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General information
on the SOFIA telescope
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SOFIA Telescope



Under an agreement with NASA, DLR (the German Aerospace Center) will supply the telescope for the SOFIA observatory as well as operation support in exchange for observation time aboard the SOFIA.

The SOFIA telescope is designed as a Cassegrain system with two Nasmyth foci, the nominal IR focus and an additional visible light focus for guiding. IR light is reflected off the upper tertiary mirror, which has a dichroic coating. The dichroic can be replaced with a fully reflective mirror if guiding with the focal plane guider is not required.

It has a parabolic 2.7m primary mirror and a hyperbolic secondary mirror. The secondary mirror is attached to a chopping mechanism providing chop amplitudes of up to ± 5 arcmin at chop frequencies between 0 and 20 Hz, programmable by either a user supplied analogue or TTL curve or by the telescope control electronics. A flat tertiary mirror reflects the beam into the infrared Nasmyth focus, 300mm behind the instrument flange. If the tertiary is replaced by a dichroic mirror, the transmitted optical light is reflected by a second tertiary 289.2mm behind the dichroic and sent to the visible Nasmyth focus. There it is fed into a focal plane guiding camera system (FPI). Independent of the FPI there are two other imaging and guiding cameras available: the wide field imager (WFI) and the fine field imager (FFI). Both of these cameras are attached to the front ring of the telescope.

image showing the optical system of the telescope


Page Last Updated: March 10, 2004

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