Tag Archives: galaxy

Added Colour to NGC 4565

Here is the first round of adding colour data to the previous NGC 4565 image. Colour doesn’t come through my light-polluted sky very well – I could use a lot more time on the colour channels, but will have to wait until next year because there isn’t much time now between darkness and the target setting.


Exposure Luminance: 90 minutes (18 x 5 minutes)
Colour: 20 minutes (10 x 2) of each of Red, Green, Blue
Camera QSI583wsg, with Astrodon LRGB filters, running at -15°C
Image scale 0.69 arceconds/pixel (luminance), 1.38 (colour)
Telescope AT8RC
Mount Paramount MX+
Guiding Autoguided with Starlight XPress Lodestar
Processing 32 dark frames per sequence
32 flat frames per filter
Sigma-clip mean combination on the darks and flats
Sum-combination on the light frames


NGC 4565

Finally a couple of beautifully clear nights, not cold, and not busy with other things.  I started data gathering for NGC 4565.  This is 90 minutes of Luminance only (18 5-minute frames).  It’s still a bit noisy in my poor quality skies, so I plan to do another hour or so next clear night.  Haven’t gathered any colour yet.

NGC 4565

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.