After a brief introduction of the SDSS-V optical instrumentation installed at the Apache Point 2.5m telescope, the presentation will be mainly focused onto the optical production and testing of the 3 large lenses (diameter 700-800mm) constituting the wide field optical corrector (WFC). Special emphasis will be made onto the measurement issues and solutions of the deep aspherical surfaces as well as the review of the specific anti-reflection (AR) coating with development of a dual band anti-reflective coating, carried out by Thales SESO-France. Before concluding, a dedicated paragraph will address on-sky imaging performances results with this new WFC. The presentation will conclude by a brief overview of the corresponding existing “state of the art” at Thales SESO for future manufacturing of similar or large optics for next generation of very wide field corrector.
Regarding the progress of optical design in favor of freeform surfaces, it becomes necessary to scale their feasibility with appropriate criteria in order to get a standard between an optical designer and an optical manufacturer. Two criteria are necessary, one linked to polishing process and one appropriate for measurement limitation. First criterion can be the extension to freeform surfaces (defined here by first Zernike terms) of a previous criterion which was calculated using conical equation. This criterion is representative of surface’s curvatures fluctuations which limit polishing efficiency and can generate high frequency defects. The second criterion should take into account the difficulty to measure the surface as feasibility needs also good knowledge of the correction polishing cycle to be performed. Different solutions exist for an accurate measurement in the range of nm. As demonstrated in the article, slopes versus reference surface is the limiting factor for a majority of measurement solutions. Therefore the criterion will be linked to a slope parameter. The governing principle of these criteria is to remain close to some relevant physical dimensions. In this idea, the polishing feasibility criterion defined in this paper will be comparable to tool diameter of Computer Controlled Polishing which refers to equipment resolution of optical manufacturers. In the same idea, we project to define a dimensioned criterion for measuring feasibility which can be compared to engraving resolution for a given Computer Generated Hologram.
After a brief introduction of what is the Dark Energy Survey (DES) project and which optical instrumentation will be
used, the presentation will be mainly focused onto the optical production of the large lenses (up to 1m diameter)
constituting the DES Camera (DECAM) located at the focal plane of the main observing telescope. Special emphasis
will be made onto the optical manufacturing issues and interferometric testing solutions, including compensation of
index inhomogeneities, which have been carried out by THALES SESO especially for the biggest entrance lens (very
challenging CV/CX meniscus named C1). Through several examples of typical past realizations or future possible
ones for different astronomical projects requiring 1m-class optics, the presentation will conclude by a brief over
review of the corresponding existing "state of the art" at THALES SESO for these technologies.
After a brief introduction of what is the Dark Energy Survey (DES) project and which optical instrumentation will be
used, the presentation will be mainly focused onto the optical production of the large lenses (up to 1m diameter)
constituting the DES Camera (DECAM) located at the focal plane of the main observing telescope. Special emphasis
will be made onto the optical manufacturing issues and interferometric testing solutions, including compensation of
index inhomogeneities, which have been carried out by SESO especially for the biggest entrance lens (very challenging
CV/CX meniscus named C1). Through several examples of typical past realizations or future possible ones for different
astronomical projects requiring 1m-class optics, the presentation will conclude by a brief over review of the
corresponding existing "state of the art" at SESO for these technologies.
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