expose.param:

	15.0            ! magnitude limit
	100.0           ! S/N
	5.0             ! Photometry aperture (radius in arcsec)
	0.61            ! Effective Telescope Diameter (meters)
	15              ! Readnoise (e- rms)
	0.57            ! plate scale (arcsec/pix)
	0.7             ! Wavelength independent throughput
	qe.TEK24        ! CCD quantum efficiency file (list: UBVRI JHK griz)
	sky.SC          ! Sky brightness file (list: UBVRI JHK griz)

   expose output:

	#                 S/N =  100.00
	# photometry aperture =   78.54    (arcsec^2)
	#      telescope area =    0.29         (m^2)
	#          read noise =   15.00      (e-/pix)
	#         plate scale =    0.57  (acrsec/pix)
	#        photons/  
	# Band   m^2-sec    sky      e    m(lim)  t(rn)[sec] t(snr)[sec]
	#         (m=0)    
	    U   0.410E+10  20.80   0.070  15.00   0.471E+03   0.372E+03
	    B   0.142E+11  21.50   0.140  15.00   0.785E+02   0.519E+02
	    V   0.879E+10  20.30   0.280  15.00   0.474E+02   0.453E+02
	    R   0.107E+11  19.50   0.350  15.00   0.221E+02   0.339E+02
	    I   0.732E+10  18.40   0.175  15.00   0.328E+02   0.145E+03

NOTE that expose.f uses two input lists: qe.TEK24 and sky.SC. These
currently contain VERY rough guesses for the detector QE and sky
brightness. The column headed 't(rn)[sec]' gives the time to reach
background or source limit on a given exposure. In general, your
exposures should be several times this value, all else being equal
(e.g. if guiding/tracking is not an issue). The column headed
't(snr)[sec]' gives the total time to reach the specified S/N.