[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Quantifiying Flat-Field Results



Glenn Gombert wrote:
>

> 
>         Chris made the comment:
> <snip>
> "Another thing. is the purpose of a flat.  If there is truely a
> gradient in the sky, then application of even an ideal flat
> should +NOT+ remove the gradient from the image."
> 
>         Is interesting to note that the purpose of the flat-field (in part)
> *is* to correct for gradients and any other "systematic errors" that are
> introduced in the image by the sky, dust on the ccd camera, vigneting of the
> lens, etc so that these variations will not influence the photometric
> measurements.
>
 
This is going to be a good debate.  I don't think I would change my
above comment.  Glenn seems pretty sure too. 

This I agree with:
"        Is interesting to note that the purpose of the flat-field (in
part)
> *is* to correct for gradients and any other "systematic errors" that are
> introduced in the image by XXXXXX, dust on the ccd camera, vigneting of the
> lens, etc so that these variations will not influence the photometric
> measurements."

I only Xed out two words "the sky".  IMO a "flat" characterizes +only+
the instrument.  Yes this includes dust, filters, vigneting, variation
in gain between pixels and so on.  One should be able to apply the flat
to any image as long as the hardware did not change.

-- 

--Chris Albertson

  chris@topdog.logicon.com                Voice:  818-351-0089  X127
  Logicon RDA, Pasadena California          Fax:  818-351-0699