Samyang 14mm f/2.4 quality issues

[BigRD]

Hi all, I've just bought a Samyang 14mm f/2.4 for my Nikon D5100 and am not happy with the results. I've already sent one back and now the replacement appears to be just as bad. As you can see in the sample there is quite a difference in quality. The images were taken at a fairly dark area, ISO400 for 30secs on a Star Adventurer. The crop is from the centre of the lens. Image quality only started to improve after stopping down to f/7.1. 

If the aberrations are this bad at wide open it would effectively be a useless lens. My kit 18-55 zoom gives far sharper stars across the aperture range. Am I expecting too much from the Samyang or should this one be winging its way back too?

I appreciate any advice

cheers

[Charic]

I dont image yet, but had an encounter some time back, and in order to get back to genuine quality I sourced some mint second hand lenses for my D5000  from Grays.
http://www.graysofwestminster.co.uk/index.php

[symmetal]

My Samyang 14mm gave images much the same as yours and as you say is useless for astro. It's fine for daytime photos and I'd had it several months so didn't bother trying to get it swapped. It seems to be pure luck as to whether you get a good one and I don't know what the ratio of good ones to bad is.

Alan 

[Shibby]

I have the 14mm f/2.8 for my Canon, so I just went and took a look at some recent images that I took (I think wide open, but there's no meta with the manual lens). I can see a bit of coma in the corners but the central stars are pin sharp.

There's clearly something not quite right with your lens - something is not in alignment, because even if there is aberration it should be centred in the centre of the frame. Perhaps, if you do send it back, then try the f/2.8.

[BigRD]

Thanks all.  I've decided to send it back.

There's obviously a problem across the whole field and apertures down to f/7.1 something internally is misaligned. Faults aside the colours at f/2.8 look great with this lens. Shame.