Standard star selection guide

Here is the rough estimation for standard-star magnitude for which exposure time would be long enough to archive higher precision photometry (exposure time ~ 2 sec or more).

Note: The suitable magnitude, of course, depends on seeing, color of the star, filter used, and the CCD binning.

Imaging:

V=14.5 or fainter for 1X1 binning + V-I bands -> Exposure ~ 5 sec.

Spectroscopy:

V=10.5 mag or fainter for 2X3 binning + [300B+Y47] -> Exposure ~ 2-3 sec.