pro timecalc

;wht characteristics
;mag=26.	;apparent magnitude of object
;eta=.7		;theory to experimental
;f0=7.17e6	;flux zero point
;texp=3600.	;exposure time
;A=12.47 	;telescope area
;thtel=.78	;telescope throughput
;q=.74		;quantum efficiency
;b=1330.	;bandwidth
;bsky=21.	;sky background mag/arcsec^2
;apix=.237	;arcsec/pixel
;f=.8		;seeing
;r=4.		;readnoise
;      6885.96      38677.8      35.7959      5.83647

;keck characteristics
mag=26.		;apparent magnitude of object
eta=.7		;theory to experimental
f0=7.17e6	;flux zero point
texp=600.	;exposure time
A=76.	 	;telescope area
thtel=.47 ; .78	;telescope throughput calculated from count rates on ESI page
q=.776375	;quantum efficiency
b=1330.		;bandwidth
bsky=20.	;sky background mag/arcsec^2
apix=.15	;arcsec/pixel
f=.85		;seeing
r=2.7		;readnoise
;      7338.38      16511.4      89.3608      6.02508 in .8 seeing
;      7338.38      16511.4      22.3402      11.9617 in .4 seeing

n=10^(-mag/2.5)*f0*eta*texp*a*thtel*q*b		;number of photons from object
s=10^(-bsky/2.5)*f0*eta*texp*a*thtel*q*b*apix^2	;number of photons from sky
p=3.14159265*(f/apix)^2				;area of object

sig=n/sqrt(n+p*(s+r^2))				;signal to noise

print,n,s,p,sig

end