[vsnet-chat 903] Re: PSF-fitting or aperture photometry (Richmond)

[Tonny Vanmunster <tvanmuns@innet.be>]

At 18:14 30/04/98 +0900, you wrote:
> Do you think that maybe of some help, as regards the point above, to
> have the telescope a _bit_ out of focus, to have a larger FWHM?

I have a 10" f/6.3 SCT at CBA Belgium, which on some nights defocuses itself
during a CCD photometry session (due to temperature fluctuations). The
resulting 
"out-of-focus" images, which I process using PSF photometry, clearly show a
decreasing differential magnitude accuracy (decreasing S/N ratio). So, I would
certainly not recommend out-of-focus photometry in order to enlarge FWHM values.

In fact, I use the increasing FWHM values to let my software automatically
detect
the out-of-focus "syndrome" and to attempt correcting it by sending appropriate
signals to the autofocus motor.

BTW : those of you looking for a good DOS/Windows-based PSF photometry package :
I mainly use MIPS (from LE2IM), which has an old-fashioned user-interface
but does
the job adequately.


Best regards,
Tonny Vanmunster

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