CCD vs Film? Lots of time vs no patience? Alright, this is your place to discuss all the astrophotography what's and what's not. You can discuss about techniques, accessories, cameras, whatever....just make sure you also post some nice photos here too!
I obtained my Flats with the 'White T-shirt trick' in daylight. Simply cover the scope's obj with a white cloth or T-shirt and point it up the sky. Search for a patch of sky that is overcast to provide even illumination.
I can't do that as I need to took apart my equipment for transportation back and I won't be able to put everything back at the same orientation and focal distance for the flat to be useful. So the light pollution flat is the best I can get.. ha ha ha
Have a nice day.
Yang Weixing "The universe is composed mainly of hydrogen and ignorance."
Ya... it's a bit boring doing nothing while waiting 45 minutes for DSLR to capture the series of images and later another 30 minutes for the flat... But will get excited by thinking that I might get a nice image May be will learn constellation next time while waiting... ha ha ha
wow....nice Weixing really good job 8-) 8-) I can be your imaging companion just too fill the boring 45 min of waiting..... too bad even on my off day also need too come back to work to settle urgent things to do....will be your companion again if no more busy period.....
thing to note: flats are advisable to be taken best right after the imaging session where possible. like what weixing has pointed out, it is important to have the exact same orientation of the imaging camera, and filters. Just a little off, even by a bit, if you have dust motes anywhere in the light path, it will not be effectively eradicated upon subsequent subtraction. I use a t-shirt method too, but towards a white wall in the balcony after every imaging session. Last time, I tried to take using twilight flats method, but due to the sensitivity of the ccd chip, it somehow manages to record stars even then. Nevertheless, to the purist, the best method will still be a lightbox as Vincent has pointed out, but to have one usable for many tubes is a daunting task. Commercial ones are unjustifiably expensive too, for now. The exposure duration of flats are also important to effectively generate a desirable light frame histogram profile...normally 30-45% of the peak dynamic range will do.
"The universe is composed mainly of hydrogen and ignorance." 
