Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-07-24
2004-08-03
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S683000
Reexamination Certificate
active
06771433
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens, a variable magnification group, a camera unit having a photographic lens using such a zoom lens, a digital camera, a video camera, and a portable information terminal unit as an information equipment having a digital image photographing function.
2. Prior Art
The digital camera market is being extraordinarily expanded. Photographing of digital image is extended not only to a digital camera but also to a portable information terminal unit of portable telephone, and demands of users for digital camera are multilaterally branched. Among them, high image quality and miniaturization are always desired by the users and are given much weight among the various desired items. For this reason, high performance and miniaturization are also required to be compatible in a zoom lens used as a photographic lens.
In view of miniaturization, first of all, it is require to reduce the total length of lens (the distance from the most object side lens surface to an image surface). Furthermore, in a camera unit of so called “collapsible mount style” that is contemplated for compactness at the time of receiving a lens, it is important to reducing the thickness of each group, which moves at the time of zooming, in the direction of optical axis in order to reduce the dimension at the time of reception.
Although various types are considered for the zoom lens for digital camera, there is a type which is appropriate for miniaturization, which comprises a first group with a negative focal length, a second group with a positive focal length, a third group with a positive focal length in turn from the object side, and an iris provided in the object side of the second group to move integral with the second group, wherein the second group monotonously moves from the object side to the image side at the time of variation of magnification from the short focus end to the long focus end, and the first group moves to correct the variation in position of an image surface accompanying the variation of magnification.
For example, although Japanese Patent Publication No. Hei. 10(1998)-039214 discloses all of the basic construction before everything else among those of which proposed the zoom lenses of the above type, it is not always sufficient in the aspect of miniaturization. Although a zoom lens improved over the above type and advanced in miniaturization is disclosed in Japanese Patent Publication No. Hei. 11(1999)-287953, the miniaturization is not sufficient and also aberration correction cannot to be said as sufficient because only one aspherical surface is provided in the second group. Although Japanese Patent Publication No. 2000-089110 discloses a zoom lens which is contemplated for good correction of aberration using the two aspherical surfaces in the second group as its embodiment 3, it is not always advantageous in miniaturization because the thickness of second group is large.
Also, because the examples of prior art which are disclosed in these publications are not appropriate in the construction of each group, in particular the second group, sufficient aberration correction do not take place and do not have a performance which is able to cope with an image sensing device of 2,000,000 to 4,000,000 pixels.
SUMMARY OF THE INVENTION
Considering the above problems, it is an object of the present invention to contemplate the miniaturization of zoom lens used for photographing a digital image while maintaining high performance thereof.
In addition, it is an object of the present invention to provide a zoom lens and camera having a definition corresponding to an image sensing device of 2,000,000 to 4,000,000 pixels.
Furthermore, because it is important to minimize a lens diameter (maximum light effective diameter) in order to avoid the large-sizing of lens barrel formed from a plurality of stages in the case of zoom lens used in the camera of so called collapsible mount style, it is an object of the present invention to provide a zoom lens, a camera and a portable information terminal unit which are sufficiently compact while having high performance and of which the lens diameter (maximum light effective diameter) of the first group amongst others is small.
In the zoom lens consisting of three groups of negative, positive and positive as in the present invention, in general, when magnification is varied from short focus end to long focus end, the second group monotonously moves from the image side to the object side and the first group moves to correct the variation in position of an image surface accompanying the variation of magnification. The second group takes charge of most of variation of magnification function and the third group is provided mainly to keep exit pupil away from the image surface.
In order to realize a zoom lens of high definition, of which various aberrations are small, the variation of aberration due to variation of magnification should be restrained to be small, and in particular a variable magnification group which performs substantial variation of magnification, i.e., the second variable magnification group which is the main variable magnification group is needed to be excellently aberration-corrected in the total range of variation of magnification. For the excellent correction of aberration of the second group, basically it is considered to increase the constituent number of second group but the increase of constituent number will increase the thickness of second group in the direction of optical axis, whereby it will be impossible to attain sufficient miniaturization and furthermore the increase of cost will be caused.
Although second groups consisting of not more than four lenses are known: that consisting of three lenses: a positive lens, a negative lens, and a positive lens in tarn from the object side; that consisting four lenses: a positive lens, a positive lens, a negative lens, and a positive lens in turn from the object side; and that consisting of four lenses: a positive lens, a negative lens, a negative lens, and a positive lens in turn from the object side, the present invention realizes a second group having a aberration correcting capability over them.
That is, in the present invention, a zoom lens comprising the first group with a negative focal length, a second group with a positive focal length, and a third group with a positive focal length in turn from the object side, and including an iris provided in the object side of said second group to be moved integrally with the second group, in which at the time of variation of magnification from short focus end to long focus end, the second group monotonously moves from the image side to the object side and the first group moves to correct the variation in position of image surface accompanying the variation of magnification, wherein the second group consists of four lenses: a positive lens, a negative lens, a positive lens and a positive lens in turn from the object side.
Due to the relationship that an aperture iris is located in the object side of second group, in the second group, as a lens of image side is more remote from the aperture iris, its abaxial light passes a place which is more deviated from the optical axis, thereby deeply taking part in correction of abaxial aberration. Although the second group has a symmetrical arrangement having two positive magnifications each being provided on each side of a negative magnification, the positive magnification of image side which deeply takes part in correction of abaxial aberration is divided in two lenses, whereby degree of freedom is increased and it becomes possible to excellently correct the abaxial aberration.
In order to execute more sufficient correction of aberration, it is preferable to satisfy the following conditional relationship.
0.9<(
L
PN
/Y
′)<1.4
Wherein, L
PN
is the distance from the apex of object side surface of the most object side positive lens of the second group to the apex of image side surface of negative lens, which is the seco
Choi William
Dickstein , Shapiro, Morin & Oshinsky, LLP
Epps Georgia
Ricoh & Company, Ltd.
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