[vsnet-chat 861] Re: PSF-fitting or aperture photometry (Richmond)

[Taichi Kato <tkato>]

> 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?

    We sometimes use this "out-of-focus" method for precise photometry
of bright stars.  However, this method necessarily decrease the S/N
for faint stars.  Choice depends on the targets and instruments.

    This method doesn't usually help PSF photometry, since many of PSF
photometry packages are optimized for Gaussian-like PSFs.  Defocused
PSFs are usually non-ideal for simple mathamtical functions.

Regards,
Taichi Kato

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