JPS59143116A - Gauss type lens - Google Patents

Abstract

PURPOSE:To obtain a Gauss type lens having a small change of aberration due to focusing by satisfying the prescribed conditions for a lens system consisting successively a front group of positive, positive and negative lenses and a rear group of a cemented lens of negative and positive lenses and a positive lens respectively from the side of a subject. CONSTITUTION:This lens system contains a front group of the positive, positive and negative lenses and a rear group of a cemented lens of negative and positive lenses and a positive lens and performs focusing by moving the front group of lenses. Here the conditions of equations I -VI are satisfied for said lens system. In this case, fF and fR show the focal distances of front and rear lens groups respectively, (f) is the focal distance of the whole lens system, (l) is an air space between the front and rear groups, Ri and Ni are the curvature radius of the surface of the i-th lens and the refractive index of the lens glass material to a line (d) and Di is the thickness or an air space between the surfaces of the i-th and (i+1)th lenses. In such a way, it is possible to obtain a Gauss type lens having a small change of aberration due to focusing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens system, and more particularly to a Cow type lens that performs focusing by moving part of the lens group of the lens system.

Conventionally, so-called Gaussian lenses have been widely used as standard lenses for single-lens reflex cameras, for example.The reason for this is that the angle of view generally required for standard lenses for single-lens reflex cameras is 2W==45° is relatively easy to guarantee good image quality over the entire screen in any shooting range of the TJ stand, and the F number F/l1=2 is also required for single-lens reflex cameras. This is because the back focus can also be secured for a relatively long time.

By the way, in many Gauss type photographic lenses, focusing is generally performed by moving the entire lens system. This is because there is an advantage that aberration fluctuations due to focusing are relatively small. however,
Since the entire lens system is moved, a large driving force is required to drive the lens system, and the lens barrel also becomes complicated and large.

Therefore, it is required to perform lens focusing with a small driving force. For example, this is very inconvenient as an autofocus photographing lens. Therefore, it is necessary to move some of the lens groups in the lens system to perform focusing and reduce the driving force of the lens groups. However, when using this method in the past, there was a problem in that large aberration fluctuations occurred due to focusing.
For example, in the embodiment of the Gaussian photographic lens disclosed in Samurai Kaisho 52-146620, the f of the lens 1 behind the aperture is 16 f (f is the focusing value of the entire system). It is possible to focus up to any object distance without interfering with the lens group in front of the aperture.

However, as the focus is focused on a near-distance object point, spherical aberration becomes insufficiently corrected, and significant outward coma aberration occurs from the center of the screen to the periphery of the screen. This extroverted coma aberration still remains even when the aperture is closed down to make it darker, and it has a serious effect on imaging performance, which is a serious problem.

The present invention was made in view of the above-mentioned circumstances, and provides a Gauss-type lens that can perform focusing with a small driving force, has little variation in aberrations due to focusing, and is suitable as a photographic lens for metofocus, for example. The purpose is to obtain.

Photographic lens lens (Δ
The characteristics of the formation are that, in order from the object (1111),
The second lens group has a positive refractive power with a convex surface facing the ll, and the second lens group has a negative refractive power with a strong concave 1I11 turned toward the image plane. It has a rear jj, f: consisting of a fourth lens group in which lenses with negative and positive refractive powers are combined and a fifth lens group with positive refractive power, and focusing is performed by moving the groups afterwards. That's true.

1) When moving the IJ rear group and performing July power lensing, in order to prevent the rear group from mechanically interfering with the front group located in front of the aperture at the close distance 1 = iiE object point, It is necessary to secure a certain amount of air gap between the front and rear groups when the object point is at infinity, and to strengthen the refractive power of the rear group to reduce the amount of movement when focusing on the object point at close range. It is essential to make it smaller. For this purpose, the focal length of the front group is fF lThe focal length of the rear group is /R1 The focal length of the entire system is f,
When the air distance between the front group and the rear group is l, it is preferable to satisfy the following condition. The contents of the conditional expression are explained below.

Conditional expression (1) is to prevent the mechanical interference between the front group and the rear group mentioned earlier.If the lower limit of conditional expression (1) is exceeded, mechanical interference is likely to occur, and if the upper limit is exceeded, If it exceeds the total length, the total length will become longer and the compactness will be lost.

Conditional expression (2) is related to conditional expression (1), and with respect to the focal length of the front group, if the upper limit of conditional expression (2) is exceeded, l cannot be increased as the refractive power of the rear group is strengthened. If the lower limit is exceeded, the refractive power of the front group becomes stronger, making it difficult to correct aberrations.

Conditional expression (6) concerns the ratio of the focal lengths of the front group and the rear group.If the lower limit of conditional expression (b) is exceeded, it is good for preventing mechanical interference, but the refractive power of the rear group becomes stronger and Positive A, II
Unless a glass material with a high refractive index is used for a lens with a high refracting power, it will be difficult to correct aberrations. On the other hand, if the upper limit of conditional expression (6) is exceeded, the closest distance cannot be shortened.

The present invention adopts the above lens shape and refracting power arrangement, and when focusing is performed with the rear group, the extension piece is small, the lens group for focus sync' is unsuitable, and the lens group for autofocus has a small VY power. A suitable lens system can be obtained.

In the present invention, when the above configuration is adopted, it is preferable to satisfy the following conditions in order to perform even better aberration correction.

That is, in order from the object side, the radius of curvature of the i-th lens surface is number 8, the thickness or air gap between the ith lens surface and the t+1-th lens surface is number D, and the glass material constituting the second lens is The objective is to satisfy the following condition when Ni is the refractive index for d fJ.

Since the rear group is located far away from the aperture, barrel-shaped distortion is noticeable. In order to correct this before and after, the closer the upper limit of conditional expression (4) is, the better the temperature is.However, if the upper limit is exceeded, it becomes difficult to correct spherical aberration, and conversely, conditional expression (4)
If the lower limit of 4) is exceeded, barrel distortion at an object point at infinity cannot be well corrected.

Conditional expression (5) relates to the refractive index of the glass material of the positive refractive power component of the rear group. If the lower limit of conditional expression (5) is exceeded, it is difficult to set the Petzval interest rate, J., and it is difficult to correct the field curvature. On the other hand, if the upper limit of conditional expression (5) is exceeded, aberrations can be easily corrected, but the curvature of the glass increases and the cost of the glass material increases, which is not preferable.

Conditional expression (6) relates to the bonding of the bonded lenses in the rear group, and if the lower limit of conditional expression (6) is exceeded, spherical aberration will be insufficiently corrected and fluctuations in coma aberration due to focusing will also become large. - If the upper limit of conditional expression (6) is exceeded, the overcorrected spherical aberration becomes difficult to correct.As shown in the figure above, the present invention allows easy focusing and achieves good aberration correction. is obtained.

Next, numerical examples of the present invention will be shown. In numerical examples R
2 is the radius of curvature of the i-th lens surface in order from the object side, D
i is the th lens thickness and air spacing in order from the object side,
Ni and νt are the refractive index and Abbe number of the glass material of the 1st lens from the object side, respectively.

Numerical Example 1 Focal length Lζ [L=100 F/16, 1:1.8
2w=45.5°R12 52.1250 DI=
8.849 Nl2 1.61484 ν1=51
．． 2R2= 295,4654 Dz== 0.29
1R32 44.2425 D 326,572
N2=1,713 C2253.8R4=76
．． 3352 D 42 2,742R5 2 132,6
518 D s = 2.464 N 3 = 1.6
6446 Shi32 35.7R6: 30,0311
D6=27,557R7: -30,5915D7
22,815 N4:1,7847 shi4226
．． 2R8=-161.2934 DB-=-10,9
23N5=1,804 Shi5=46.6R9= -4
0,0011D92 0.291F (10=273,
1048 L) 102 6,483 N6=1,8
83 White: 40.8R11 knee 123.417
7 fF= 228.472 Lens total length = 69.3873 fp-=
93.843 Bank Focus-70,5668 The cross-sectional view of Numerical Example 1 is shown in Fig. 1, the aberration diagram for an object point at infinity is shown in Fig. 4 (a), and the aberration diagram at 12f when the focal length is f. It is shown in Figure (1)l.

Numerical Example 2 Focal length = 100 Fag, 1:1.8 2w =
45.5°R1=-=50.4294 D1=9.
148 Nl2 1,66672 ν48.3R2
= 265.828OL+2= 0.290R3=
42.6458 D 325.256 1i221.
6968 ν2=55.5R4=69.3(1
76D4=3.605R52130.9044D
5= 2.013 N32 1.6668 νa=
3a.

R6 = 29.4059 D6 two 27,279R7
= -30,3205D723,387 N4=1.
7552 Shi4=27,5I (8=-117,01
18D8=10,220 N52 1.7725
C5 = 49.6 R9 Knee 30.5173 D9 = 0
．． 290R10= 257,1952 Lh02 6
,119 N6=1,83481 White: 42.
7 ratio 1 = -117,0582 fF = 227.806 Lens total length -67,6071R = 94.50
9 Backforce Canu=7[J, 60U A cross-sectional view of Numerical Example 2 is shown in FIG. 2, an aberration diagram for an object point at infinity is shown in FIG. 5 (al), and an aberration diagram at 14f is shown in the same figure (b).

Numerical example Focal length = 100 FA +1'l-82t# = 4
5.5゜R12 52,0891 DI=8.80
2 N1=1,61484 ν1=51.2R2=
282.5601 D220,291R3= 44
．． 3469 D3=6.986 N2=1.71
3 ν2 = 53.8R4 = 75.7829
D4=2.729R52131.3508 D5=
2,899 N5=1,66446 C3-=3
5.7Ra=29.8934 D6227,37
2R7=-30,5853D722.934 N4=
1,7552 Shi4-27.5R8=-145,0
52308=-10,700N 5=1.7725
νs = 49, aR9 knee 40.2946 Dc
+= 0.291RIO2 245.0155DIO
26,477 N62i, 83481 624
2.7R11-=-113,5155 Lens total length =69.428 fF2234.68
1 bank focus = 70.289 fn2 1 f2.692 The cross-sectional view of Numerical Example 6 is shown in Fig. 6, and the aberration diagram for an object point at infinity is shown in Fig. 6. Shown in (b).

[Brief explanation of the drawing]

FIGS. 1 to 6 are cross-sectional views of lenses of Numerical Embodiment 1 to Numerical Embodiment B of the present invention, respectively.
J lFigure 6 (a) + (b)'U is a diagram of various aberrations when the object of Numerical Examples 1 to 6 of the present invention is at infinity and when it is at close distance. S represents sagittal image curvature. Patent applicant Kinon Corporation IFc)C(Is Figure 2)

Claims (2)

[Claims] (1) Starting from the object side, the first lens group has a positive refractive power with a convex surface facing the object side, the second lens group also has a positive refractive power with a convex surface facing the object side, and a strong C/concave surface faces the image side. A front group consisting of a 6th lens group with a negative refractive power facing towards the object, a 4th lens group consisting of lenses with negative and positive refractive powers with a strongly concave surface facing the object side, and a 5th lens with a positive refractive power. Focusing is performed by moving the rear group, and the focal length of the front group is f F l The focal length of the rear group is f R
+ When the focal length of the entire system is f and the air distance between the front and rear groups is l, (1) 0-26 <A< [J, 28 (212,1<
Gaussian lens 0 characterized by satisfying the condition L<2.4 (2) From the object side, the radius of curvature of the t@th lens surface is R2, the wall thickness or air gap between the tth and i+1th lens surfaces is Dt, and the glass material constituting the seventh lens is d
Patent claim +7)N satisfying the following condition when the refractive index for a line is Ni
The Gaussian lens described in Item 1 of Box i.