JP2003241080A - Large aperture ratio lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large aperture ratio lens which is a modified Gauss type large aperture ratio lens having a six-group and seven-piece constitution and constituted with parameters numerically very different from those of the conventional system, besides, wherein a sagittal coma flare is reduced. <P>SOLUTION: The large aperture ratio lens is constituted of a 1st lens L1 having a positive refractive power, a 2nd meniscus lens L2 having a positive refractive power and whose convex side faces an object, a 3rd lens L3 having a negative refractive power, a 4th lens L4 having a negative refractive power and whose deep concave side faces the object and which is joined to a 5th lens L5 having a positive refractive power, a 6th meniscus lens L6 having a positive refractive power and whose convex side faces an image and a 7th lens L7 having a positive refractive power in this order from the object side, and the large aperture ratio lens satisfies a fixed condition. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-diameter ratio standard lens of an interchangeable lens for a 35 mm single-lens reflex camera. 2. Description of the Related Art Conventionally, a large aperture ratio standard lens having an F number of 1.4 class for a 35 mm single-lens reflex camera is mostly a modified Gaussian type having six groups and seven lenses, and each parameter is extremely large. It is composed of close numbers. In order to obtain the back focus required for the mirror up, the group before and after the diaphragm has an asymmetric power distribution, and the front group has evolved into a form in which the junction surface is separated. [0003] However, even though many attempts have been made to date, it cannot be said that all systems have sufficiently compensated for sagittal coma, which is a Gaussian type problem. Was something. Accordingly, the present invention provides a large-diameter ratio lens of a modified Gaussian type composed of seven elements in six groups with parameters which are numerically significantly different from those of the conventional system, and which has a reduced sagittal coma flare. It is an object of the present invention to provide a specific lens. [0005] In order to achieve the above object, the present invention provides a first lens L1 having a positive refractive power and a convex surface having a positive refractive power and having a positive refractive power. Meniscus-shaped second lens L2, third lens L having a negative refractive power
3. The fourth lens L4 having a negative refractive power with a deep concave surface facing the object side and the fifth lens L5 having a positive refractive power are cemented,
A meniscus sixth lens having a positive refractive power with the convex surface facing the image side
The lens L6 includes a seventh lens L7 having a positive refractive power, and satisfies the following condition. (1) 0.8f <f12 <f (2) 0.16f <D5 <0.25f (3) 0.45f <R6 <0.62f (4) 1.3 <| R6 / R8 | <1.62 Where f: focal length of the entire system f12: composite focal length of the first lens and the second lens D5: center thickness of the third positive lens R6: radius of curvature of the rear surface of the third lens R8: radius of curvature of the front surface of the fourth lens is there. [0006] One of the features of the present invention, the first,
The point is that the power of the combined system of the lens L1 and the second lens L2 is significantly reduced as compared with the conventional modified Gaussian type having six groups and seven elements. Conditional expression (1) is a condition that defines the power of the combined system of the first lens L1 and the second lens L2, and guarantees conditional expression (3) that makes the radius of curvature of the rear surface of the third lens L3 large. It is also a condition. If the lower limit of the conditional expression (1) is exceeded, the combined power of the first lens L1 and the second lens L2 becomes strong, so that the power arrangement becomes close to that of the conventional modified Gaussian type, and the defect of the Gaussian type cannot be corrected. Conversely, if the combined power becomes smaller than the upper limit, the negative power of the third lens L3 must be further weakened in order to balance the front group. As a result, the Petzval sum becomes larger and the aberration correction becomes larger. It is not preferable because the burden is placed on the rear group. Conditional expression (2) requires that the center thickness D5 of the third lens L3 be much larger than the conventional modified Gaussian type. By increasing the center thickness D5 of the third lens L3, curvature of field and astigmatism can be satisfactorily corrected. Conditional expression (1), conditional expression (2) and conditional expression (3)
Are inseparable from each other and do not exceed the lower limit if conditional expressions (1) and (2) are satisfied. Exceeding the upper limit is not preferable because the size of the system is increased, and tends to increase coma flare. [0008] Conditional expression (3) defines the radius of curvature R6 of the rear surface of the third lens L3. By increasing the radius of curvature of the radius of curvature R6 on the rear surface of the third lens L3 within the range of the conditional expression (3), it is possible to suppress the occurrence of sagittal coma flare. When the value exceeds the lower limit, the sagittal coma flare correction effect is not sufficient. When the value exceeds the upper limit, flare removal is good, but spherical aberration is difficult to correct, and it is not preferable because correction of symmetric aberration is hindered. Condition (4) defines the relationship between the radius of curvature R6 on the rear surface of the third lens L3 and the radius of curvature R8 on the front surface of the fourth lens L4. The present invention breaks the symmetry of the deformed Gaussian type shape, but appropriately sets the radius of curvature R8 on the front surface of the fourth lens L4 in response to the increase in the radius of curvature R6 on the rear surface of the third lens L3. is necessary. If the lower limit is exceeded, the configuration becomes close to that of the conventional Gaussian type, and the effect of flare correction is reduced. When the upper limit is exceeded, the front surface of the fourth lens L4 becomes a strong concave surface, but the positive power of the rear group also increases at the same time, so that it becomes difficult to correct off-axis aberrations including spherical aberration, which is not preferable. Hereinafter, numerical examples 1 and 2 of the lens according to the present invention will be described. The large aperture ratio lens according to the present invention includes, in order from the object side, a first lens L1, a second lens L2, and a third lens L2.
It comprises a lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. Also,
In each embodiment, f is the focal length, Fno is the F number, ω is the angle of view, the number is the order of the lens surface from the object side, R
(I) indicates the radius of curvature of the lens surface, and D (I) indicates the lens interval. Numerical Example 1 f = 51.59 Fno = 1.41 ω = 23.1 ° Number R (I) D (I) ND Vd [1] 94.86 5.14 1.8042 46.5 [ 2] -238.53 0.1 [3] 41.42 3.43 1.8042 46.5 [4] 88.92 1.76 [5] -669.33 9.46 1.595551 39.2 [ 6] 26.91 5.14 [7] 0 6.64 [8] -19.29 1.56 1.7736 29.5 [9] 95.8 8.48 1.755 52.3 [10] − 28.59 0.1 [11] -176.98 3.43 1.8042 46.5 [12] -49.28 0.1 [13] 152.67 3.01 1.8042 46.5 [14] -138.52 Conditional expression (1) f12 / f = 0.87 (2) D5 / f = 0.18 (3) R6 / f = 0.52 (4) | R6 / R8 | = 1.40 Numerical Example 2 f = 51.6 Fno = 1.41 ω = 23.1 ° Number R (I) D (I) ND Vd [1] 133.36 3.62 1.8042 46.5 [2]-170.5 0.1 [3] 45. 65 3.31 1.8042 46.5 [4] 114.122 [5] -245.8 11.87 1.559551 39.2 [6] 29.91 4.58 [7] 0 6.91 [ 8] -19.01 1.58 1.771729.5 [9] 130.89 8.13 1.755 52.3 [10] -27.1 0.1 [11] -229.91 3.31 1.8042 46.5 [12] -53.49 0.1 [13] 142.3 2.96 1.8042 46.5 [14] -154.01 Conditional expression (1) f12 / f = 0.9 (2) D5 / f = 0.23 (3) R6 / f = 0.58 (4) | R6 / R8 | = 1.57 The lens of the present invention is a modified Gaussian type lens. The shape of the front and rear group while inheriting the configuration By breaking the symmetry in new ways, and can be implemented to differentiate a prominent Gaussian type system of the above specifications, reduce sagittal flare, it is possible to increase constituting the radius of curvature of each surface at the same time. In addition to the performance of a Gauss-type system of the same specification, it will be easier to manufacture and reduce costs.

[Brief description of the drawings] FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention. FIG. 2 is an aberration diagram of a numerical example 1 of the present invention. FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention. FIG. 4 is an aberration diagram of a numerical example 2 of the present invention. [Explanation of symbols] L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens

Claims (1)

1. A first lens having a positive refractive power, a meniscus-shaped second lens having a positive refractive power and having a convex surface facing the object side, and a negative lens having a negative refractive power in order from the object side. A third lens, a fourth lens having a negative refractive power with a deep concave surface facing the object side and a fifth lens having a positive refractive power are cemented, and have a meniscus shape having a positive refractive power with the convex surface facing the image side. A large aperture ratio lens comprising a sixth lens and a seventh lens having a positive refractive power, and satisfying the following conditions. 0.8f <f12 <f 0.16f <D5 <0.25f 0.45f <R6 <0.62f 1.3 <| R6 / R8 | <1.62 where f: focal length of the entire system f12: The combined focal length of the first lens and the second lens is D5: the center thickness of the third positive lens R6: the radius of curvature of the rear surface of the third lens R8: the radius of curvature of the front surface of the fourth lens.