ESO MULTI-MODE INSTRUMENT: RILD MODE
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  Instrument Overview                                                         
  ===================                                                         
    The ESO Multi-Mode Instrument (EMMI) is a multipurpose instrument allowing
    observations in thevisible wavelengths. EMMI supports wide-field imaging, 
    low-resolution multi-object or long-slit grism spectroscopy,              
    medium-resolution long-slit grating spectroscopy, and echelle             
    spectroscopy, using various detector modes.                               
                                                                              
    The RILD mode, for low-dispersion spectroscopy, is described here.        
    Low-resolution long-slit spectroscopy is done in the RILD mode by         
    combining one of the grisms with one of the fixed slits (starplates) and, 
    if needed, an order-sorting filter. The grisms cannot be rotated: the     
    achievable wavelength range is fixed for each grism.  Many grisms show a  
    second order contamination, hence the use of an order sorting filter is   
    recommended.                                                              
                                                                              
    There are six fixed slits available, with widths of 0.5, 1.0, 1.5, 2, 5   
    and 10 arsec, and each with a length of 8'. The 0.5 arsec slit will cause 
    undersampling of the spectra, except when used in 1 x 1 binning mode,     
    under exceptional seeing conditions.                                      
                                                                              
    The orientation of the slit can be adjusted by applying an offset to the  
    rotation angle of EMMI.                                                   
                                                                              
    Grisms and filters can also be combined to obtain slitless spectra imaged 
    on the CCD. The use of filters in combination with a grism reduces the sky
    background intensity. It also selects the wavelength region of interest   
    and limits the length of the spectrum, thus reducing crowding. The        
    spectral coverage within this wavelength region depends on the position of
    the object in the field.                                                  
                                                                              
    The following table summarizes the Grisms available on EMMI and their     
    characteristics.                                                          
                                                                              
    Grism g/mm Blaze Blaze  Eff.[a]  Dispersion[d]   Rs[b] Wavelength range   
               angle lambda                                                   
               (deg) (nm)     (%)   (nm/mm) (A/pix)            (nm)           
    ------------------------------------------------------------------------  
    1     150   8.6   560     79     24.5    3.68    263      385 - 1000 [c]  
    2     300  14.6   490     78     11.6    1.74    570      380 - 920 [c]   
    3     360  15.0   460     77      9.4    1.43    760      380 - 907 [c]   
    4     300  22.0   650     72     11.6    1.76    613      550 - 1000      
    5     600  34.0   530     66      5.5    0.83   1100      380 - 702       
    6     600  54.0   650     55      5.0    0.73   1490      575 - 867       
    7     150  10.8   720     80     24.0    3.62    280      490 - 1000 [c]  
                                                                              
    [a] Efficiency at blaze.                                                  
    [b] Resolution with 1' slit at 600 nm (at central lambda for grisms 4,5   
    and 6) and for binning 2                                                  
    [c] Second overlap occurs beyond 800 nm if not using an order-sorting     
    filter.                                                                   
    [d] Dispersion with 1 x 1 binning