[fitsbits] exposure time - resolution

[Arnold Rots]

To answer rge first question: I would expect it to refer to the
resolution of the _data_, not the instrument - and hence the
convolution of the instrumental resolution and the binning.

The nice thing is that one can distinguish between integration and
sampling, depending on whether the resolution is greater or less than
the pixel size.

But there are two major problems:

1. The shape of the resolution function is not specified, and the
Gaussian assumption is shaky, as you argue below.

2. The implication is that the resolution can be characterized by a
single number.  This is in general an invalid assumption since the PSF
tends to vary over the FOV - dramatically for X-ray mirrors, but even
for radio images.

  - Arnold

Steve Allen wrote:
> 
> On Mon 2000-06-05T12:01:36 -0700, Tom Kuiper hath writ:
> > looking for a keyword that apparently doesn't exist, but could be named
> > something like CRESLx, which would be the full width at half maximum
> > of the instrumetal response along the coordinate x.
> 
> What meaning should be used if the resolution of the instrument is
> much smaller than one pixel; i.e., the pixels are huge?
> This could be relevant in situations of low S/N where binning of
> a CCD is done on the chip during readout.
> 
> In such a case the resolution in the FITS file has a bin-like profile
> that doesn't match the Gaussian-like FWHM notion.
> 
> In the more general case of binning during data processing, how
> should such a keyword be redefined if the binning is done
> 	by averaging pixels?
> 	by sampling pixels?
> 
> --
> Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
> sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
> PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93
> 

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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 81                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head-cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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