Re: Field Rotation


M Hambrick
 

Hi Brian

I am not sure what to think. As near as I can tell, the total drift that I measured over the 5 hour continuously guided session was constant. If I assume this to be the case, then I think I am correct to conclude there was also drift occurring while I was taking my images which could result in elongated stars.

I measured 7.91" drift in RA and 25.5" in Declination over the 5 hours (304 minutes) of imaging. This calculates to an average drift rate of 0.026" per minute in RA and 0.084" per minute in Declination. For a 10-minute image this would be a drift of 0.026" in RA and 0.83" in Dec. Keep in mind that this RA drift rate is in seconds of RA. To convert to seconds of degrees you have to multiply this number by 15.

Is my system sensitive enough for this to show up as elongated stars ? I don't know. Many of my images contain very slightly elongated stars across the image. Is this due to drift ? The image scale with my scope / camera combination is 1.04" per pixel. On this particular night, the best focus I was able to get was a FWHM between 2" and 2.5".

Mike

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