This application is based on Japanese Patent Applications Nos. 2000-111913 and 2000-368338, filed on Apr. 7, 2000 and Dec. 4, 2000, respectively, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical or taking lens device. More specifically, the present invention relates to an optical or taking lens device that optically takes in an image of a subject through an optical system and then outputs the image as an electrical signal by means of an image sensor. For example, an optical or taking lens device is used as a main component of a digital still camera, a digital video camera, or a camera that is incorporated in, or externally fitted, to a device such as a digital video unit, a personal computer, a mobile computer, a portable telephone, or a personal digital assistant (PDA). The present invention relates particularly to an optical or taking lens device provided with a high-zoom-ratio, high-performance zoom lens system.
2. Description of Prior Art
Conventionally, the majority of high-zoom-ratio zoom lenses for digital cameras are of the type comprising, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a positive optical power (for example, Japanese Patent Application Laid-Open No. H4-296809). This is because a positive-negative-positive-positive configuration excels in compactness.
On the other hand, as zoom lenses aiming for higher zoom ratios are known zoom lenses of the type comprising, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, a fourth lens unit having a positive optical power, and a fifth lens unit having a positive optical power (for example, Japanese Patent Application Laid-Open No. H6-317751). This positive-negative-positive-positive-positive configuration is also known as a configuration used in interchangeable lenses for single-lens reflex cameras (for example, Japanese Patent Application Laid-Open No. H7-311340).
However, the zoom lens proposed in Japanese Patent Application Laid-Open No. H6-317751 mentioned above keeps its first lens unit stationary during zooming, and is therefore unfit for further improvement for higher performance necessitated by the trend toward higher zoom ratios and smaller image-sensor pixel pitches. On the other hand, the zoom lens proposed in Japanese Patent Application Laid-Open No. H7-311340, mentioned above, is designed for single-lens reflex cameras, and is therefore unfit for digital or video cameras. In particular, the directions in which this zoom lens moves its second to fourth lens units are also unfit for such applications and it is impossible to achieve a high zoom ratio or obtain satisfactory aberration characteristics. The positive-negative-positive-positive configuration mentioned first has been used in the majority of conventional high-zoom-ratio zoom lenses, but is still susceptible to optimization in terms of how to move individual lens units and how to distribute different optical powers.
An object of the present invention is to provide an optical or taking lens device with a compact, high-zoom-ratio, high-performance zoom lens system that, despite comprising as few as four lens units, i.e., a positive lens unit, a negative lens unit, a positive lens unit, and a positive lens unit, still offers a zoom ratio of about 7xc3x97 to 10xc3x97 and an f-number of about 2.5 to 4. The present invention further offers such high performance that it can be used as an optical system for use with a leading-edge image sensor with a very small pixel pitch.
To achieve the above object, according to one aspect of the present invention, an optical or taking lens device is provided with: a zoom lens system which comprises a plurality of lens units and which achieves zooming by varying the unit-to-unit distances; and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system comprises, at least from the object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a positive optical power. During zooming from the wide-angle end to the telephoto end, the fourth lens unit is moved toward the object side in the zoom range from the wide-angle end to the middle-focal-length position and toward the image-plane side in the zoom range from the middle-focal-length position to the telephoto end. Moreover, the following conditional formula is fulfilled:
9 less than f1/fW less than 30
where
f1 represents the focal length of the first lens unit; and
fW represents the focal length of the entire optical system at the wide-angle end.