Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-05-14
2001-10-23
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S676000, C359S683000
Reexamination Certificate
active
06307684
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a zoom lens system, and more specifically a zoom lens system in particular for compact cameras.
b) Description of the Prior Art
As zoom lens systems for compact cameras, there are conventionally known zoom lens systems including one which consists of two lens units, i.e., a first positive lens unit and a second negative lens unit, and is configured to change a focal length by varying an airspace reserved between the two lens units, and another zoom lens system which consists of three lens units, i.e., a first positive lens unit, a second positive lens unit and a third negative lens unit, and is configured to change a focal length by varying airspaces reserved among the lens units.
Out of these zoom lens systems, the zoom lens system which consists of the two lens units permits not only simplifying a lens barrel structure and a drive mechanism but also reducing a number of lens components to be used, thereby being more advantageous for lowering a manufacturing cost than the zoom lens system which consists of the three lens units. On the other hand, the zoom lens system which consists of the three lens units is more excellent in that it can be configured to have a zoom ratio as high as possible and be compact as a whole.
Lens system disclosed by Japanese Patents Kokai Publication No. Hei 4-260016 and Kokai Publication No. Hei 5-188296 are known as conventional examples of zoom lens system which is configured to use lens elements in a minimum number to reduce a manufacturing cost. Out of these conventional examples, the former adopts a first positive lens unit which consists a positive lens component, a second lens unit which consists of a negative lens component and a positive lens component, and a third lens unit which consists of a negative lens component. The latter zoom lens system adopts a first lens unit which consists of a negative lens component and a positive lens component, a second lens unit which consists of a negative lens component and a positive lens component, and a third lens unit which consists of a negative lens component.
To configure the zoom lens system which consists of the first positive lens unit, the second positive lens unit and the third negative lens unit so as to have a higher zoom ratio and more compact design, it is sufficient to strengthen a refractive power of each of the lens components by shortening a radius of curvature on each lens surface. In such a case, however, aberrations are produced in larger amounts and remarkably varied during zooming. To reduce variations of aberrations during zooming so as to obtain aberrations favorably corrected in an entire zooming region and a sufficiently high vari-focal ratio, each of the lens units must be composed of a larger number of lens components and the zoom lens system is inevitably enlarged as a whole. Furthermore, it becomes more difficult to manufacture the zoom lens system at a low cost as it is composed of a larger number of lens components. When a refractive power of each of the lens component is weakened to reduce variations of aberrations during a change of a magnification, the lens units must be moved for longer distances for changing a magnification, thereby making it impossible to configure the zoom lens system compact.
Furthermore, the zoom lens system which consists of the three lens units described above produces positive spherical aberration and aggravates longitudinal chromatic aberration at a tele position since the third lens unit has a strong negative refractive power. Furthermore, the zoom lens system produces positive distortion in a larger amount and aggravates coma at a wide position.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a zoom lens system for compact cameras which has a high zoom ratio and high optical performance.
The zoom lens system according to the present invention comprises, in order from the object side, a first positive lens unit, a second positive lens unit and a third negative lens unit: the first lens unit comprising a positive lens component which is disposed on the object side, and a negative meniscus lens component which is disposed on the image side of the positive lens component and has a concave surface on the image side. The zoom lens system is configured to change a magnification from a wide position to a tele position by varying an airspace reserved between the first lens unit and the second lens unit as well as an airspace reserved between the second lens unit and the third lens unit.
REFERENCES:
patent: 5325235 (1994-06-01), Takashima et al.
patent: 5715096 (1998-02-01), Meyers
patent: 5726810 (1998-03-01), Meyers
patent: 5731914 (1998-03-01), Meyers
patent: 5751485 (1998-05-01), Suzuki
patent: 5777799 (1998-07-01), Miyauchi
patent: 5825556 (1998-10-01), Meyers
patent: 5831772 (1998-11-01), Nishio et al.
patent: 6025960 (2000-02-01), Morooka
patent: 6064531 (2000-05-01), Ishii et al.
patent: 4-260016 (1992-09-01), None
patent: 5-188296 (1993-07-01), None
Epps Georgia
Olympus Optical Co,. Ltd.
Pillsbury Madison & Sutro LLP
Spector David N.
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