Taking Flats

[leon]

Hi Guys, well i do know how to take flats, but is there a level of consistency in the final product, and when is the best time to take them if not using a light box.

With consistency i mean is there a certain shade of grey, or for that matter a certain shade of anything.

Last night i took three sets, first i waited for the sun to just set and covered the scope with a white material cover that i made, that set came out mid tone grey.
The next set was about 15 minutes after sunset, they came out quite dark grey.
And finally the next set i took well after sunset,with no white cover at all, and they came out a medium bright blue.

I presume blue is no good, but what is acceptable in the tonal rang of grey's, and when is the best time.

Thank You for your comments in advance.

Leon

[bloodhound31]

Hey Leon, don't you hate it when you get all those views and no reply?

As far as I have read in so many tutorials, just a white T-shirt stretched smooth over your objective and evenly lit should do the trick.

I am thinking of using the t-shirt in conjunction with a 100 watt light globe shining on it from a couple of feet away.

I haven't used flats in any of my astrophotos yet, so I don't know what kind of improvement it will make yet.

Hope this some help mate.

Cheers.

[Alchemy (Clive)]

i quote from a text book "aip 4 win"

Ideally the raw flat exposure should fill the charge wells in the ccd photosites to roughly 1/2 of their full depth, enough to produce a strong signal but not so close to saturation that the ccds response to light becomes non linear.

to make a master flat feild frame of extremely high quality , shoot at least 16 raw flat field frames and 16 flat darks . to make the master average the flats average the flat darks , then subtract the averaged flat dark from the average flat field..........................


i know ... so you want to know what a flat dark is.....thats the dark frame plus bias for the flat exposure ... confused .... yeah it gets all technical 580 pages of it



for you blue frames just turn them into greyscale ???


happy picture taking

[EzyStyles (Eric)]

my flats are blue not grey at all. maybe due to the fact that im using a modded dslr? this works quite well as for me when subtracting flat frames with my lights frames. my lights are bluish . set the cam to av mode at iso100.

[EzyStyles (Eric)]

heres an example. also tested with and without the UHC-S filter. same colour.

[edwardsdj (Doug)]

I have no experience in this but am keen to get into it

There is an awesome article on IceInSpace including the issues you refer to at http://www.iceinspace.com.au/index.p...63,211,0,0,1,0

Take care,
Doug