Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-04-23
2003-04-22
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S672000, C359S676000, C359S691000, C359S795000, C359S707000
Reexamination Certificate
active
06552857
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a soft-focus lens system, and in particular, relates thereto in which a soft-focus photographing mode can be switched to a normal photographing mode without soft-focus effects or vice versa, and which can be used in a single lens reflex (SLR) camera.
2. Description of the Prior Art
A soft-focus lens system of the above type has been disclosed in, e.g., Japanese Unexamined Patent Publication (hereinafter, JUPP) No. 8-86957. In the lens system of this publication, when the normal photographing mode is switched to the soft-focus photographing mode or vice versa, the focal point and the focal length are inevitably varied. If this occurs before and after the switching of the photographing modes, a focusing operation has to be done again. Furthermore, if an attempt is made to automatically correct the varied focal point and focal length by a predetermined mechanism, the structure of the lens system has to become complicated.
Still further, in a lens system which has been disclosed in, e.g., JUPP No. 8-248310, the change of the focal length caused by the switching of the above photographing modes is cancelled by moving another lens system. However, such an arrangement is a type of a zoom mechanism, which also makes the structure of the lens system complicated.
In the above conventional soft-focus lens systems, focusing is performed by advancing the most object-side lens group, or by advancing the entire lens system. As a result, the overall length of the lens system becomes longer. Moreover, the weight of a lens group(s) to perform focusing is heavy, so that it is difficult for a user to easily handle and carry the camera with him/her. Furthermore, it is not suitable to incorporate an automatic focusing (AF) function into such a lens system.
In addition to the above, it has been known that a soft-focus lens system, which (i) can form a clear image in the normal photographing mode, and (ii) can generate uniform flare from the center of the image filed to the periphery thereof in the soft-focus photographing mode, has utilized spherical aberration occurred in lens elements. However, there are requirements that options on the effects of soft-focusing, in addition to the effects of soft-focusing obtained by spherical aberration, be increased in order to widen photographic expressions.
SUMMARY OF THE INVENTION
The present invention is to provide a soft-focus lens system which (i) can maintain the focal point and the focal length before and after the switching of the soft-focus photographing mode to a normal photographing mode or vice versa, and which (ii) can dispense with a complicated movement of the lens groups, (iii) can avoid increasing the weight of a lens group(s) to perform focusing, and (iv) can increase options on the effects of soft-focusing in order to widen photographic expressions by utilizing not only spherical aberration but also filed curvature.
As a first aspect of the present invention, there is provided a soft-focus lens system including a positive master lens group (hereinafter, master lens group) and a negative soft-focus lens group (hereinafter soft-focus lens group). The soft-focus lens group includes at least two moveable sub lens groups, i.e., a positive sub lens group and a negative sub lens group, which are independently moveable with respect to the master lens group. The positive sub lens group and the negative sub lens group are moved to set the normal photographing mode or the soft-focus photographing mode in which larger spherical aberration is occurred than in the normal photographing mode. Furthermore, each of the sub lens groups is arranged to move with respect to the master lens group and the other of the sub lens groups so that the focal point and the focal length are not substantially varied before and after the switching of the soft-focus photographing mode to the normal photographing mode or vice versa.
Due to the following reasons, the soft-focus lens group has negative power:
(1) the normal photographing mode is switched to the soft-focus photographing mode or vice versa by changing the distance between the positive sub lens group and the negative sub lens group;
(2) under this arrangement, if the soft-focus lens group has positive power, the changes of the focal point and the focal length are corrected by moving the positive soft-focus lens group toward the image by a predetermined distance;
(3) however, moving the positive soft-focus lens group by a predetermined distance toward the image makes the diameter of a bundle of light rays passing therethrough smaller, thereby spherical aberration becomes smaller;
(4) in other words, such a decrease of spherical aberration is equivalent to canceling the effects of soft-focusing;
(5) on the other hand, if an attempt is made to further increase the positive power of the positive soft-focus lens group so that the change of the focal point due to the effects of soft-focusing is corrected by moving the positive soft-focus lens group by a distance shorter than the above predetermined distance, the positive power of the master lens group becomes weaker; and
(6) as a result, the second principal point moves toward the image, so that the overall length of the lens system becomes longer.
Since there is freedom on the positional relation between the master lens group and the soft-focus lens group, the arrangement thereof in the first aspect of the present invention can be made as follows:
(a)the master lens group and the soft-focus lens group are arranged in this order from the object;
(b) a diaphragm is provided in the master lens group; and
(c) the soft-focus lens group includes the positive sub lens group and the negative sub lens group, in this order from the object, which are constituted by a positive single lens element and a negative single lens element so that an air lens, having a shape of a meniscus lens element with the concave surface facing toward the diaphragm, is formed between the positive single lens element and the negative single lens element.
According to a second aspect of the present invention, a positive lens group to exclusively perform focusing (hereinafter, focusing lens group) to obtain an in-focus state of the object is provided between the master lens group and the soft-focus lens group. In other words, the soft-focus lens system according to the second aspect of the present invention includes the master lens group, the positive focusing lens group (hereinafter, focusing lens group) and the soft-focus lens group, in this order from the object. The arrangement of the soft-focus lens group and the function thereof are the same as the first aspect of the present invention. Each of the sub lens groups of the soft-focus lens group is arranged to move with respect to the master lens group, the focusing lens group and the other of the sub lens groups so that the focal point and the focal length are not substantially varied before and after the switching of the soft-focus photographing mode to the normal photographing mode or vice versa. In the second aspect of the present invention, the master lens group is made constantly immoveable, and the focusing lens group exclusively functions as a lens group to perform focusing to obtain an in-focus state of the object regardless of the positions of the sub lens groups of the soft-focus lens group.
It is practical to provide the diaphragm in the focusing lens group. Similar to the first aspect of the present invention, the positive sub lens group and the negative sub lens group of the soft-focus lens group are constituted by a positive single lens element and a negative single lens element so that an air lens, having a shape of a meniscus lens element with the concave surface facing toward the diaphragm, is formed between these positive and negative lens elements.
Here, a third aspect of the present invention will be discussed. The third aspect of the present invention is devised based on the requirements that the effects of soft-focusing be more beautifully refin
Greenblum & Bernstein P.L.C.
Hasan M.
PENTAX Corporation
LandOfFree
Soft-focus lens system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Soft-focus lens system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Soft-focus lens system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3084233