Optical: systems and elements – Lens – Multiple component lenses
Reexamination Certificate
2000-05-02
2001-01-30
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Multiple component lenses
C359S756000, C359S759000, C359S771000, C359S796000
Reexamination Certificate
active
06181488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photographic lens having a Gauss orthoscopic lens having six lens elements which are contained in two lens groups.
2. Description of the Related Art
This type of photographic lens has been known in, for example, Japanese Laid-Open Patent Publications (No.48-25528 and No.58-9117). Both of these applications have a two-lens group arrangement. The front lens group contains first, second and third lens elements, all of which are positive meniscus lenses having convex surfaces facing the object side. The second and third lens elements are cemented. The rear lens group contains the fourth, fifth and sixth lens elements. The fourth lens element is either positive meniscus lens or negative meniscus lens having a convex surface facing the image side. The fifth lens element having two concave surfaces, and the sixth lens elements having two convex surfaces, are cemented.
However, in the above-mentioned photographic lenses of the related art, aberration fluctuations, which occur due to a change of magnification when focusing is carried out to comply with a change of the object distances, are relatively large. Consequently, coma increases more when focusing is carried out on the object at a closer distance than when focusing is carried out on the object at a longer object distance, and a change of field curvature becomes excessive. In other words, the closer the object distance is, the more coma increases. Quality of image-forming performance worsens considerably especially when close-up photography is carried out at a magnification of around 0.5.
SUMMARY OF THE INVENTION
The object of the present invention, with the above-mentioned disadvantages taken into consideration, is to provide a photographic lens which can attain satisfactory image-forming performance even when close-up photography is carried out at a magnification of 0.5.
To achieve the above mentioned object there is provided a photographic lens comprising: a front lens group and a rear lens group that are arranged in order from the object side; wherein the front lens group comprises, in order from the object side, a first lens element which is a positive meniscus lens having a convex surface facing the object side, a second lens element which is a positive meniscus lens having a convex surface facing the object side, and a third lens element that is cemented to the second lens element, the third lens element being a negative meniscus lens having a convex surface facing the object side; wherein said rear lens group comprises, in order from the object side, a fourth lens element which is a positive meniscus lens having a convex surface facing the image side; a fifth lens element which is a negative meniscus lens having a concave surface on the object side; a sixth lens element that is cemented to the fifth lens element, the sixth lens element being a positive meniscus lens having a convex surface on the image side; and wherein the front lens group and the rear lens group are moved toward the object side so that the distance between the front and rear lens groups more increases when a focusing operation is performed on the object at a closer object distance than when a focusing operation is performed on the object at a longer object distance.
Under the condition that the traveling distance of the front lens group is designated as &Dgr;x1 and the traveling distance of the rear lens group is designated as &Dgr;x2, the ratio &Dgr;x2/&Dgr;x1 can be a constant value throughout a range defined by an in-focus state at infinity and by an in-focus state at the closest object distance. Furthermore, the ratio &Dgr;x2/&Dgr;X
1
preferably satisfies the following condition (1):
0.80
<&Dgr;x
2/
&Dgr;x
1<0.99 (1)
In addition, under the condition that the ratio &Dgr;x2/&Dgr;x1 is made variable, the ratio &Dgr;x2/&Dgr;x1 when an in-focus state is obtained at infinity is designated as XF, and the ratio &Dgr;x2/&Dgr;x1 when an in-focus state is obtained at the closest object distance is designated as XN, and the following conditions (2) is preferably satisfied:
0.0
<XN−XF<
0.1 (2)
Still further, under the condition that d6 is designated as the thickness of the fourth lens element, and f is the focal length of the entire lens system of the photographic lens, preferably the fourth lens is formed so that the following condition (3) is satisfied:
0.01
<d
6/
f<
0.05 (3)
The present disclosure relates to subject matter contained in Japanese Patent Application No.9-219894 (filed on July 31, 1997) which is expressly incorporated herein by reference in its entirety.
REFERENCES:
patent: 4784480 (1988-11-01), Yokota et al.
patent: 4943146 (1990-07-01), Iizuka
patent: 4991946 (1991-02-01), Goosey, Jr. et al.
patent: 5121257 (1992-06-01), Kanoshima
patent: 5930056 (1999-07-01), Ohashi
patent: 6002533 (1999-12-01), Yoneyama
patent: 51-39527 (1976-10-01), None
patent: 58-9117 (1983-01-01), None
patent: 51-34176 (1993-05-01), None
patent: 11-101939 (1999-04-01), None
Minefuji Nobutaka
Yoneyama Shuji
Asahi Kogaku Kogyo Kabushiki Kaisha
Epps Georgia
Greenblum & Bernstein P.L.C.
Spector David N.
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