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It is straightforward to take twilight flats against a cloud-free sky using filters. I do this essentially every clear night with a Sloan u filter. It is best to point the telescope near the zero-gradient 'Chromey spot', which is roughly 15 deg off the zenith along an azimuth opposite the Sun. This time of year, this is at a Declination somewhat north of your latitude. Just doing it at the zenith may be good enough with small telescope fields. With an f/8 system I start the u flats at about Sun elevation -2 deg, but you will have to experiment with this. In any case, it will be quite a bit earlier than one would do twilight flats in B and V filters (say).
It is straightforward to take twilight flats against a cloud-free sky using filters. I do this essentially every clear night with a Sloan u filter. It is best to point the telescope near the zero-gradient 'Chromey spot', which is roughly 15 deg off the zenith along an azimuth opposite the Sun. This time of year, this is at a Declination somewhat north of your latitude. Just doing it at the zenith may be good enough with small telescope fields. With an f/8 system I start the u flats at about Sun elevation -2 deg, but you will have to experiment with this. In any case, it will be quite a bit earlier than one would do twilight flats in B and V filters (say).
\Brian
Steve