-' D = -0,38880x LO-''E = 0.7
6408
3756xlO-” <Example 5> f=100.OF=2.8 2ω=64@curvature radius
On-axis spacing Refractive index Atsbe number r+ 33.
095 d, 11.735 N, 1.78831 SI47.
32rz 129.544 dz 1.231 ra-3058,478 d, 5.585 rs 76.923 ds 4.596 Ns 1.58400 Vs
31.00rh 102.564a, 0.571r? 90.229 d, 7.139 N41.491401/457
．． 82rs 72.613 d, 3.846 fq 00 i=-0,143i=0.750 A=0.0 B=0.32657X10-5 C=-0,13551X10-' D=0.87426xlO-10 E= -0.10771
1.111 da 5.686 d, 1.282 d, 3.846 fq (Xl rs rb -=-0,143 dishes=0.750 r6+rh r&A=0.0 B=-0,39713X 10-'C= 0.25
509X10-7 D=-0,16175X10-''E=0.28
860X10-1! r4 00 rs 16 r5+ra = '・077 Otsu-=0・857
A=0.0 B=0.45877X10-'C=-0,62032x10-'D=0.5
1900 X 10- 'E=-0, 12530X10
−”Diameter of birth of Kojigami plate Farm Placement rate Atsube number d,
5.651 d, 1.282 fq 00 -”-=0.069 f3 Miss 110 direct loss A=0.0 B=-0,2130510-' C=0.95139X 10-" D=-0,15814XIO- 'E=0.40541X10-'' Figure 1 shows an outline of the lens configuration corresponding to the above embodiment, and Figures 2 to 9 are aberration diagrams of Examples 1 to 8. , the solid line (d) represents the aberration for the d-line, and the dotted line (SC) represents the sine condition.

Further, the dotted line (DM) and the solid line (DS) represent astigmatism on the meridional plane and the sagittal plane, respectively.

[Brief explanation of the drawing]

The figures are all related to the present invention, and FIG. 1 is a lens configuration diagram, FIG. 2, FIG. 3, and FIG. 4. FIG. 5, FIG. 6, FIG. 7, FIG. 8, and FIG. 9 are aberration diagrams of each example.

Claims (1)

[Claims] (1) In order from the object side, the first lens consists of a positive meniscus lens with a convex surface facing the object side, the second lens consisting of a biconcave lens, and the negative meniscus lens with a convex surface facing the image side. 4th lens group 4 consisting of 3rd lens and positive lens
What is claimed is: 1. A photographic lens having a lens configuration, having a rear aperture, and satisfying the following conditions. -0.35<r_5-r_6/r_5+r_6<-0.
01 However, r_5: radius of curvature on the object side of the third lens r_6: radius of curvature on the image side of the third lens (2) The photograph according to claim 1, which satisfies the following condition. lens. 0.5<r_5/r_6<0.98 0.01<f_2/f_3<0.2 However, f_2: Focal length of the second lens f_3: Focal length of the third lens