CDROM/AJ/V105/P1206 Twilight Flats (Tyson & Gal 1993) ================================================================================ An Exposure Guide for Taking Twilight Flatfields with Large Format CCDs Neil D. Tyson & Roy R. Gal <1993, AJ, 105, 1206> =1993AJ....105.1206T ================================================================================ Abstract: Driven by the long readout times of today's large format CCDs, we present an efficient method to compute an ideal sequence of exposure times for twilight skyflats. The procedure will allow the observer to maximize the number of flats that can be obtained in the rapidly changing surface brightness of the dusk or dawn sky. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- table3.dat 132 209 Exposure sequences twilight.f 71 198 FORTRAN 77 program that generated table3.dat -------------------------------------------------------------------------------- Comments for file: table3.dat -------------------------------------------------------------------------------- Rows of exposure sequences are provided (in seconds) for CCD readout times that range from 15 seconds to 6 minutes. The wide table assumes a twilight coefficient: tau = 1 (spring/autumn at 30 degrees latitude). -------------------------------------------------------------------------------- Comments for file: twilight.f -------------------------------------------------------------------------------- The FORTRAN 77 code that generated Table 3 is given, where the user may specify another twilight coefficient and an exact CCD readout time. -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 27-Feb-1995