For a given optical configuration (channel, PFOV and Filter or CVF ), using figures to , find :
= ordinate of the solid line for the filter or CVF at
In a first approximation, the dark noise, the flat-field noise and the low frequency noise can be neglected.
Taking and S/N the expected flux of the source and the needed S/N ratio of the observation, compute:
If this observation should be easy to do, you can choose the parameter of the figure, or even try to scale down , but not much since the minimum number of exposures is 4. You could possibly shorten the observation time by taking a shorter integration time, then increases roughly like .
If , increasing improves S/N like as long as long as the low frequency noise does not get predominant. Checking with the following detailed calculation is recommended.