Thats a useful looking book. Will grab a copy off ebay.
The calcs I am doing are based around the standard CCD S/N calculation mentioned by Steve Howell in his “Handbook of CCD Astronomy” – derived from Mortara&Fowler plus Newberry and others
Something like…
SNR=Nstar*t/sqrt(Nstar*t+npix(Nsky*t+Ndark*t+Nread*Nread))
where:
t – exposure length
Nstar – electrons from the star
npix – number of pixels covered by star
Nsky – electrons from sky in each pixel
Ndark – dark current electrons
Nread – read noise