The spectrograph and the detector
Laboratoire d'Astrophysique de Toulouse - Tarbes (LATT)
et
Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique (LESIA)
The dome and Mehltretter's ring
The dome from outside and Mehltretter's ring in front of the 50 cm two lenses refractor. The metallic ring protects the objective holder against heating and therefore prevents thermal variations in order to preserve image quality and limit instrumental depolarization. (click to enlarge)
The spectrograph
The interior of the dome (click to enlarge)
The spectrograph is a 8 m focal length Littrow type spectrograph, with an Echelle grating (316 lines/mm, blaze angle 63°26'). A MSDP device (Multichannel Subtractive Double Pass) is incorporated for spectro imagery. The spectrograph is usually used at f/120 or at f/180 corresponding to equivalent focal lengths of the telescope of 60 m or 90 m. There is no predisperser, so that we use interference filters (10 nm bandwidth typical) to isolate orders (click to enlarge)
The CCD camera
1997-2005
The camera comes from LaVision (Germany). The CDD is a SVGA 1280 x 1024 pixels detector, manufactured by Sony. It is an interline progressive scan CDD with electronic shutter. The full well capacity is 25000 e, readout noise 8 e and gain 5 e (one ADU = 5 e). The quantum efficiency is 50 % in the blue part of the spectrum. The theoretical throughput is 12 MHz (12 mega pixels/s) but in reality we have only 5.7 MHz (5.7 mega pixels/s). The effective maximum rate is 4.3 frames/s (one frame = 1280 x 1024 pixels x 12 bits), as it requires 230 ms to digitize an image and transfer it to the computer memory (click to enlarge)
2006 and later
The camera comes from LaVision (Germany). The CDD is a 1370 x 1040 pixels detector, manufactured by Sony. It is an interline progressive scan CDD with electronic shutter. The full well capacity is 18000 e, readout noise 5 e and gain 4 e (one ADU = 4 e). The quantum efficiency is 60 % in the blue part of the spectrum. The theoretical throughput is 16 MHz (16 mega pixels/s).
Specifications of the two cameras