Messier 39 is an open cluster located in constellation Cygnus and it’s only 825 light-year away from Eartch. The cluster is visually located on the galactic plane of the Milky Way, therefore there are so many stars in the background.

I already captured M39 two years ago, but with different camera and different coma corrector. This time I used slightly bigger sensor and brand new corrector TS MaxField. This corrector should reduce the focal length by 5% and also due to the larger sensor I got bigger field of view compared to my previous picture. However, the corrector is not capable of eliminate the coma fully and in the corners are the stars elongated. I spent some time by adjusting the tilt, but this obviously didn’t solve the problem. This means that the only corrector which is capable of eliminating the comatic aberration fully is Explore Scientific HR CC.

Technical details:

TelescopeNewton 254/1000 mm
Aperture254 mm
Focal length950 mm
MountGemini G53f
AutoguidingZWO 174MM, TS 60/240 mm
CameraZWO 071 Pro @-20°C
CorrectorTS-Optics 2" 3-element MaxField
FiltersHutech IDAS LPS-D2
Exposure58x180s, Gain 94, bin 1x1,

Here is the analysis of the curvature by CCD Inspector. I already adjusted the tilt by integrated push-pull screws on ASI071, but there is still some room for improvements.