If we consider for example a point source with a uniform emission of magnitude 20 in the band B, at 0 days from new moon, being the sky airmass 1.2, and a seeing of 0.5, using a slit width of 2 arcsec, in standard resolution, slow read out mode, grism GRIS-600B inserted, no polarimetry for an integration time of 60 seconds, we get:
where we have used data in Tab. 2.3 and eq. (2.5), (2.6) and expressed the result in Joule units.
Using eq. (2.7):
With the previously specified parameter we can get from formulae in Tab. 2.1:
The ETC for FORS1 with the input parameter as specified above predicts NETC=63 cntsbin.