Digital Astronomy – things to do when it is cloudy!

When using the PD camera you can get away with very short exposures, for example, I seldom use more than a total of 300-400 seconds. Compare this with the times used by Geoff, Damian, Rob, Ken etc! My mounts and drives simply aren’t accurate enough to go longer (Its still fun though!). When doing this, I use the noise reduction algorithms built into the camera. A consequence of this is that sometimes dark halos appear around bright stars, and this is particularly obvious when the stars are embedded in nebulosity as in the window-sill image of M42 I posted recently. I tend to regard this as a small price to pay for the relatively instant gratification I get from the PD! Anyway, it would be nice to reduce this effect, and while contemplating the cloud cover, I thought of a method (or “workflow” to use modern parlance) that might do this with GIMP.

So, here is the M42 original, followed by a “de-haloed” version. It hasn’t gone away, but the “haloing” is reduced. I might try this on some of my earlier images if the clouds persist!

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