Re: Bits and pieces

[Stupendous Man <richmond@a188-l009.rit.edu>]

  I wrote:

>  One can recreate the master dark
>  and flat from the raw images, but that will take several minutes.

  Tom asked:

> How do you get a master dark from the object images?  I have assumed that 
> you can only get flats from the object images???  Also you can't get a 
> light box flat from the data, and at least I have been convinced that there 
> are problems with a sky flat due to the gradient in the sky.  

  Sorry about that.  What I meant to say was:

     One can recreate the master dark
     and flat from ___a complete set of raw images, including darks
     and lightbox flats___.

  So if the darks and lightbox flats are not kept in the same place
as the raw sky images, it takes more time and effort to put them
all together for re-reduction.

  Tom is correct when he warns

> [there] are problems with a sky flat due to the gradient in the sky.

I agree that using sky flats is not a good idea.

                                             Michael