Photography – Having variable focal length of camera objective – Having focus operation
Reexamination Certificate
1999-02-17
2001-06-12
Perkey, W. B. (Department: 2851)
Photography
Having variable focal length of camera objective
Having focus operation
C359S686000
Reexamination Certificate
active
06246833
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photographic lenses and photographing apparatus and, more particularly, to a photographic lens capable of focusing on an object in a wide range from infinity to as short distances with life-size magnification and a photographing apparatus having the photographic lens.
2. Description of Related Art
For a camera for photography, such as video camera or the still video camera, there has been developed a photographic lens that aims mainly at photographing close objects, or what is called the “macro” or “micro” lens (hereinafter generally referred to as the “macro” lens).
The macro lens is so designed that high optical performance is obtained when photographing an object especially at a closer distance than with other types of photographic lenses, such as the standard lens and telephoto lens in a normal image distance setting. Again, the macro lens is, in many cases, used even when shooting not only a close object but also an object in a wide range of distances from infinity to the minimum.
In general, with the macro lens, if it is intended to extend the focusing range toward shorter object distances (or the range of magnifications toward larger image sizes), aberrations vary with focusing to an even wider extent, increasing greatly particularly in closeup photography or at high reproduction ratios, and, therefore, become difficult to correct well in this region. So, as can be seen in Japanese Laid-Open Patent Application No. Sho 63-179308, a focusing method is proposed which uses at least two lens units arranged to axially move independently of each other, or utilizes the so-called “floating” technique. The of aberrations variation with focusing is thus minimized.
In the meantime, in Japanese Patent No. 2,556,986 and Japanese Laid-Open Patent Application No. Hei 4-110811, there has been proposed a photographic lens comprising, in order from an object side to an image side, a positive lens unit, a negative lens unit, a positive lens unit and a negative lens unit, wherein during focusing to closer object distances, the first and fourth lens units remain stationary relative to the image plane, the second lens unit moves toward the image side and the third lens unit moves toward the object side.
Also, in Japanese Laid-Open Patent Application No. Hei 8-76012, for the photographic lens comprising, in order from an object side to an image side, a positive lens unit, a negative lens unit, a positive lens unit and a negative lens unit, another method is proposed that, during focusing to closer object distances, the first lens unit remains stationary relative to the image plane and the second, third and fourth lens units move.
However, most of the macro lenses including that disclosed in Japanese Laid-Open Patent Application No. Sho 63-179308 employ the method of bodily moving the whole lens system forward. If a lens unit of a large size is selected to use in focusing, the driving torque of an electrically-operated control means such as a motor has to increase. In the auto-focus camera that moves the focusing lens unit by the electric motor, therefore, high-speed focusing becomes difficult to carry out.
The arrangements disclosed in the above Japanese Patent No. 2,556,986 and Japanese Laid-Open Patent Application No. Hei 4-110811, because of moving the second and third lens units of lighter weight than that of the first lens unit, are advantageous for automatic focusing. However, to assure maintenance of good stability of image quality over the entire extended focusing range from the setting for infinity to a setting for about life-size magnification, further improvements of the aberration correction must be sought for.
The arrangement disclosed in the above Japanese Laid-Open Patent Application No. Hei 8-76012 has not realized the capability of focusing up to an object of life-size magnification.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a photographic lens capable of focusing over a wide range of object distances from infinity to so close a distance that the image is magnified to life-size or thereabout, while still maintaining good stability of image quality over the entire focusing range.
To attain the above object, in accordance with an aspect of the invention, there is provided a photographic lens, which comprises, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of negative refractive power, wherein, during focusing from an infinitely distant object to a minimum-distance object, the first lens unit remains stationary, the second lens unit moves toward the image side, the third lens unit moves toward the object side and the fourth lens unit moves in such a way as to include a locus convex toward the object side.
In accordance with another aspect of the invention, there is provided a photographic lens, which comprises, in order from an object side to an image side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power, and a fourth lens unit of positive refractive power, wherein, during focusing from an infinitely distant object to a minimum-distance object, the first lens unit and the fourth lens unit remain stationary, the second lens unit moves toward the image side and the third lens unit moves toward the object side, and wherein, during a maximum photographic magnification, the separation between the second lens unit and the third lens unit is made a minimum, and the photographic lens satisfies the following conditions:
0.45
<f
1
/f<
0.6
−0.48
<f
2
/f<−
0.29
0.76
<f
3/
f<
1.85,
where f is the focal length of the photographic lens, and f1 is the focal length of the i-th lens unit.
Further, in accordance with a further aspect of the invention, there is provided a photographing apparatus, which comprises the photographic lens described above.
REFERENCES:
patent: 3507555 (1970-04-01), Isshiki
patent: 4906079 (1990-03-01), Mihara et al.
patent: 63-179308 (1988-07-01), None
patent: 4-110811 (1992-04-01), None
patent: 8-76012 (1996-03-01), None
patent: 2556986 (1996-09-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Perkey W. B.
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