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All-reflective optical power zoom objectives

: Grüger, Heinrich


Betensky, Ellis (Ed.) ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Zoom lenses V : 10 - 13 August 2015, San Diego, California, United States; Fifth SPIE Conference on Zoom Lenses
Bellingham, WA: SPIE, 2015 (Proceedings of SPIE 9580)
ISBN: 978-1-62841-746-3
Paper 95800H, 13 S.
Conference on Zoom Lenses <5, 2015, San Diego/Calif.>
Fraunhofer IPMS ()

Over the past decades zoom lenses have become an important type of objective. Due to their ability to dynamically change magnification or field angle they are being used in many fields of application. Most zoom lenses consist of a number of lenses or lens groups. The magnification can be changed by axial shifting some of these lens groups with a more or less complicated moving function.
However, in principle it should be possible to construct zoom lenses that do not rely on the movement of some of its components. Instead, the change in magnification is achieved by changing the optical power of at least two lenses within the system (optical power zoom - OPZ). Moreover, for broadband applications it is highly favorable to use mirrors instead of lenses due to the absence of chromatic aberrations.
Based on a "Schiefspiegler" approach an all-reflective OPZ objective with a zoom power of three consisting of four mirrors has been designed. Two mirrors are assumed to have a variable radius of curvature for changing optical power. During aberration correction special consideration has been given to the reduction of field curvature, since the optical power change strongly influences field curvature for different zoom positions. The simulation shows adequate image quality for photographic applications over the whole zooming range.
For the realization of such an OPZ objective deformable mirrors with a comparatively large stroke are needed. Before starting a complex development of such devices three setups with different fixed focal lengths were built to prove and evaluate the concept for digital imaging.