trouble with flats

[south west stew]

Hi All,

sorry if this is a silly question but how do people take there flats. i tried for about an hour last night but could not get what is described as a good one. all i got was an over exposed pic no dust or vinetting aroung the edge any help would be great 

thanks

stew

[Scott]

this is what I do, know idea if it's right but someone on sgl told me this and it seems to work (thanks whoever it was)

after imaging I leave it set up (exactly how it was. Focus,framing etc)

the next day, I point it at the sky away from the sun and put a clean white shirt double layer over the apeture and set the camera to av and iso to 100 and snap away. I do around 20-30.

on th histograph the peaks should be about 1/3 of the way from the left.

Hope this helps