Night Sky Flats - again..

bodon

Im intrigued with these flats after watching the video again.  So I need to pick your guru brain as mine is like a light bulb.

I noticed that the different areas of the sky for the flats were done in only one filter, plus at a different exposure time to the light frames.  How far should one go with exposure zenith times subs compared to; if my target subs are at say four or five mintutes ea?

The photo turned out after stacking so the time did not obviously matter?  Is there a requirement when using this technique to take those zenith area/subs with all the filters I would be using; say with NB and BB or is one type of filter ok?   Just cant get my head around that the norm is to take a flat for each type of filter when using a panel to get that same modelling as the filters as such but not in this video.

Appreciate your time Ta

We need to see a video on your remote setup....

BlockHead

Exposure times for flats are not correlated with light frames. The idea behind flats is to get enough illumination. With night sky flats... you are trying to capture the sky itself. So the exposures are long compared to panel flats. So target sub times do not matter. 

Yes regarding the zenith through all filters. All filters of course is necessary since the flats are per filter. The Zenith is a very good choice since it will likely be free of gradients at the zenith. Having any gradients in your night sky flats is a disaster. 

Night sky flats unfortunately are not good for narrowband. This is because the sky/background is too dark through these filters. You cannot mix and match flats from different filters. 

In the video I certainly do not intend to apply flats of a different color to the target data. If I did make this mistake...it is exactly that. You always match filters for flats and light/target frames.

-the Blockhead

bodon

Thanks for that clarification.  Ta