The invention relates to a projection objective having a variable focal length, preferably serving to image tilting mirror matrices or reflecting and/or transmitting LCDs, more specifically the invention relates to a projection objective comprising three groups of lenses arranged on a common optical axis, wherein, starting from the side facing the projection screen, the first lens group, serving the purpose of focussing, and the second lens group, serving the purpose of varying the focal length, are arranged on the optical axis in a movable manner, and the third lens group is stationary.
Generally known projection objectives having variable focal lengths and used especially for images of the aforementioned type, as described, for example, in EP 058 651 B1 and U.S. Pat. No. 5,644,435, differ from each other essentially in the number of lenses, their arrangement and the technical construction data in connection with the conditions applicable to the optical system.
Since it is desirable for applications, in most cases, to vary the size and location of the image, thus adjusting the projection to the most diverse spatial dimensions, use is made mainly of zoom projection systems.
Therefore, projection objectives consist mainly of a zoom device, a compensating device and a focusing device of the type known from photographic lenses.
As a result in order to achieve a high image quality, such systems comprise many lens elements, are structurally very complex and, thus, very expensive. There is a need in the art for a simple, inexpensive projection objective including relatively few lens elements.
Therefore, it is an object of the present invention, to provide a projection objective of the above-mentioned type, which reduces the technical complexity of its production due to a small number of optical elements having minimized dimensions, while simultaneously ensuring a good imaging performance.
According to the invention, this object is achieved in that the following conditions are met:
1.0 h max<dG2-G3<1.5 h max
and
s≦10 mm,
wherein h max is the maximum object height, dG2-G3 is the distance between lens group G2 and lens group G3 in a first position, and s is the object-side intercept distance. That is, s is the distance from the object side vertex of lens group G3 to the object along the optical axis.
The projection objective according to the invention comprises relatively few optical elements and is, thus, very inexpensive to manufacture.
In order to improve its imaging performance, the projection objective is conveniently designed such that the following conditions are met:
1.2 fl<fG1<1.7 fl,
0.7 fl<fG2<1.1 fl,
1.5 fl<fG3<2.0 fl,
wherein
For example, one embodiment of the invention consists in that, starting from the side facing the projection screen,
Advantageous further embodiments of the projection objective according to the invention consist in that the following conditions are met:
2.0<L/fl<30
1.68<navg<1.74
40.0<vavg<44.0,
wherein
The projection objective according to the invention will be explained in more detail with reference to embodiment examples. In doing so, identical reference numerals designate identical elements in the individual Figures.
In this example, the lens group G2 consists of a positive meniscus lens 6 and a negative meniscus lens 7 (assembly), of a positive lens 8 and of a positive assembly consisting of a positive lens 9 and of a negative lens 10.
The lens group G3 is characterized by a positive lens 11.
In variation of the example according to
Analogous to this type of representation,
The present invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.
Number | Date | Country | Kind |
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102 44 586 | Sep 2002 | DE | national |
Number | Name | Date | Kind |
---|---|---|---|
5644435 | Shikama | Jul 1997 | A |
6137638 | Yamagishi et al. | Oct 2000 | A |
6301058 | Nagahara | Oct 2001 | B2 |
6317269 | Yamamoto | Nov 2001 | B1 |
6515803 | Hirose | Feb 2003 | B2 |
6542311 | Nagahara | Apr 2003 | B2 |
6545817 | Hirose | Apr 2003 | B2 |
6563650 | Moskovich | May 2003 | B2 |
6590716 | Narimatsu | Jul 2003 | B2 |
6636361 | Wada | Oct 2003 | B2 |
20020145809 | Okuyama | Oct 2002 | A1 |
Number | Date | Country |
---|---|---|
0 058 651 | Aug 1982 | EP |
0 585 651 | Jun 2000 | EP |
Number | Date | Country | |
---|---|---|---|
20040125464 A1 | Jul 2004 | US |