From: Antonio Agnesi <antoniangelo.agnesi@gmail.com>

Date: February 15, 2010 8:29:00 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] about focus and seeing...

Thanks Alan,

using a "space view" calibration reference is a clever idea, at least for final tweaking! Personally I find the RGB alignment using layers in Photoshop to be quite boring, slow and not very accurate (the blue level is generally fainter, unless one change CCD exposure as you do), so I wrote a short Matlab script to automatically generate aligned and cropped frames of the same size, each normalized with the same maximum pixel intensity (this is like changing exposure to achieve similar hystograms, more or less). This ensures fast and precise final (L) RGB synthesis from pre-aligned (L) R, G, B with Astro IIDC, Nebulosity or any other program used for ccd image processing.

I too don't like collimating the scope if it is unnecessary: indeed I only check if it is collimated, but I have not needed to tweak it after I got it and recollimated six months ago. Since I use this scope mostly at home I do not expect frequent recollimation! You answered clearly to my concern: it may be that the "dancing" star diffraction pattern does not tell the truth, indeed I noted the sharpness difference of the IR R G B channels definitely accentuated with poor seeing, and it will pay more attention to this "indicator" the next time.

Antonio

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