Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-03-22
2001-11-27
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
Reexamination Certificate
active
06324018
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention on relates to a compact zoom lens system which has a high vari-focal ratio.
b) Description of the Prior Art
To obtain a compact zoom lens system which has a high vari-focal ratio, it is effective to compose a lens system, in order from the object side, of a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power and a fourth lens unit having positive refractive power, and configure the lens system so as to change a magnification by moving the lens units.
As conventional examples of such a type of zoom lens system, there are known lens systems disclosed as fourth and sixth embodiments of Japanese Patent Kokai Publication No. Sho 58-78114, lens systems disclosed as first through fourth embodiments of Japanese Patent Kokai Publication No. Sho 58-224323, a lens system disclosed as a third embodiment of Japanese Patent Kokai Publication No. Sho 59-164517, lens systems disclosed as first through fifth embodiments of Japanese Patent Kokai Publication No. Sho 63-70819, a lens system disclosed as a second embodiment of Japanese Patent Kokai Publication No. Hei 3-29912, a lens system disclosed as a first embodiment of Japanese Patent Kokai Publication No. Hei 4-208911, a lens system disclosed as a second embodiment of Japanese Patent Kokai Publication No. Hei 5-173070, a lens system disclosed as a third embodiment of Japanese Patent Kokai Publication No. Hei 6-75167, a lens system disclosed as a first embodiment of Japanese Patent Kokai Publication No. Hei 8-43736, lens systems disclosed as first through third embodiments of Japanese Patent Kokai Publication No. Hei 6-337354, lens systems disclosed as first through eighth embodiments of U.S. Patent Publication No. 4256381 and a lens system disclosed as a fourth embodiment of U.S. Patent Publication No. 4299454.
However, the zoom lens systems quoted as the conventional examples have vari-focal ratios lower than 5 and cannot be said as zoom lens systems which have sufficiently high vari focal ratios, and it is difficult to further enhance the vari focal ratios of these zoom lens systems.
Furthermore, lens systems disclosed as first through fourth embodiments of Japanese Patent Kokai Publication No. Sho 62-270910 have high vari-focal ratios which are higher than 5, but a field angle of 64° at a wide position which is not large and it is difficult to further enlarge the field angle.
Furthermore, a zoom lens system disclosed by Japanese Patent Kokai Publication No. Hei 8-86963 has a high vari-focal ratio which is 6 or higher, but uses an aperture stop disposed in an airspace as narrow as 0.03 mm to 0.21 mm which is varied for changing a magnification and reserved between a final lens element of a second lens unit and a first lens element of a third lens unit. This airspace must be at least 0.4 mm in an actual product. In other words, the lens elements may be brought into contact with the aperture stop dependently on variations of parts. Even if the zoom lens system can be assembled into the product, the lens system is hardly assembled, thereby constituting a cause for an enhanced manufacturing cost.
Furthermore, a zoom lens system disclosed by Japanese Patent Kokai Publication No. Hei 9-5629 has a high vari-focal ratio which is not lower than 6, first through third embodiments of this conventional example cause remarkable variations of image surfaces by changing magnification and have optical performance which is not favorable. Moreover, a zoom lens system preferred as a fourth embodiment of this conventional example exhibits favorable optical performance at wide, standard and tele positions, but unbalances spherical aberration, curvature of field and distortion at an intermediate focal length which is located on a side of the tele position from the standard position and cannot correct these aberrations at the same time. In addition, a zoom lens system preferred as a fifth embodiment of this conventional example produces remarkable distortion on the side of the tele position.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a zoom lens system characterized in: that it has a fundamental composition wherein the zoom lens system comprises, in order from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power and a fourth lens unit having positive refractive power, a magnification at the wide position is changed to a magnification at the tele position by moving the first lens unit toward the object side, moving the second lens unit so as to widen an airspace reserved between the first lens unit and the second lens unit, moving the third lens unit so as to narrow an airspace reserved between the second lens unit and the third lens unit and moving the fourth lens unit so as to reserve an airspace between the third lens unit and the fourth lens unit at the tele position which is narrower than an airspace at the wide position, the second lens unit comprises, in order from the object side, a first lens component having negative refractive power, a second lens component having negative refractive power, a third lens component having positive refractive power and a fourth lens component having negative refractive power, a lens component having positive refractive power is disposed on the most object side and a negative lens component is disposed on the most image side in the third lens unit, the fourth lens unit comprises a front subunit and a rear subunit, the front subunit has positive refractive power and the rear subunit comprises a positive lens element and a negative lens element, an air lens having meniscus shape convex toward the image side is formed between the positive lens element and the negative lens element and the first lens unit and the second lens unit satisfy the conditions (1) mentioned below; and that the zoom lens system satisfies the following condition (2):
(1) 0.16<|f
2
|/f
1
<0.23
(2) 5<h×z/&Dgr;D
43
<27
Furthermore, the zoom lens system according to the present invention which has the fundamental composition described above is characterized by satisfying the following conditions (3) or (4) and (5):
(3) 0.09<D
4
/h<0.6
(4) 0.6<f
4F
/f
4
<1.8
(5) 4<f
4F
/D
4
<35
Furthermore, the zoom lens system according to the present invention which has the fundamental composition described above is characterized in that the front subunit of the fourth lens unit consists of a positive lens element which has a convex surface on the object side and positive refractive power.
Furthermore, the zoom lens system according to the present invention which has fundamental composition described above is characterized in that the front subunit of the fourth lens unit consists of a lens having positive refractive power which is convex toward the object side and a negative lens element which is disposed after the lens element having the positive refractive power at a location close thereto, and that surfaces of the lens element having the positive refractive power and the negative lens element which are opposed to each other have radii of curvature of the same sign.
Moreover, the zoom lens system according to the present invention which has the fundamental composition described above is characterized in that the third lens component of the second lens unit is a cemented lens component which consists of a positive lens element and a negative lens element.
Another object of the present invention is to provide a photographing apparatus wherein an optical path splitting means is disposed on the image side of the zoom lens system described above to split an optical path into a photographic optical path and an observing optical path.
REFERENCES:
patent: 4256381 (1981-03-01), Kreitzer
patent: 4299454 (1981-11-01), Betensky
patent: 58-078114 A (1983-05-01), None
patent: 58-224323 A (1983-12-01),
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
Sugarman Scott J.
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