Any ideas what this is?

[Kaptain Klevtsov]

The funny bit next to the star that looks like it needs collimating a lot and focusing as well.

This is taken using a Nikon D50 DSLR at prime focus on a Skywatcher 200mm f/5 Newt. In line was a "Hb" filter which has a broad bandpass in reality.

ISO 400, 10 minutes, in camera noise reduction on, RAW (NEF) format.

The attachment is a 100% crop of the running man area for reference.

Collimation was OK, the expected coma seems to be centred on the middle of the image so that the brightest part of the stars close to the edges shows a "tail" away from the image centre.

Also, this is from the left side of the image, but on the right side of the image there is a bright star which shows the same effect, and the artifact is below and to the left exactly like these ones.

Other than the nasty bits which appear to be something to do with the two bright stars that they are close to, focus looks OK, tracking looks OK, so what gives?

Captain Chaos

[geppetto]

Just a guess but could it be a reflection off some surface or other?

[Kaptain Klevtsov]

I honestly don't know Phil.

Another pointer that I've just come across, it's something in the camera / filter / 1.25" assembly bit because it rotates with the camera. In some shots I've got the camera in the wrong orientation to pick up the running man, but the artifacts are in the same orientation to the rame.

Captain Chaos