The following sources provide data on stars suitable for photometric calibrations. Remember that for short exposures the variation in the shutter "fly time" may dominate the photometric accuracy of your result. One way around this is to define a set of "secondary" standards in the field which are relatively fainter than the standards given below. A short (say, 1 second) exposure may give a good exposure on the primary standards, and sufficient exposure in a number of fainter field stars. Then a longer (say, 10 second) expsoure will still leave the fainter stars unsaturated, but will have only a fraction (1/10 in the example given) of the uncertainty due to variation in the time it takes to open and close the shutter. The ratio of fluxes of the faint stars in the short and long exposures is also the ratio of the effective exposure times of the two exposures, allowing you to infer a more accurate exposure for the first, short exposure. This then allows a more accurate calibration of the primary standards. Note that as long as the exposures are taken with the same filter there is no need to know the colors of the fainter field stars (the "secondary" standards).
UBVRI photometric standard stars in the magnitude range 11.5-16.0 around the celestial equator
Landolt, A. 1992, AJ, 104, 340 [ table | paper ]

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