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M92, NGC 6336 and NGC 6332
© D Elijah
Credit D Elijah

M92, NGC 6336 and NGC 6332

Date 24/03/2017. The Globular cluster (M92) was my final target of the night. I normally spend time imaging M13 (just to the south of M92). However, I decided to dedicate the rest of the nights imaging to this lovely little globular cluster. It is quite a dense cluster that consists of two types of star (either pink white or jade green), I tried different RGB colour balances to bring out this difference. Also, the small and faint galaxies NGC 6332 and NGC 6336 are viable in the top right (RA+, DEC+) and top middle of the image repectively.

Weather: The sky was clouding up near the end of the night. Seeing was good. Wind was still strong (9-12mph) and I lost quite a few frames because of vibrations. Temperature was about 3-5 degrees.

Optics and camera: Skywatcher Evostar 120 F/D=8.33 (Achromat) with a Baader UHCs filter (for removing light pollution). The camera was a IR-filter removed Canon 600D.

Settings: 28 x 3 minute lights, 50 darks from library, 50 flats taken recently and 50 bias frames. ISO 800.

Mount: Skywatcher AZ-EQ6 with extension pillar.

Processing: The Lights and calibrations frames were processed using Deep Sky Stacker. I set the star detection thresholds to values that caught about 30-40 stars. The final images were stretched in RGB and I then balanced the histograms to retain white balance. Luminance was tweaked to show faint stars. I also used Gimp to add a selective Gaussian blur over a 5 pixel range to blend the RGB noise.


D Elijah


© D Elijah
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Considering the conventional wisdom is that you can't do AP with a cheap and simple achromat these are very good. The UHC filter doubtless helps a lot...


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9 minutes ago, rl said:

Considering the conventional wisdom is that you can't do AP with a cheap and simple achromat these are very good. The UHC filter doubtless helps a lot...


Thanks RL,

The filter does help a lot with removing LP and the blue halos but tbh the scope doesn't really produce a huge amount of chromatic aberration, maybe I got a good example from Skywatcher. Also, the evostar has a nice flat field and no other serious optical aberrations. However, at F/D = 8.3, it is slow and building up a decent image takes time.

Dan :happy7:

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