[ ESO ] La Silla


Instrumental Overview

Since 1998, the Nasmyth focus A at the NTT telescope has hosted two instruments: the IR imager-spectrometer SOFI, and the direct imaging CCD camera SUSI2. The latter is an upgraded version of the SUperb Seeing Imager, identical in concept (imaging at the f/11 focus of the telescope with one additional reflection), but with 4 times the field of view (5.5 x 5.5 arcmin). SUSI2 uses a FIERA controller to drive a mosaic of two 2k x 4k, 15 µm pixel, thinned, anti-reflection coated EEV CCDs. Other novel features of the instrument are an 8cm x 8cm sliding curtain shutter which permits uniform exposures down to 0.3 seconds, and a special cryostat designed to operate on a rotating Nasmyth adaptor. SUSI2 and SOFI share the same mechanical structure attached to the Nasmyth adaptor flange and the same cable derotator. The direct beam from the telescope feeds SOFI. A 45° mirror is inserted in the light path when SUSI2 is in operation.

Optical Components

The optical path of SUSI2 includes the three mirrors of the telescope, the 45° reflection prism with a multi-layer coating (reflection efficiency > 90% in the range 340-500 nm; > 95% in the range 500-1100nm; known as "Mirror 4" in the NTT jargon), and the coated quartz window of the cryostat (transmission > 97% over the range 340-1100 nm).

The filter wheel and the shutter are located at f/11 between the prism and the cryostat.  Before Nov.1999, there was a small vignetted region at the bottom the the CCDs (~500pix). While the vignetting could be flat-fielded out, this region should not be used for accurate photometry. The vignetting was caused by mirror 4, whose position has subsequently been adjusted.

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Last modified: Tue Nov 4 2003 
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