Optical: systems and elements – Lens – Multiple component lenses
Reexamination Certificate
2001-03-14
2002-08-20
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Lens
Multiple component lenses
C359S754000, C359S756000
Reexamination Certificate
active
06437926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image capture lens and an image capture apparatus which are used for reading various kinds of images.
2. Description of the Related Art
An image capture apparatus, in which an image of an original such as a negative film or positive film is formed on a solid state image sensor such as a charge-coupled device (CCD) serving as a light-receiving device through a image capture optical system, and then image information is read, has been developed. With the increase of high density in the light-receiving device, high resolution of an image capture lens employed in the optical system of the image capture apparatus is in demand in recent years. Particularly, with regard to the image capture lens which is utilized in the image capture apparatus in which color images are read with one CCD, for example, achromatization needs to be performed preferably in order that imaging points of images composed of each color: red (R), green (G) and blue (B) correspond to each other on the light-receiving surface of the CCD, and desirably resolution levels of each color on the device are maintained. Specifically, the image capture lens is required to exhibit imaging performance such that axial chromatic aberration and chromatic aberration of magnification of each RGB color are small, and images from the center to peripheries are formed on a plane substantially vertical to the optical axis. When the image capture lens has such imaging performance, high-contrast images with each RGB color can be obtained.
However, there exists a problem such that, if axial chromatic aberration is not corrected enough in the image capture lens, imaging points of each RGB color do not correspond to each other. Therefore, even though individual resolution of each RGB color is in high contrast, variations in contrast of each RGB color occur depending on the imaging point. To correct such variations in contrast, a mechanism which focuses each color individually or a method such that an image plane is shifted in accordance with the magnitude of chromatic aberration is necessary.
When ‘f’ and &bgr;(&bgr;<0) represent focus length and imaging magnification of a lens, the magnitude of axial chromatic aberration &Dgr;S is expressed by &Dgr;S∝(1−&bgr;)
2
*f, which denotes that as the focal length f becomes longer or the absolute value |&bgr;| of the imaging magnification becomes larger, the amount of axial chromatic aberration occurred increases. This is noticeable in a lens made of a material with no anomalous dispersion. In such a lens, axial chromatic aberration is not sufficiently corrected. Particularly, it is difficult to obtain high contrast simultaneously between each RGB color in a magnification range. Thus, when such high-level axial chromatic aberration is subjected to correct in the image capture lens, use of a lens material with high anomalous dispersion is effective. In that case, as the anomalous dispersion is larger, the effect of correction is larger. Further, as the refractive power is larger, the effect of correction is larger. However, if the refractive power is made too large, the magnitude of various kinds of aberrations becomes larger resulting in deterioration of image quality. Accordingly, when the material with large anomalous dispersion is used for the ‘i’th lens element in the image capture lens, for example, desirably by giving a moderate value for &Sgr;&phgr;
i
*&dgr;&thgr;
i
which is the sum of the products of the refractive power &phgr;
1
(&phgr;
i
=1/f
i
) and the anomalous dispersion &dgr;&thgr;
i
of the lens elements made of the material, axial chromatic aberration is made smaller and other aberrations are preferably corrected.
Although many image capture lenses in which achromatization is utilized have been proposed heretofore, magnification used in most of the conventional capture lenses is reducing imaging magnification such as −0.1× to −0.2×, thus large axial chromatic aberration which occurs in magnifying images is difficult to correct. Therefore, the conventional image capture lenses are not adequate for capturing images with scaling them up or down crossing over the magnification of the actual size, for example. For example, if the conventional image capture lenses are used in the magnification range of −0.6× to −1.6×, it is difficult to form preferable images by scaling them up in particular.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above problems. It is an object of the invention to provide an image capture lens and an image capture apparatus in which various kinds of aberrations are corrected and optical performance suitable for capturing images is obtained.
In the image capture lens of the first aspect of the invention, successively from an object side provided are a first lens group including a negative meniscus lens; a second lens group including a positive lens directing its convex to the object side; a third lens group including a first cemented lens composed of a bi-convex positive lens and a bi-concave negative lens, the first cemented lens having positive refractive power and directing its convex to the object side; a fourth lens group including a second cemented lens composed of a bi-concave negative lens and a bi-convex positive lens, the second cemented lens having negative refractive power and directing its convex to an image side; a fifth lens group including a positive lens directing its convex to the image side; and a sixth lens group including a negative lens directing its concave to the object side.
The image capture apparatus of the first aspect of the invention reads images through the image capture lens of the first aspect of the invention.
In the image capture lens of the first aspect of the invention, desirably expressions 65<&ngr;
3
, 0.015<&dgr;&thgr;
3
, 65<&ngr;
6
and 0.015<&dgr;&thgr;
6
are satisfied when the &ngr;
3
and the &dgr;&thgr;
3
; represent Abbe number for a wavelength of d-line and anomalous dispersion of the positive lens in the third lens group, and the &ngr;
6
and the &dgr;&thgr;
6
represent Abbe number for the wavelength of d-line and anomalous dispersion of the positive lens in the fourth lens group.
In the image capture lens of the first aspect of the invention, desirably expressions 0.09<(&phgr;
3
*&dgr;&thgr;
3
+&phgr;
6
*&dgr;&thgr;
6
)/&phgr;
T
<0.15, 0.75<(n
3
*&ngr;
4
)/(n
4
*&ngr;
3
)<1.10 and −13.0<&phgr;
T
2
/(&phgr;
3,4
*&phgr;
5,6
)<−0.3 are satisfied when the
3
and the &dgr;&thgr;
3
represent refractive power and anomalous dispersion of the positive lens in the third lens group, respectively, the &phgr;
6
and the &dgr;&thgr;
6
represent refractive power and anomalous dispersion of the positive lens in the fourth lens group, respectively, the &ngr;
3
and the n
3
represent Abbe number and refractive index for the wavelength of d-line of the positive lens in the third lens group, respectively, the &ngr;
4
and the n
4
represent Abbe number and refractive index for the wavelength of d-line of the negative lens in the third lens group, respectively, and the &phgr;
3,4
represents refractive power of the entire cemented lens in the third lens group, &phgr;
5,6
represents the refractive power of the entire cemented lens in the fourth lens group and the &phgr;
T
represents refractive power of an entire lens system including all the lens groups.
In the image capture lens of the second aspect of the invention, successively from an object side provided are a first lens group including a negative meniscus lens; a second lens group including a positive lens directing its convex to the object side; a third lens group including a first cemented lens composed of a bi-convex positive lens and a bi-concave negative lens, the first cemented lens having positive refractive power and directing its convex to an object side; a fourth lens group including a second cemented le
Dang Hung Xuan
Frommer & Lawrence & Haug LLP
Ryan Matthew K.
LandOfFree
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