Messier55 is a globular cluster located in constellation Sagittarius. This cluster is very difficult to photograph from central Europe, because there is located not far from horizon. For example Charles Messier hat troubles to locate this cluster and it took him 14 years to spot it. I made a trip to Gavdos – the southernmost place is Europe. There the cluster was significantly upper in the sky.
M55 is 17600 light-year far from the Solar system, it has approximately 100 light-year diameter and contain 100 000 stars.
Techanical details
Telescope: | RC 154/1370 |
Aperture: | 154 mm |
Focal length: | 917 mm |
Mount | iOptron CEM25P |
Autoguiding | QHYCCD miniGuideScope 130 mm f/4.3, ZWO 174 MM |
Camera: | ZWO 1600 MC @ -15C |
Corrector: | Astro Physics CCDT67 |
Filters: | UV, IR cut |
Exposure: | 37x 120s Gain 240 |
Date: | 2017-09-29 |
Hello, great pic, truly. But I have a question : did you crop the original ? Because the corners look surprisingly sharp.
Hi, it’s cropped, but very little, ~10-15 pixels on each side. The sensor of ASI 1600 is micro 4/3 18×13 mm, which is not that large. Moreover the focal length 920 mm makes the field of view quite small. The corrector/reduced AP CCDT67 can correct only sensors of size like that. I tried with APS-C sensor and the stars in the corners were quite deformed.
I captured this cluster with shorter focal length (630 mm) and better corrector, which can cover whole APS/C sensor here:
Jakub