[AZ-Observing] Re: FWHM measurements for Phoenix skies, anyone?
- From: "Matt" <mluttinen@xxxxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>
- Date: Mon, 21 May 2007 05:25:16 -0700
Tom, Brian,
Thanks for the input. I have read much regarding image scale and FWHM
measurements lately. I have discovered an interesting trend: Most experts
recommend calibrating the scope/camera system to deliver 1.5 to 2.5
arcsec/pixel BUT all of the best images out there seem to be taken at sub-1
arcsec, at least at longer (2000+mm) focal length. I am referring to
narrow-field work of mostly planetaries and galaxies.
That is, while theory suggests that a long FL scope be mated to a large, 13+
micron pixel size camera, no one actually does this. So all of the "hot"
astrophotographers oversample, often hitting the 0.5 arcsec/pixel range.
With today's small pixel cameras, this is actually easier to accomplish.
I am intrigued by the narrowband approach, which largely bypasses the
effects of LP, but I have not seen much of this done on galaxies. Hmm . . .
Matt
-----Original Message-----
From: az-observing-bounce@xxxxxxxxxxxxx
[mailto:az-observing-bounce@xxxxxxxxxxxxx] On Behalf Of Tom Polakis
Sent: Sunday, May 20, 2007 11:05 PM
To: az-observing@xxxxxxxxxxxxx
Subject: [AZ-Observing] Re: FWHM measurements for Phoenix skies, anyone?
Matt,
Back when I was imaging with my ST-7 and 13-inch in Tempe, I routinely had 2
to 3 arcsecond FWHM seeing, as reported by MaximDL. It is always good to
keep the scope at least 45 degrees above the horizon, so imaging objects
within a couple hours of the meridian is crucial. There have been many
words written about image scale. For what it's worth, my 13-inch delivered
1.2" per pixel at the chip.
I never set the CCD imager up at a remote site, but my experience with
visual planetary observing has been that our desert sites are no better, and
perhaps worse, with regard to seeing than my back yard.
If you are interested in Webcam imaging, however, you want that image scale
to be only several tenths of an arcsecond per pixel.
As for the definition of FWHM (full width at half maxium), there's an entry
in Wikipedia.
http://en.wikipedia.org/wiki/Full_width_at_half_maximum
Tom
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