Start NGC 891

I started a new imaging portrait, with about 90 minutes of data capture before the almost-full moon rose and lit up the sky.  This is 16 300-second subframes of NGC 891, calibrated with darks and flats, luminance only, stacked and processed in CCDStack.

On the next few clear nights I’ll add more luminance data and colour.  This image is cropped – about the inner 75% of the full frame – to eliminate distortion I’m getting around the edges.

This was my first “real” use of the mount, as opposed to testing and calibration, since all the refurb work.  It’s performing quite well.  Despite the testing suggesting unguided imaging at 300 seconds would be fine, I used guiding – why not, and for practice.  Seeing was poor – about 2 arcseconds of jitter, so I took longish guide exposures (5 seconds) to average out the seeing and avoid having the guider chase it around.Guiding corrections were within +/- 1 pixel, which is 1.05 arcseconds on the guide camera, and usually within +/- 0.5 pixels, or .5 arcseconds – consistent with seeing scintillation of 2-3 arcseconds.  The large spikes in guiding are artificial – that’s the software deliberately throwing the guide position off by 3 pixels after each subframe, then letting the guider drag it back in line, to create subframe dithering.

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