|
You don't say what equipment you are using so I will mention 4 ways that you could take flats.
You could use a Light Box and take them immediately after your Lights and Darks, you could use the twilight method, using a clear twilight sky, you shoot your flats before you image, you need to be reasonably quick as the sky darkens and also not image any stars or you could use daylight flats taken with a white T-Shirt over your objective. You can also shoot against a light coloured wall although I think this method could lead to uneven flats.
I use method 3, I have a refractor and DSLR and use a known setup and camera orientation, I shoot my flats usually in the afternoon with the telescope pointing away from the sun and into a blue sky, I try to keep my histogram towards the left and shoot about 20 or so around 400th to 600th of a second. You then stack the images together to make a Master Flat. I have three Master Flats taken at Prime Focus, With Reducer and with Extender on my Takahashi FS-102, I normally use mine for quite a long period before making new ones.
Cheers
JohnG
|