This form allows you to calculate ULTRACAM count rates and
signal-to-noise ratios for the WHT, VLT and NTT. The WHT calculation is
based on measured zero points for the u', g', r', i' and z' filters
and should therefore be accurate to approximately 5% in object counts.
The VLT and NTT calculations are based on the WHT values, but scaled to take
into account the different telescope apertures, the extra reflection at
Nasmyth and the different pixel scales. The VLT and NTT sky brightness,
extinction and telescope throughput are therefore assumed to be
identical to the WHT, reducing the accuracy of the results.
If you don't know the SDSS magnitude of your target, you can use the formulae in Table 7 of Smith et al. (2002, AJ, 123, 2121; astro-ph/0201143) or this little f77 program to convert from UBVRI to u'g'r'i'z' magnitudes.