A set of default rules is provided for classifying the EMMI/SUSI frames 
according to their exposure types and optical paths.
By default frames are classified according to the following scheme:

BIAS:   exposure time .EQ. 0 
DARK:   exposure time .GT. 0  .AND.  shutter closed
FFLAMP: lamp .EQ. "FF-BLUE" .OR. lamp .EQ."FF-RED".OR.
	lamp .EQ. "LAMBDA-R" .OR. lamp .EQ. "LAMBDA-B"
FFDOME: ident .EQ. "~*FF*" .AND. telescope in dome ff position
FFSKY:  ident .EQ. "~*SKY*" .AND. altitude .GT. 32 degrees
FFSKY?: ident .EQ. "~*FF*" .AND. altitude .GT. 32 degrees
WCAL:   acquisition system supplied exposure type .EQ. "CAL" .AND. 
	lamp present
FOCUS:  grism .EQ. "FOCW" .OR. 
        acquisition system supplied exposure type .EQ. "FOI" .OR.
        acquisition system supplied exposure type .EQ. "FOC" .OR.
SCI;    none of the above 

By default the optical path is categorized by a character string which is built
from the optical elements used:
Red Imaging:                RFILT_filter#(filtername)
Blue Imaging:               BFILT_filter#(filtername)
Susi Imaging:               SFILT_filter#(filtername) 

Grism  Spectroscopy:        RFILT_filter#(filtername)+GRISM_grism#
Red Grating Spectroscopy:   RGRAT_grating#(central wavelength)
Blue Grating Spectroscopy:  BGRAT_grating#(central wavelength)
Echelle Spectroscopy:       GRISM_grism#+GRAT_grating#
Dichroid Mode Spectroscopy: RGRAT_grating#(central wavelength)+
                                              BGRAT_grating#(central wavelength)