[Rainbowline]

Overall Efficiency

The efficiencies of the subcomponents of the instrument as well as the overall efficiency including the fibers and the CCD are given in the following table. The column ``Pre Slit'' includes the micro lens, the fiber, the F/N lens and the image slicer. The efficiency of the first three components is taken from the glas and coating data sheets multiplied by the coupling efficiency of the fiber of 75% and the assumed lower limit of 90% efficiency for the image slicer. The values in the column ``Echelle'' were measured by ESO in 1996. The efficiencies given for the CCD are the design goals for the thinned and back-illuminated 2kx4k EEV chip.

Wavelength [Å] Pre Slit Mirrors Echelle Crossd. Camera CCD Total
3500 0.50 0.24 0.73 0.55 0.70 0.50 0.017
3700 0.52 0.52 0.73 0.79 0.80 0.58 0.07
4000 0.56 0.92 0.73 0.90 0.85 0.72 0.21
4500 0.57 0.94 0.73 0.91 0.85 0.85 0.26
5000 0.58 0.96 0.73 0.91 0.85 0.85 0.27
6000 0.59 0.94 0.73 0.89 0.85 0.85 0.26
7000 0.60 0.94 0.73 0.88 0.85 0.78 0.24
8000 0.60 0.92 0.73 0.87 0.85 0.55 0.16
9000 0.60 0.92 0.73 0.86 0.85 0.28 0.08

Assuming these efficiencies and an efficiency of 60% for the 1.52-m telescope, a spectrum of a 10th magnitude star can be taken in 15 min with a S/N=100 per pixel in V (cf. figure below). Within one hour for a star of 16th magnitude star still a S/N of 10 is reached.

These numbers were derived assuming a slit length of 10 pixels, each pixel contributing with a read-out noise of 3 electrons and a dark current of 4 electrons/hour as given by the CCD characteristics.

[Signal-to-Noise-Ratio]

Recently updated total efficiencies

The following plot is regularly updated with measured efficiencies of the individual components. Finally, we will have here the system efficiency measured from sky to detector as function of wavelength.

[System Efficiency]

Updated on August 18, 1998 (includes now measured efficiencies of microlens, fiber, F/N system, image slicer, echelle, collimators, crossdisperser prims, camera, field lens, and science grade detector (measured by EEV). [Rainbowline]

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FEROS homepage / A.Kaufer@lsw.uni-heidelberg.de
Last modified: Fri Jan 26 10:45:00 MET 2001