Deep Sky Galaxy

…and the Whale again

I’m beginning to feel some understanding with Captain Ahab and his obsessive tendency towards Cetacea. This has been rather a mission this spring and with weather keeping the imaging sessions short I’ve had to keep returning whenever possible.

The last two sessions I’ve experimented with increasing the subframe exposure time to 20 minutes. This has some major benefits in increasing the signal to noise ratio with some downsides in increasing bright star saturation and reducing the number of exposures to stack. Some further improvements may be gained by going to 30 minutes but, having shot 9 hours worth of 20 minute dark frames the other night I may as well get some use out of them. A darker sky may be required as the exposure length increases.

To incorporate the new exposures in the existing stack I’ve simply calibrated them and then scaled by 50% using PixelMath to match the existing 10 minute subframes.

I’ve worked rather harder in Pixinsight to retain star colour while, at the same time reducing the colour noise in the background. Star masks are invaluable in this and they’re really easy to create using Pixinsight.

This marks the end of data collection on this target for the year as it’s now past culmination by the end of astronomical twilight and the nights are getting shorter. Total time on this is now about 8 hours.


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