Optical: systems and elements – Lens – Multiple component lenses
Reexamination Certificate
2002-11-26
2004-06-08
Spector, David N. (Department: 2873)
Optical: systems and elements
Lens
Multiple component lenses
C359S785000
Reexamination Certificate
active
06747817
ABSTRACT:
The application claims benefit of Japanese Application No. 2001-361096 filed in Japan on Nov. 27, 2001, the contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
The present invention relates to a macro lens and a camera comprising the same. The present invention is particularly suitable for silver-halide or digital cameras. More specifically, the present invention is directed to a macro lens suitable for use as an interchangeable lens applicable to silver-halide or digital single-lens reflex cameras.
So far, many macro lenses have been proposed as interchangeable lenses for single-lens reflex cameras or digital single-lens reflex cameras.
For focusing macro lenses, floating techniques involving the movement of a plurality of groups have been used, because of a large fluctuation of spherical aberrations between at infinity and at close range.
Conventional macro lenses, for the most part, give weight to designs having a magnification of about {fraction (1/10)} while they are well balanced at infinity and at close range, and so their phototaking performance at infinity is inferior to that of general lens systems that are in no sense any macro lens systems.
Many macro lenses have large fluctuations of spherical aberrations and field curvature at infinity to close range upon focusing, and so such aberrations are reduced by means of floating.
With large-aperture macro lenses, however, it is difficult to control these fluctuations, and so field curvature and coma in particular become noticeable in short range regions.
SUMMARY OF THE INVENTION
In view of such problems with the prior art as explained above, one object of the present invention is to provide a fast macro lens that is well corrected for aberrations even upon close-range shooting, and a camera comprising the same.
Another object of the present invention is to provide a large-aperture macro lens that has reduced aberration fluctuations at every range from infinity to close range and an F-number of about 1.8.
Yet another object of the present invention is to provide a macro lens best suited for half film size and an image circle nearly half the diagonally 135-long format.
According to the first aspect of the present invention, these objects are achievable by the provision of a macro lens, characterized by comprising, in order from its object side, a first lens group having positive power and a second lens group having positive power, wherein in the first lens group a negative meniscus lens component concave on its object side is located nearest to the object side of the first lens group, and upon focusing from an object point at infinity to the closest object point, the first lens group and the second lens group move independently toward the object side of the macro lens while the spacing between them varies.
According to the second aspect of the present invention, there is provided a macro lens characterized by comprising, in order from an object side thereof, a first lens group having positive power, a second lens group having negative power and a third lens group having positive power, wherein in the first lens group a negative meniscus lens component concave on its object side is located nearest to the object side of the first lens group, and upon focusing from an object point at infinity to the closest object point, the lens groups move independently toward the object side of the macro lens while a spacing between adjacent lens group varies.
In what follows, why the aforesaid arrangements are used, and how they work will be explained.
The macro lens of the present invention may be used on cameras in general. In particular, this macro lens is best suited for use on a single-lens reflex camera (irrespective of whether or not lens replacement is needed), which must take a back focus enough to mount therein an observation optical path-dividing mechanism. The macro lens of the present invention is also applicable to just only silver-halide silver cameras but also to other cameras using electronic image pickup devices such as solid-state image pickup devices or CCDs.
Comprising two positive lens groups, the micro lens of the present invention makes correction for aberrations upon focused at close range by means of the floating action ensuing from independent movement of them.
For lens replacement, a macro lens for single-lens reflex cameras must take a given back focus length. Although the lens of the present invention is a medium-telephoto lens system having a view angle of 2&ohgr;≈about 24°, its focal length with respect the view angle reduces by nearly half that of the 135 format. With the lens system according to the specification of the present invention, it is thus not easy to make sure of the back focus.
To ensure this back focus, the first lens component located nearest to the object side of the first lens group having positive power must be formed of a negative lens component. To bring the principal point at a position in the rear of the lens system and on the image side of the lens system, the first lens component should preferably be defined by a negative meniscus lens component concave on its object side. With this arrangement, it is possible to take an adequate back focus length and, hence, make sure of space large enough to receive a quick-return mirror.
Thus, the first micro lens of the present invention has the structure comprising, in order from an object side thereof, a first lens group having positive power and a second lens group having positive power, wherein in the first lens group a negative meniscus lens component concave on an object side thereof is located nearest to the object side of the first lens group, and upon focusing from an object point at infinity to the closest object point, the first lens group and the second lens group move independently toward the object side of the macro lens while the spacing between them varies.
Alternatively, the second macro lens of the present invention has the structure comprising, in order from an object side thereof, a first lens group having positive power, a second lens group having negative power and a third lens group having positive power, wherein in the first lens group a negative meniscus lens component concave on an object side thereof is located nearest to an object side of the first lens group, and upon focusing from an object point at infinity to the closest object point, the lens groups move independently toward the object side of the macro lens while the spacing between adjacent lens group varies.
In this embodiment of the present invention, the three lens groups are positioned in a nearly symmetric power profile of +-+, and aberrations upon focusing at close range are corrected by the floating action ensuing from their independent movement.
To hold back aberration fluctuations every range from infinity to close range while close-range performance is improved, floating should preferably be carried out by the movement of the three lens groups of +-+ power profile. With this arrangement, fluctuations of spherical aberrations and coma with focusing can be reduced as much as possible, and field curvature fluctuations can be easily corrected as well.
It is here understood that the two-group arrangement is overwhelmingly favorable for the associated lens barrel structure, and so can be much more reduced in terms of performance variations by fabrication errors than the three-group arrangement.
A stop should preferably be inserted in the first lens group in the case of the two-group arrangement, and in the second lens group in the case of the three-group arrangement.
Where the height of a marginal ray minimizes is in the first lens group in the case of the two-group arrangement, and in the second lens group in the case of the three-group arrangement; it is most preferable to locate the stop at that position, at which the stop can be made more compact because its diameter can become short. At that position, the marginal ray minimizes in height, taking the form of a substantially afocal ray, so that even w
Olympus Corporation
Pillsbury & Winthrop LLP
Spector David N.
LandOfFree
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