8 replies to this topic

[jackmday]

I am having trouble with my Rokinon 24mm + Canon 80D--the stars always look distorted. I am pretty sure it isn't because of drift or the mount because the distortion is the same size regardless of exposure length.

 

The pictures here are the bottom right and bottom left corners of a 30s exposure. It seems like the tails point towards the center of the image, which would suggest coma, right?

 

And I am pretty much screwed if it is coma, right? There's no fix?

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[Tapio]

Yep, stars are tough targets for camera optics. In daylight images it's harder to see imperfections.

You could make it somewhat better by using slower f stop.

[jackmday]

Yep, stars are tough targets for camera optics. In daylight images it's harder to see imperfections.

You could make it somewhat better by using slower f stop.

This comes from the lens though, right? Not the camera? 

[Tapio]

This comes from the lens though, right? Not the camera? 

Yes, the lens.
 

[sharkmelley]

Does it happen in the top corners of the image as well?

[BrianThePrimate]

Yeah, star bloat. Try stopping your lens down once or twice instead of using it wide open, you often get sharper stars that way with a camera lens. Not sure if that will help, but that is my experience.

[mayhem13]

Is this tracking or stationary?……

At 24mm focal length Ron APS C, your image will be grossly under sampled anyways…….which is quite OK for wide field landscape AP. 
 

There’s known inconsistencies in this lens too with good examples and duds…..but if this is an un tracked frame, 30 seconds is too long.

[smiller]

Looks like coma.  If the little comets are pointing towards the center from all four corners, then it’s the classic coma symptom.

[lurking_grue]

I agree with the others who suggest adjusting your F-Stop.  If you were W/O at 1.4, drop to 2 or 2.8?  There may be others who know this lens better and if it has a 'happy' spot - which is really just saying the best compromise.