JPH0711625B2 - Telephoto macro lens - Google Patents

Description

The present invention relates to a telephoto macro lens having a focal length of f = 100 mm as an interchangeable lens for a 35 mm single-lens reflex camera, which is capable of photographing an object from infinity to a very close distance, especially at an equal magnification. It is a thing.

Conventionally, the entire feeding method has been used as the focusing method for macro lenses, but with the development of large-aperture McLens with a focal length of 50 mm class and macro lenses with a focal length of 200 mm class, various floating methods and internal methods have been adopted. Has been adopted. In general, various floating methods have been proposed for large-diameter macro lenses with an F number (F No.) 2.8 and a focal length f = 5.0 mm, mainly for the purpose of correcting coma aberration at the time of proximity. On the other hand, in a telephoto macro lens of f = 200 mm, a moving amount up to 1 × requires 200 mm in the whole feeding method, so the internal method is mainly used for the purpose of reducing the moving amount.

Japanese Patent Application Laid-Open No. 56-107210 discloses a proposal aiming at increasing the aperture and reducing the amount of focusing movement even in the telephoto macro lens of f = 100 mm which is the target of the present invention.
In this proposal, a floating method is used to increase the aperture, and a negative lens group is arranged on the image surface side to reduce the amount of focusing movement by strengthening the refractive power of the moving lens group. There is. However, if the shooting magnification is increased with such a configuration, the focal length of the entire lens system decreases, and the working distance, which is an advantage of the telephoto macro lens over the standard macro lens, is large and perspective distortion is small. Etc. will be offset. Therefore, as a result, it is extended to about 0.5 times without making it possible to shoot close-up up to 1 times,
After that, whether to deal with poor operability of the intermediate ring,
There is a problem of whether to adopt a configuration that achieves the same magnification even if the value of the telephoto macro lens is lost.

The present invention provides a telephoto macro lens that secures a necessary working distance as a telephoto McLens, in which the focal length hardly changes even at the same magnification, and the focusing movement amount which is important in operability can be reduced. Is. A further object of the present invention is to provide a telephoto macro lens which has a small deterioration in imaging performance from infinity to the same magnification and which is suitable for a large aperture.

Then, in order to achieve the above object, the lens system according to the present invention, as shown in FIG. 1 to FIG.
The first lens group (I) has a positive refractive power, the second lens group (II) has a negative refractive power, and the third lens group (III) has a positive refractive power. At the time of focusing from a long distance to a short distance, an air gap between the first lens group (I) and the second lens group (II) and the second lens group (II) and the third lens group (III) All the lens groups of the first lens group (I) to the third lens group (III) are caused to move differently so that the air space between them increases and decreases respectively at the maximum macro magnification, and the following conditions are satisfied. It is characterized by satisfying the formula.

(1) 1.1 <f / f ₁ <1.7 (2) 0.15f <D ₂₃ <0.4f where f is the focal length of the entire system when focusing on infinity, and f ₁
Is the focal length, axial air distance between the D ₂₃ and the second lens group upon focusing on infinity (II) and the third lens group (III) of the first lens group (I). Hereinafter, each conditional expression will be described in detail.

Conditional expression (1) is a condition that defines the focal length of the first lens group. If the lower limit of conditional expression (1) is exceeded, aberration correction will be easy, but the amount of focusing movement will be approximately the same as that of the conventional total feeding method, and this will undesirably increase the size of the lens system. On the other hand, if the upper limit of conditional expression (1) is exceeded, the amount of focusing movement will decrease and the size will be reduced, but spherical aberration, astigmatism, and distortion will be extremely difficult to correct, and it will not be possible to increase the aperture.

Conditional expression (2) defines the axial distance between the second lens group (II) and the third lens group (III) when focusing on infinity. If the lower limit of conditional expression (2) is exceeded, it will be easy to correct aberrations and secure peripheral light amount when focusing on infinity,
In order to effectively use this change of D ₂₃ depending on the shooting distance to reduce the amount of focusing movement, the second lens group (II)
And the refractive power of the third lens group (III) must be strengthened together. This makes it difficult to correct spherical aberration and astigmatism balance and coma aberration at photographing magnifications up to 1 ×, which is not desirable for increasing the aperture. However, unless the refracting powers of the second lens group (II) and the third lens group (III) are both strong, the focusing movement amount increases and the object of the present invention is not satisfied. On the other hand, if the upper limit of conditional expression (2) is exceeded, the size of the lens will have to be increased in order to secure the amount of peripheral light, and positive distortion will become noticeable in the vicinity of unity magnification, causing problems as a macro lens. Become.

In carrying out the present invention, it is desirable that the following conditional expressions are further involved.

(3) 0.35 <f / f ₁₂ <0.85 (4) 1.2 <f ₂₃ /f<5.0 where f ₁₂ is the first lens group (I) and the second lens group (II when focusing on infinity). ) And the combined focal length, and f ₂₃ is the second lens group (II) and the third lens group (II) when focused on infinity.
I) represents the combined focal length.

The conditional expressions (3) and (4) are both refraction of the second lens group (II) and the third lens group (III) for reducing the focusing movement amount and for not changing the focal length of the entire system even at the same magnification. It limits the force allocation.

When the lower limit of the conditional expression (3) or the upper limit of the conditional expression (4) is exceeded, the second lens group (II) and the third lens group (III) can be configured with relatively weak refractive power. Since the direction is closer to the so-called telephoto type at the same magnification side, it becomes difficult to correct distortion and coma. If the upper limit of conditional expression (3) or the lower limit of conditional expression (4) is exceeded, the refracting power of each lens group must be increased in order to maintain compactness, and it is easy to reduce the focusing movement amount. However, at the same magnification, the focal length of the entire system changes greatly, and it becomes difficult to correct coma and further it becomes difficult to correct the field curvature at infinity.

Next, examples of the present invention are shown in the table. In the table, f is the focal length, F NO. Is the F number, ri is the radius of curvature of the i-th lens surface from the object side, di is the i-th axial upper surface distance from the object side, and Ni is the i-th surface from the object side. The refractive index, νi, of the ith lens is the Abbe number of the ith lens from the object side. Furthermore, in the table, the subject distance indicates the subject distance from the lens.

In the embodiment of the present invention, the first lens group (I) has at least two positive lenses and one negative lens, and the second lens group (II) has at least one negative lens and one negative lens. Has three positive lenses, and the third lens group (III)
Has at least one positive lens and one negative lens.

[Brief description of drawings]

FIGS. 1, 2, 3, 4, 5, 6, and 7 show the lens arrangement in the infinity in-focus state of Embodiments 1, 2, 3, 4, 5, 6, and 7 of the present invention and the configuration thereof, respectively. It is sectional drawing which shows the moving direction of each lens group to a near distance by the arrow.
FIGS. 0, 11, 12, 13, and 14 are in the order of focusing at infinity (D = ∞), -0.5 times (β = -0.5), and -1.0 times (β = -1.0), respectively, in the above embodiment. FIG. 6 is an aberration diagram showing various aberrations of FIG. (I) ... First lens group, (II) ... Second lens group (III) ... Third lens group

Claims (2)

[Claims] 1. A first lens element having a positive refractive power in order from the object side.
It is composed of three groups of a lens group, a second lens group having a negative refracting power, and a third lens group having a positive refracting power. When focusing from an infinite distance to a close distance,
The first range so that the air distance between the first lens group and the second lens group and the air distance between the second lens group and the third lens group increase and decrease respectively at the maximum macro magnification. Telephoto macro lens characterized by giving different movements from the lens group to the third lens group and satisfying the following conditional expressions: 1.1 <f / f ₁ <1.7 0.15f <D ₂₃ <0.4f 0.35 < f / f ₁₂ <0.85 1.2 <f ₂₃ /f<5.0 where f is the focal length of the entire system at infinity focusing, f _{1 is} the focal length of the first lens group, D _{23 is} infinity On-axis air distance between the second lens group and the third lens group at the time of focusing, f ₁₂ ; infinity at infinity Composite focal length of the first lens group and the second lens group at the time of focusing, f ₂₃ ; at infinity Is a combined focal length of the second lens group and the third lens group at the time of focusing. 2. The first lens group has two positive lenses and one negative lens in order from the object side, and the second lens group has one negative lens and one positive lens, The telephoto macro lens according to claim 1, wherein the third lens group has one positive lens and one negative lens.