[Aavso-photometry] FWHM, up to where?

[Yenal Ogmen]

Hi all,

I just want to ask you about your experiences of different FWHM. Generally, I have 3-4arcsec FWHM at my site. I usually arrange my focus in such a way not to have FWHM less than 3arcsec. As far as I know, if you have very small FWHM, your loss of the star light can be big due to circumference of the pixels. Anyway, last night, there was breeze and the seeing was terrible. FWHM was around 5arcsec at the beginning of the time-series when the star was at its heighest position. When it was almost the end of the session, FWHM exceeds 8arcsecs. But when I did the photometry in the morning to get the LC of the eclipsing binary, I got pretty good LC.(http://www.lookatcyprus.com/astronomy/yenalogmen/TZBoo.jpg). My question is how do our observations affected due to FWHM? Of course, it is obvious that SNR decreases with the increase of FWHM but its not that much as far as see for the relatively bright stars. Is there any theorical boundaries for FWHM for precise
 observation? I just want to hear your FWHM choices and experiences you faced.

Thank you.

 
Yenal Ögmen
Green Island Observatory (B34)
www.greenislandobservatory.com
Geçitkale
North Cyprus