Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-01-29
2003-09-16
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S753000, C359S740000
Reexamination Certificate
active
06621641
ABSTRACT:
BACKGROUND OF THE INVENTION
Generally, a three-color separation optical system is arranged between a lens and the image pick-up planes in a commercial-grade video camera lens that uses three solid-state image pick-up elements. Therefore, a very long back focus has been desired for such a lens in order to accommodate the three-color separation optical system. Recently, solid-state image pick-up elements with a large number of picture elements have been developed in order to obtain a high picture quality. This, in turn, has caused a correspondingly high performance requirement for the camera lens. A so-called retro-focus-type lens has frequently been used to provide a long back focus lens, and such optical systems as disclosed, for example, in Japanese Laid-open Patent Applications H5-134147, and H9-292565 are known.
However, the retro-focus-type lens described in H5-134147 does not form a bright image due to the F
NO
being higher than 1.4. Although a bright image is achieved using the F/1.4 lens described in H9-292565, neither of these lenses is satisfactory in terms of optical performance. Thus, room for lens design improvement exists.
In the case of arranging a three-color separation optical system between a lens and an image pick-up plane, the problem of color shading must be considered. Color shading is a phenomenon that results from the incidence angles of rays onto a dichroic film being different, causing the light path lengths within the thin film to be different. This, in turn, causes the spectral characteristics of a dichroic film to vary, depending on the incidence angle. This, for example, can result in the outgoing rays from a dichroic film which contribute to the upper part versus the lower part of a picture having different colors. Thus, in a wide-angle lens that employs a three-color separation optical system, it is desirable to suppress the occurrence of color shading and to favorable correct various aberrations.
BRIEF SUMMARY OF THE INVENTION
The present invention is a fixed-focus-type camera lens which may be employed in electronic cameras, etc., that use a solid-state image pick-up element. More particularly, the objects of the present invention are to provide a retro-focus-type lens which has a field angle of about 38°, an F
NO
as low as 1.4, so as to provide a high quality image that is especially suitable for HDTV, and which suppresses color shading and has a long back focus.
REFERENCES:
patent: 4431273 (1984-02-01), Nakamura
patent: 5742439 (1998-04-01), Schuster
patent: 5-134174 (1993-05-01), None
patent: 07270680 (1995-10-01), None
patent: 09043511 (1997-02-01), None
patent: 9-292565 (1997-11-01), None
Arnold Bruce Y.
Arnold International
Choi William
Epps Georgia
Fuji Photo Optical Co., Ltd.
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