Fan shaped stars in images

[BakedVoodoo]

Hi!

New to imaging but have been having some success recently with Rho Opuichi. However, im having an odd issue...fan shaped stars.

Ive stopped down the lens, used a different one, same issue. Anyone have reason this could be happening? 

Gear: Canon T5 unmodded plugged into laptop, AzGti mount in Eq mode - wifi connected to laptop. Rho image was using a Nikkor 50mm 1.8 lens attached with an Urth adapater set at F4, Iso800, 60 sec exposure (13 used in stack). Lagoon image was using Aspherical 28-200, F5.6, iso1600, 30sec exposure.

[The Lazy Astronomer]

Looks to me like a case of coma. From https://www.lonelyspeck.com/a-practical-guide-to-lens-aberrations-and-the-lonely-speck-aberration-test/:

Comatic aberration or just “Coma” is named for its comet like shape for point light sources.

Coma occurs when light from a single source entering at the edge of the lens is not projected at the same size as light entering the center of the lens. For this reason it becomes more apparent on point sources of light at the edge of the frame and at low f/numbers. Coma is common on fast (large aperture or low f/number) lenses but can also be reduced by stopping the lens to a higher f/number. 

[BakedVoodoo]

I thought that also but would i still be getting Coma at f5.6 on a 35sec exposure?!?!  The 50mm nikkor i know is bad for it, but the 28-200 is an aspherical lens which i swore were better for that. 

[wxsatuser]

There are very few zoom lenses that can do better than that.

Just like scopes we need to spend an arm and leg to get a good one.

What is the zoom lens btw

Edited July 30, 2021 by wxsatuser

[alacant]

13 hours ago, BakedVoodoo said:

Nikkor 50mm 1.8

Hi

Try f8 or smaller?

Whilst not as good as telescopes, there are a few affordable lenses which do ok:

55mm

200mm 

adapter

HTH