Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-07-20
2001-02-27
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S683000
Reexamination Certificate
active
06195210
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compact and light-weight lens system which can be manufactured at a low cost and has high performance, and more specifically an image pickup lens system which is suited for use in lens shutter cameras and a camera which uses the image pickup lens system.
2. Description of the Prior Art
A zoom lens system which consists, in order from the object side, of a first lens unit having a positive refractive power and a second lens unit having a negative refractive power is conventionally known as a compact image pickup lens system such as a compact zoom lens system which can be manufactured at a low cost.
Lens systems disclosed by Japanese Patents Kokai Publication No. Hei 2-18511, No. Hei 5-224122, No. Hei 6-331899, No. Hei 7-253540 and No. Hei 8-334693 are known as conventional examples of image pickup lens system (zoom lens system) which has the composition described above.
Each of these conventional examples uses a first lens unit which is composed of three lens elements and a second lens unit which is composed of two lens elements, or each of the zoom lens systems consists as a whole of five lens elements. Four or all of the five lens elements are made of plastic materials to manufacture the zoom lens system at a low cost.
A lens system disclosed by Japanese Patent Kokai Publication No. Hei 5-113537 is also known as another conventional example. This conventional example also consists of five lens elements, and uses a plastic lens element having a relatively weak refractive power in a first lens unit and another plastic lens element in a second lens unit so that the lens system can be manufactured at a low cost while restricting focal lengths of the plastic lens elements and so on so as to reduce variations of imaging performance which are to be caused due to changes in environmental conditions such as temperature and humidity.
When plastic lens elements which have sufficiently strong refractive powers are used in a large number in a lens system as in the lens systems disclosed by Japanese Patent Kokai Publication No. Hei 2-18511, No. Hei 5-224122, No. Hei 6-331889, No. Hei 7-253540 or No. Hei 8-334693, the lens system has a defect that it allows its imaging performance to be varied due to changes of environmental conditions such as temperature and humidity. When the imaging performance is varied due to a humidity change in particular, a long time is required until the performance is stabilized, thereby making is difficult to preestimate how the imaging performance, for example an imaging location, will be changed and to correct a change of the imaging location by moving the lens elements. Imaging performance is remarkably degraded when plastic lens elements having sufficiently strong refractive powers are used in a large number as described above.
Furthermore, the lens system disclosed by Japanese Patent Kokai Publication No. Hei 5-113517 which uses only the two plastic lens elements out of the five lens elements cannot be manufactured at a sufficiently low cost.
Furthermore, the lens system disclosed by Japanese Patent Kokai Publication No. Hei 5-224122 uses a cemented plastic lens component in the first lens unit. However, a cemented plastic lens component which consists of two different kinds of plastic lens elements can hardly maintain a stable cemented condition since the plastic lens elements have high coefficients of expansion.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a compact and light-weight image pickup lens system which has favorable imaging performance to be varied little due to temperature changes or humidity changes and can be manufactured at a low cost as well as a camera which uses the image pickup lens system.
The image pickup lens system according to the present invention is a lens system characterized in that it comprises, in order from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, that the lens system is configured to change a magnification by varying an airspace reserved between the first lens unit and the second lens unit, that the first lens unit comprises, in order from the object side, a plastic lens element having a weak refractive power, a glass lens element having a negative refractive power and a glass lens element having a positive refractive power, and that the second lens unit comprises, in order from the object side, a plastic lens element having a weak refractive power and a plastic lens element having a negative refractive power.
Furthermore, the image pickup lens system according to the present invention which has a second composition is characterized in that it comprises at least a cemented lens component which is made of different glass materials and at least a lens element and that all cemented lens components are made of glass materials and lens elements are made of plastic materials.
REFERENCES:
patent: 5315440 (1994-05-01), Betensky
patent: 5386321 (1995-01-01), Kawamura
patent: 5786945 (1998-07-01), Aoki et al.
patent: 2-18511 (1990-01-01), None
patent: 5-113537 (1993-05-01), None
patent: 5-224122 (1993-09-01), None
patent: 6-331889 (1994-12-01), None
patent: 7-253540 (1995-10-01), None
patent: 8-334693 (1996-12-01), None
Epps Georgia
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
Schwartz Jordan M.
LandOfFree
Image pickup lens system and camera equipped with the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image pickup lens system and camera equipped with the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image pickup lens system and camera equipped with the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2567521