View Full Version here: : Fwhm. What values with your setup?

29-06-2012, 05:35 PM
I have been commisioning a 12.5 rc of late, and I would like to know what others are getting as a fwhm value with similar gear.

Or... Even if have gear that is not similar, post it anyway! I am especially interested in the gso rc's people are using.

I am getting fwhm's of around 3 with a stl6303 and aol with the rc, 10 minute subs.

I have a 150mm Barry Adcock built scope, and I can regularly get fwhm's of 1.8 at f9 ( with ap 2.7 tvph). Occasionally I get values as low as 1.5 with 5 minutes subs.


29-06-2012, 05:55 PM
I'm interested in this subject.
What units are you using for the FWHM measures?
I have a spreadsheet which we use in spectroscopy for calculating the FWHM (for the entrance slit gap) and also for the resolution of the spectroscope (the minimum is basically two camera pixels) SimSpec V4
I found the image size was very much dependent on exposure (ADU count) and had no relationship to the measured FWHM for brighter stars/ over exposed etc.

29-06-2012, 06:14 PM
I use maxim dl for measurement. The values I have given are a 'global' fwhm, rather than a localized fwhm.


29-06-2012, 06:18 PM
Measured in pixel??

29-06-2012, 07:05 PM
Yes, pixels.

29-06-2012, 07:57 PM
Where in maxim are your measuring that? In the stack process?

They're a lot better than what I get in maxim, but my figures in maxim are usually worse than what I get I'm CCD inspector.


29-06-2012, 08:44 PM
Dave, thanks for your comments.

I have been measuring in maxim, in the stack function. My buddy measures his fwhm in ccd inspector and is usually a lot better numbers from his similar rig. I thought it may be down to optics. I will do some experimenting with inspector and maxim. Food for thought.

Paul Haese
30-06-2012, 05:23 PM
Using an STL11K on my GSO RC12 I have obtained values as low as 1.20 per sub and as high as 3.34 (bad guiding on these images). Seeing is going to be the major influence.

01-07-2012, 09:32 PM
I use CCDInspector for measurement and it uses Arc Seconds as its units. With a QSI 683wsg-8 and a DSI RC10C I've never obtained better that 2.2, usually around 3.0 but has gone to over 4 some nights. It is nearly always due to atmospheric moisture here in TungKillo, SA.