System Throughput and SNR / Exposure Time Estimation
The presence of significant red leaks in the UV filters, together with the much greater sensitivity and wavelength coverage in the red part of the spectrum, can make UV observation and calibration difficult. Observers must sometimes be prepared to take additional frames at red wavelengths, in order to estimate the contribution of red leak to the UV counts. The counts contributed by red leak can be a significant noise source, and must also be taken into account during SNR and exposure time estimation. See section 3.8 on page 57 for detailed information. Note that the SYNPHOT synthetic photometry package can be used to estimate counts due to red leak for particular filter / target combinations.