Find FWHM: Pixel Values, Gaussian Curve, Standard Deviation

[bugra]

Hi,
I've been searching on google for minutes but couldn't find out a consistent way so far. I mean, it seems everybody has something to say about it :)

My data consists of pixel values (ADU's). I am writing a script to obtain fwhm of seeing disk.

By definition of the gaussian curve, i should only calculate the standart deviation of these values theni get fwhm=stdev*2.355 .
Am I correct?

Or should i obtain a gaussian fit then i calculate fwhm as its name suggests?

Thanks in advance,
bugra

 

[EnumaElish]

If you do it both ways, and the answers are different, what does that tell you about the fitting algorithm that you used?

 

[bugra]

for multiple sources on the same frame, should fwhm be same?

 

[chemisttree]

I would think the actual value of FWHM is less important than the rate of change near perfect focus.