Optical: systems and elements – Lens – With variable magnification
Patent
1998-02-12
1999-11-02
Epps, Georgia
Optical: systems and elements
Lens
With variable magnification
359683, G02B 1514
Patent
active
059781521
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a zoom lens system for use in a single-plate video camera, etc., having a wide angle of view (59 degree or greater) and a high zoom ratio (approximately 10.times.).
BACKGROUND ART
Size reduction of image pickup devices and size reduction of lens systems is greatly demanded in today's video camera market. Moreover, it is an important factor that electronic still-video cameras which have appeared in recent years with the spread of multimedia personal computers are inexpensive and small in size. On the contrary, for the manufacturers, it is necessary to reduce the cost in order to have competitive power in the market. In order to reduce lens systems in cost, it is necessary to provide a construction of lens system which has a minimum number of lens elements and is capable of maintaining performance the same as or higher than that of conventional lens systems while having a minimum number of lens elements.
For these reasons, it has conventionally been a problem how a zoom lens system is provided to be is small in size and high in resolution but has a fewer number of lens elements.
A conventional zoom lens system will be described.
FIG. 32 is a view showing the structure of a conventional zoom lens system for use in a video camera described, for example, in Japanese Laid-open Patent Publication Number Hei 6-109975. The zoom lens system shown in the figure comprises a first lens unit 321 serving as a condenser unit, a second lens unit 322 serving as a zooming unit, a third lens unit 323 serving as a condenser unit, a fourth lens unit 324 serving as a focusing unit, an equivalent glass plate 325 corresponding to a crystal filter or a faceplate of an image pickup element, etc., and an image forming plane 326.
The first lens unit 321 fixed in relation to the image forming plane 326 has imaging function, and the second lens unit 322 moved back and forth along the optical axis varies the magnification thereby to vary the focal length of the overall lens system. The third lens unit 323 which is a stationary unit condenses light diverged by the second lens unit 322, and the fourth lens unit 324 moved back and forth along the optical axis has focusing function. Moreover, the variation in position of the image plane caused by the movement of the second lens unit 322 during zooming is corrected by the movement of the fourth lens unit 324 so as to image in a fixed position, whereby the image plane is always maintained in a fixed position.
However, in the conventional zoom lens system as described above, what is called f-number is 1.6 or higher although the number of lens elements is ten and the zoom ratio is approximately 10.times.. Therefore, it cannot cope with the insufficient sensitivity which is a problem in reducing of image size. Moreover, although having a small number of lens elements, its overall length is comparatively large and it lacks compactness. For this reason, it is a problem that the conventional zoom lens system cannot fulfill the harsh demand for zoom lens systems for video cameras which is to be smaller in size and has higher performance. Moreover, it is difficult for the conventional zoom lens design technique to produce a zoom lens system which fulfills all of a large aperture, a high magnification, a smaller size and a higher resolution.
DISCLOSURE OF INVENTION
The present invention is intended for solving the above-mentioned problems and an object of the present invention is to provide a very compact zoom lens system with an f-number of approximately 1.4 and a zoom ratio of approximately 10.times. although having a simple lens arrangement including ten lens elements, by employing an optimum lens arrangement and an optimum aspherical configuration. Another object is to provide a small-size video camera and a small-size electronic still camera, etc. using the zoom lens system.
A zoom lens system of the present invention is that, in a certain structure having a first lens unit to a fourth lens unit, the respective lens units are structured as fo
REFERENCES:
patent: 5313331 (1994-05-01), Mihara
II Hisayuki
Kakimoto Tsuyoshi
Okayama Hiroaki
Ono Shusuke
Epps Georgia
Matsushita Electric - Industrial Co., Ltd.
Schwartz Jordan M.
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