M13 – The Great Globular Cluster in Hercules

Friday night finally brought clear skies to me, but it also brought a bright moon at around 82% luminosity. Because of this and also because I do not have any clear view points on any bright nebula, I decided to do something different. We are currently in what is called “Galaxy Season” in the Northern Hemisphere – a time when a lot of popular nebula are below our horizon or rising really late / early in the morning. For reference, I can now begin shooting the Cygnus regions around 2:30am. Since I had a bright moon and because of my current focal lengths (380mm / 480mm depending on my flattener) I decided to do something other then galaxies – globular clusters.

I had never shot a globular cluster before, and with my focal length coupled with the bright moon and my bortle 8 skies, it presented a challenge. I have been using the L-Pro filter by Optolong for my broadband targets, but I have had issues with achieving good focus consistently as well as light transmission. I am under a firm belief now that my best bet in shooting targets like this, and even galaxies, should be done with no filter at all.

I began the night shooting M3, a globular cluster in Canes Venatici, and then moved to M13 once it had risen above the tree line. On both targets I was able to get right at a hour and a half of integration time. My initial processing of M13 had me blowing out the core really bad so I went back and made some adjustments, mainly in how I did the curves in Photoshop. I posted the images on Instagram but I was still not totally happy with my result. I went back and started from scratch to get my current result. With my focal length, bright moon and light pollution, I am happy with the results.

60 x 90s
20 darks; 50 flats, dark flats and biases
400 ISO – Bortle 8 – Lunar Luminosity 82%

Meade Series 6000 80mm Triplet APO
Canon EOS Ra
Ho-Tech Field Flattener
No Filter

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