Photocopying – Projection printing and copying cameras – Focus or magnification control
Patent
1990-09-27
1991-10-01
Wintercorn, Richard A.
Photocopying
Projection printing and copying cameras
Focus or magnification control
355 60, G03B 2734, G03B 2740, G03B 2770
Patent
active
050538101
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a reprographic lens system consisting of first, second and third subsystems aligned about the optical centre of the system. The first subsystem comprises a first zoom lens, the second subsystem a field lens and the third subsystem comprises a second zoom lens.
In known reprographic cameras it is necessary to use vertically movable mechanical adjustments. This is due to the fact that with objectives with fixed focal lengths it is necessary to adjust the distance between object and image to achieve the desired reproduction ratio. This implies that it is often the guiding mechanism of the camera setting in practice the limits to the reproduction ratio and thus to the usable range. Accordingly, it has so far been necessary to use lens systems with exchangeable/readjustable optics.
The object of the present invention is to provide a lens system which can be constructed from components known per se and in which the lens system has variable focal length for providing reproduction ratios within a large reproduction interval. Furthermore, the object is to provide a reproduction apparatus for carrying out the invention in such a way that the reprographic camera includes as few movable components as possible.
This is obtained according to the invention in that the field lens is arranged to reproduce the outlet aperture of the first zoom lens in the inlet aperture of the second zoom lens. In such a construction of the lens system a far higher flexibility is achieved than obtained until now as it is hereby possible to reproduce within a large magnification interval with the same optics and without the need for translatory movement of guiding elments for changing the distance between the object plane and the image plane.
In practice, the fewer movable parts mean that a generally simplified constrcution and control of the camera is achieved and, moreover, a greater accuracy in eliminating the error possibilities from the curvilinearity and linearity irregularities from the guiding elements of the conventional reprographic camera.
The lens system is likewise advantageous for application in connection with the types of reprographic cameras in which the object plane and the image plane are in the same plane. Such an apparatus is typically provided with reflective means, like mirrors or prisme bending the path of beams and which are, moreover, translatorily movable for variation of the magnification. It is evident that the application of the lens system according to the invention in this type of apparatus makes the use of horizontally movable mirrors obsolete as the lens system performs the changes in focal lengths.
The invention will now be explained in more detail with reference to the drawings, in which
FIG. 1 schematically illustrates an embodiment of a lens system according to the invention,
FIG. 2a and 2b illustrate the lens system provided with further elements, and
FIG. 3 illustrates an embodiment of a reprographic camera according to the invention.
FIG. 1 is a schematical view of a lens system according to the invention. The lens system consists of three main elements 1, 2 and 3. The elements may consist of a number of sections which for the sake of clearness are not shown.
Element 1 produces a real image of the object 4 in a plane 5 coinciding with the plane of symmetry of lens element 2, and element 3 produces a real image 6 of the object 4 in a plane 7.
Lens element 2, the field lens, is formed so that it reproduces the outlet aperture of lens element 1 in the inlet aperture of lens element 3. This provides for obtaining a maximum transfer of light energy from lens element 1 to lens element 3.
According to the present invention lens elements 1 and 3 are formed as elements with variable focal lenth, so-called zoom lenses. In a preferred embodiment these are desgined so that their outlet apertures are in a fixed plane, irrespective of the instantaneous adjustment of the focal length. However, this is no limitation in practice.
In the practical structure of the lens system according to the i
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Helioprint A/S
Wintercorn Richard A.
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