JP2811447B2 - Macro lens - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a macro lens having an aperture ratio of about 2.8 and an angle of view of about 28 ° capable of photographing from an object at infinity to an object having an imaging magnification of about 1: 2. It is.

(Conventional technology and problems) Since the conventional macro lens has a large moving amount of focusing, the lens barrel has to be lengthened even if the optical length is shortened, and it is hard to say that the lens is compact. In addition, in order to make autofocus effective with the advent of an autofocus camera, a macro lens that can obtain a large photographing magnification with a small amount of extension is desired.

Conventionally, Japanese Patent Application Laid-Open No. 61-264312 and the like have tried to realize a large photographing magnification with a small feeding amount, but it was hard to say that the feeding amount was small and was unsatisfactory in terms of downsizing.

In the present invention, the focusing speed is increased by reducing the amount of extension to less than half compared to the conventional focusing by the entire extension, thereby realizing a mechanically and optically compact size, and an aberration variation at all imaging magnifications is extremely reduced. It provides a small number of macro lenses.

(Means for Solving the Problems) In the present invention, focusing is performed by moving the first group of positive power to the object side, and the aberration deterioration caused by the change of the object distance is caused by the second group of negative power with respect to the image plane. The correction is performed by moving the lens fixedly or nonlinearly. With this configuration, compactness can be achieved, and the first principal point of the entire system shifts to the object side during focusing, so that a sufficient working distance is secured.

Further, the first lens group has a positive, negative, positive configuration to correct distortion, and a compact lens is achieved by satisfying the following conditional expression.

0.15 <α <0.3 ………… However, here f: focal length of the entire system, Δx: amount of movement of the first unit with respect to the image plane at an imaging magnification of 1: 2, LT: distance from the first surface at infinity to the image plane.

The first group is composed of, in order from the object side, a first group having positive power, a first group having one negative lens, and a first group having positive power.
The image group was made compact by satisfying the following conditional expressions.

0.45 <f ₁ a / f <1.0 ……… 0.35 <| f ₁ b / f | <0.7 ……… 0.35 <f ₁ c / f <0.52 ………, where, f: whole system focal length of, f ₁ a: the focal length of the 1a group, f ₁ b: the focal length of the 1b group, f ₁ c: is the focal length of the 1c group.

Further, the air gap between the first group and the first group in the first group was changed during focusing, and the second group was composed of at least two positive lenses and two negative lenses.

(Function) The product α of the tele ratio, which represents the compactness of the overall optical length, and the value obtained by normalizing the extension amount relating to the mechanical overall length by the focal length is considered to be an index indicating the responsiveness and compactness of the autofocus. However, by giving the value of α to the conditional expression, the overall optical length can be reduced, and the overall mechanical length can also be reduced.

If the lower limit of the conditional expression is exceeded, further compactness can be achieved, but it is difficult to correct sagittal coma and increase the diameter. When the value exceeds the upper limit of the conditional expression, the moving amount increases, and it is difficult to reduce the size.

The conditional expression stipulates the power arrangement of each group constituting the first group for maintaining the aperture ratio of 2.8 and achieving compactness and high performance.

When the lower limit of the conditional expression is exceeded, the aperture ratio of the first subunit itself becomes small, and it becomes very difficult to correct spherical aberration and coma with a small number of lenses. Conversely, if the upper limit of the conditional expression is exceeded, it becomes difficult to make the first lens unit compact.

Next, the conditional expression relates to the flatness of the image plane due to a change in the object distance. If the lower limit of the conditional expression is exceeded, the Petzval sum becomes excessively negative, and it becomes difficult to correct the Petzval sum. In addition, if the power of the second lens unit is weakened, the Petzval sum can be corrected, but the telephoto ratio is undesirably increased. If the upper limit of the conditional expression is exceeded, it becomes difficult to make the system compact.

If the lower limit of the conditional expression is exceeded, the power of the second lens unit must be increased in order to secure the air gap between the first lens unit and the second lens unit, which makes it difficult to secure positive distortion correction and back focus. If the upper limit of the conditional expression is exceeded, the moving amount becomes large, and it is difficult to make the camera compact. Further, by constituting the second group with at least two positive lenses and two negative lenses,
The degree of freedom of the selection of the refractive index is increased, and the second group is prevented from increasing the Petzval sum negatively, and at the same time, it is easy to correct positive distortion by downsizing. If the air gap between the first and second lens groups is floated during focusing, astigmatism at short distances can be controlled, and higher performance can be achieved.

(Examples) Table 1 below shows the relationship between Numerical Examples 1 to 5 according to the present invention and various numerical values relating to each Numerical Example.

In the numerical examples, f is the focal length, Fno is the F-number, ri
Is the radius of curvature of the ith lens surface from the object side, di is the distance on the ith axis from the object side, ni is the refractive index of the ith lens from the object side, and νi is the ith lens from the object side. Is the Abbe number of the lens.

In Table 1, Δx is the amount of movement of the first lens unit with respect to the image plane at an imaging magnification of 1: 2, LT is the distance from the first surface at infinity to the image plane, f is the focal length of the entire system, f ₁ a is the focal length of the 1a group, f ₁ b is the focal length, f ₁ c of the 1b group is a focal length of the 1c group.

(Effect) The macro lens of the present invention satisfies the above conditions to reduce the optical overall length and the mechanical overall length while maintaining the aperture ratio of 2.8, so that the focusing feed amount suitable for an autofocus camera can be reduced. A small, high-performance macro lens with very little aberration variation at all imaging magnifications was obtained.

[Brief description of the drawings]

1 to 4 are lens configuration diagrams of Numerical Examples 1 to 4 of the present invention, respectively, and FIGS. 5 to 8 are Numerical Embodiments 1 of the present invention, respectively.
It is an aberration figure showing various aberrations of-. (A) and (B) in the lens configuration diagram and the aberration diagram are respectively a lens configuration diagram and an aberration diagram at the time of infinity focusing and at the close distance focusing. In the lens configuration diagram, I is the first group, II is the second group, a is the 1a group, b is the 1b group, c is the 1c group, S is the aperture, ΔM is the meridional image plane, and ΔS is It is a sagittal image plane.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-195617 (JP, A) JP-A-62-227111 (JP, A) JP-A-62-18513 (JP, A) JP-A-61-18513 132916 (JP, A) JP-A-61-67815 (JP, A) JP-A-60-188917 (JP, A) JP-A-62-160412 (JP, A) JP-A-61-238010 (JP, A) JP-A-61-138912 (JP, A) JP-A-55-28038 (JP, A) JP-A-63-179308 (JP, A) JP-A-63-147126 (JP, A) (58) (Int.Cl. ⁶ , DB name) G02B 9/00-17/08

Claims (3)

(57) [Claims] 1. A first lens unit having a positive power, comprising a first lens unit having a positive power, a first lens unit having a single negative lens, a first lens unit having a positive power, and a negative lens unit. Composed of a second lens group having the power of
The group moves to the object side, and the second group moves fixedly or non-linearly with respect to the image plane, and 0.15 <α <0.3 ………… 0.45 <f1a / f <1.0 ………… 0.35 <| f1b / f | <0.7 ………… 0.35 <f1c / f <0.52 ………… Macro lens characterized by satisfying the following condition; f: focal length of the entire system at infinity of the object distance, Δx: amount of movement from the infinity of the object distance to the image surface of the first group at an imaging magnification of 1: 2, LT: from the first surface to the image surface at infinity , F1a: focal length of the first lens group, f1b: focal length of the first lens group, f1c: focal length of the first lens group. 2. The first unit is composed of, in order from the object side, a first unit having positive power, a first unit having one negative lens, and a first unit having positive power. 2. The macro lens according to claim 1, wherein the air gap of said lens changes during focusing. 3. The macro lens according to claim 1, wherein the second group includes at least two positive lenses and two negative lenses.