Specifications

AUTOSTAR CCD PHOTOMETRY 15
17. Repeat Steps 1 - 16 for each additional set of data points
desired (for a time sequence, for instance).
Note: Unless changed, the image files will be stored in a folder
called Meade Images. Find it and make a shortcut to it and put the
shortcut folder icon on the desktop for easy use later.
2.5.2 Flat Frames
Flat Frames/Fields provide a calibration for the pixels of the CCD
chip, and are used to remove defects (bad pixels), uneveness in the
chip response, and shadows from dust particles on the optics. Flat
Field images are taken just like regular star images; except the
telescope front end is evenly illuminated with white light. There
are several ways to do this. See Appendix G for information on the
suggested design and construction of a Light Box for taking Flat
fields. A simple light box seems to work best. One set of flat fields
(stacked/combined) must be obtained through each filter.
Sky Flats can be used if taken at the right time, just after or before
sunset/sunrise. Aim the telescope near the zenith and turn off the
clock drive (otherwise you may have star images even when the
sky is still fairly bright). Because the sky brightness changes
rapidly during twilight, sky flats must be taken as quickly as
possible. Dome Flats are a second method, pointing the telescope
at an evenly illuminated panel on the inside of the telescope
enclosure.
Take as many Flat Field images per filter as practical (10 to 100 is
ideal). The brightness of the illumination and/or exposure time
may need to be adjusted to get good flats. Adjust the exposure time
and/or brightness for at least 10,000 counts on the Histogram but
less than 65,000 counts (for each filter).