From: Alan Friedman <alan@greatarrow.com>

Date: December 6, 2007 8:07:24 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] The sharpness curve

Hi Duane,

From time to time I will get an uncharacteristic Sharpness histogram when stacking. This can take a number of forms, but in general I think it indicates that Astro IIDC is having a hard time with the data. One of the causes can be too much noise - perhaps from a high gain settting. Seeing aberrations come in a variety of shapes and sizes and sometimes this data can be averaged with good result despite the high noise level in the individual frames. But it might require hand selection of frames. Version 4.0 of Astro IIDC (currently in beta testing) enables this option. 

I believe that Milton has posted in the past what the different curve shapes  in the CI plot indicate - perhaps he will add more detail on this.

Sorry you didn't have better seeing last night. I decided to sleep through it, which should have helped ensure a good night - but I guess not this time around... ;^)

Alan

On Dec 6, 2007, at 2:28 AM, Duane wrote:

Just got in from a session. That 300mb chart said it would be pretty stable tonight... NOT!

Oh well, I took some shots and froze my fingers off. It was -4 F and I'm just glad all the
equipment worked.

Tonight's session leads me to a question. I always have AIIDC set to show me the graph
after it determines sharpness. Most of the time this chart looks like a standard bell curve
with room on either side. I've had it do other things (rarely) like put a block of images on
the far left and a stream of images running off to the right, dribbling off at the end. This
was a night of better seeing.

In any case, does this graph ever give a hint as to how good the seeing was by its shape
and is there an ideal place to make the selection (% vs. #) of images to stack (such as, right
where the images drop off dramatically or where there is a little plateau on the sharp side
of the bell curve, or where there happens to be a large spike in numbers on the sharp
side)?

Please let me know if you don't understand the question.

Thanks,

Duane

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