An active optics concept for the multi-object spectrograph EAGLE

The reliability of active optic for telescopes and instrumentation is now good enough to make them available for day to day use in working observatories. Future telescopes and their associated instruments will benefit from this technology to offer innovative concepts, optimal performance and improved reliability. An optical design of the multi-objects spectrograph EAGLE using, active surfaces, is detailed in this article. The first active component is a steering mirror, included in the target acquisition system, able to compensate for large astigmatism variations due to the variable off-axis design. This innovative design also includes two variable curvature mirrors authorising focus compensation and adding a zoom facility. A complete description of these active mirrors mechanical principle is presented, from elasticity theory to opto-mechanical design. The prototypes of these active mirrors with their complete test bench are detailed.