Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
1999-09-28
2001-09-04
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S683000
Reexamination Certificate
active
06285509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to zoom lenses suited to be used in display apparatuses, for example, projection apparatuses for displaying an original image onto a screen in an enlarged scale and, more particularly, to a zoom lens of simple design in a compact form suited to be used in a projection apparatus of the type in which three images of original colors on individual liquid crystal display panels or like displays are combined to form the original image in high definition and are then projected by only one projection lens.
2. Description of Related Art
The zoom lens whose front lens unit is negative in refractive power, that is, of the negative-lead type, has the advantages that the maximum field angle is relatively easy to increase and the image quality is kept stable in close-up photography. On the other hand, the zoom lens of the negative-lead type the such disadvantages that the zooming movement becomes longer and the zooming range is difficult to increase.
With these disadvantages in mind, zoom lenses of an increased range, while still permitting the bulk and size of the entire system to be reduced to a compact form, are disclosed in, for example, Japanese Patent Publication No. Sho 49-23912 and Japanese Laid-Open Patent Applications No. Sho 53-34539, No. Sho 57-163213, No. Sho 58-4113, No. Sho 63-241511 and No. Hei 2-201310.
In these publications, the zoom lens comprises four lens units of minus-plus-minus-plus refractive power arrangement in this order from the object side. Of the four lens units, predetermined ones are made to axially move in proper relation to effect zooming.
It is known to provide an apparatus for displaying an image on a screen in an enlarged scale by projection, in particular, an apparatus of a type in which a plurality of images of original colors on the respective individual liquid crystal display panels are combined to form an image in the gamut of colors, which is then projected by the projection lens. To adapt the negative-lead type zoom lenses mentioned above for application to such a projection lens, it becomes necessary to satisfy the following various conditions.
(i) The liquid crystal display panel has radiation characteristics and the assembly of dichroic mirrors suffers angle dependence in combining the plurality of images of original colors. In order to remove the influence of either of these factors, the optical system to be used should have the pupil as viewed from the display panel (the pupil as viewed from a shorter conjugate point side) put at a remote distance, or should be a so-called telecentric one.
(ii) The back focal distance should be long enough to secure the space the color combining elements occupy between the display panel assembly and the projection lens.
(iii) The image-bearing light beam is usually skewed upward as is projected onto the screen. So, the display panel assembly is arranged with its center shifted out of the optical axis. As a result, in a region near the front lens members, the effective area to use is not symmetrical with respect to the optical axis, but deviates upward. To allow this, the diameter of the front lens members necessarily becomes large. This must be obviated to reduce the bulk and size of the front lens members as far as possible.
Regardless of such requirements, in the prior art as previously mentioned, the pupil as viewed from a shorter conjugate point side lies at a finite distance and the back focal distance, too, cannot be said to be long enough.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to eliminate the above-described problems and to provide a zoom lens suited to the projection lens in the display apparatus.
To attain the above object, in accordance with an aspect of the invention, there is provided a zoom lens for projecting an original image onto screen in an enlarged scale, which comprises, in order from the screen side, a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of negative refractive power, a fourth lens unit of positive refractive power and a fifth lens unit of positive refractive power, wherein, during zooming from a wide-angle end to a telephoto end, the second lens unit and the fourth lens unit move toward the screen side.
The above and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.
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Nakayama Hiroki
Nishio Akihiro
Sugawara Saburo
Canon Kabushiki Kaisha
Epps Georgia
Fitzpatrick ,Cella, Harper & Scinto
Thompson Tim
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