|
Flats should be taken at the lowest native ISO setting of your camera.
The flats aren't contributing to your data -- they are used to correct for optical train aberrations.
The exposure duration will depend on the luminosity of your flat light source. Try to aim for an exposure that sits somewhere between half-way to two-thirds across the X-axis of the histogram. That should give you sufficient signal to work with.
Take 16-25 of them. Then, put the cover on your lens or telescope, and, take the exact same duration flat dark frames. Again, 16-25 of them. Median combine the flat dark frames into a flat master dark frame. You then use this flat master dark frame to calibrate your flat light frames. Median combine them, too.
H
|