Design method for zoom systems based on tunable lenses

It is well known that tunable lenses, with refractive power that can be varied, e.g., by changing the curvature of a membrane, can replace the motion of lens groups in zoom systems. Similar to classical zoom systems, the performance of these systems is heavily influenced by the fundamental first-order layout. Moreover, the first-order layout sets the most important requirements for the employed tunable lenses. In this contribution, we present a method for the analysis of a large number of possible first-order solutions for typical requirements and for the selection of the most promising layouts. The first-order solution space is mapped, allowing the layouts to be automatically filtered and plotted depending on pre-defined characteristics. Ray tracing of the marginal and chief rays combined with the traditional thin lens aberration theory provide efficient estimations of the expected installation space requirements and performance for each first-order layout. Using an example, we demonstrate good agreement between these estimations and the corresponding real lens layout, optimized by commercial raytracing software. The presented design method for zoom systems based on tunable lenses is compared with similar approaches for classical zoom lenses

Chromatic aberration theory in modern metrology

Hyperchromatic systems are especially used in chromatic confocal metrology to measure distances, layer thicknesses, and object surfaces. The correction of the spherical aberration for all wavelengths is an essential requirement for the design of such systems. We present general techniques for the methodical design of hyperchromatic systems with large longitudinal chromatic aberration. The proposed techniques are applied to design a contact-free wall thickness measuring device. Large tilting angles of up to 20° in combination with an extra long measuring range of 18mm and a minimum working distance of 35mm require a high speed optical system. We discuss the problems arising during the design of a system that realizes high lateral resolution within the whole measuring range. Furthermore we demonstrate the optimization of optical systems which image different wavelengths onto different image planes

Zoom systems with tunable lenses and linear lens movements

Background: Classical zoom lenses are based on movements of sub-modules along the optical axis. Generally, a constant image plane position requires at least one nonlinear sub-module movement. This nonlinearity poses a challenge for the mechanical implementation. Tuneable lenses can change their focal length without moving along the optical axis. This offers the possibility of small system lengths. Since the focal range of tuneable lenses with significant aperture diameters is still limited, the use of tuneable optics in zoom lenses is usually restricted to miniaturized applications. Methods: To solve the challenge of the nonlinear movement in classical zoom lenses and the limitations of tuneable lenses for macroscopic applications we propose a combination of both concepts. The resulting ‘Hybrid Zoom Lens’ involves linear movements of sub modules as well as changing the focal length of a tuneable lens. The movements of the sub-modules and the focal length tuning of the lens are already determined by the collinear layout of the zoom lens. Therefore, we focus on collinear considerations and develop a method that allows a targeted choice of specific collinear layouts for our ‘Hybrid zoom lenses’. Results: Based on examples and an experimental setup we demonstrate the feasibility of our approach. We apply the proposed method to examples of classical zoom lenses and zoom lenses based exclusively on tuneable lenses. Thereby we are able to show possible advantages of our ‘Hybrid zoom lenses’ over these widespread system types. Conclusions: We demonstrate important collinear considerations for the integration of tuneable lenses into a zoom lens. We show that the combination of classical zoom lens concepts with tuneable lenses offers the possibility to reach smaller system lengths for macroscopic zoom lenses while requiring only a small focal tuning range of the tuneable lens

Untersuchungen zur Genauigkeit NURBS-basierter optischer Freiformflächen

Freiformflächen bieten als symmetriefreie Flächen eine Vielzahl von Freiheitsgraden bei der Lösung nicht rotationssymmetrischer Abbildungsaufgaben. Dies erlaubt es einerseits, die Zahl der optischen Elemente zu reduzieren, wodurch Material-, Gewichts- und bei entsprechenden Replikationsverfahren auch Kosteneinsparungen möglich sind. Andererseits werden neue Anwendungsbereiche erschlossen, die mit sphärischen und asphärischen Flächenformen nicht realisierbar waren. Seit geraumer Zeit haben sich Non-Uniform Rational B-Splines (NURBS) als Standard im Computergrafik- und CAD-Bereich etabliert. Im Gegensatz zur im Optikdesign weit verbreiteten Polynomdarstellung bieten sie eine wesentlich höhere Flexibilität und sind gleichzeitig in verschiedenen Datenaustauschformaten implementiert, sodass eine direkte und verlustfreie Anbindung an die Fertigung möglich ist. In diesem Beitrag wird untersucht, inwiefern NURBS – Flächen eine ausreichende Genauigkeit für die Beschreibung von komplexen, abbildenden optischen Komponenten bieten. Gleichzeitig wird analysiert, mit welchem Aufwand eine beugungsbegrenzte Abbildung realisiert werden kann