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Problem focusing in stars- Lens problem?

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Hello All,


I'm an amateur in Astrophotography. After a long research between rokinon 14mm f2.8 vs Irix 15mm f2.4, I just made my first investment in buying an astrophotography budget lens (Irix 15mm f2.4 firefly) since it is good at landscape photography too.


Coming to the problem, I used the lens with infinity settings to take milkyway photography. but the stars are not sharp. Later I manually zoomed and used live focus to focus in the star and tried the best to make it appear sharp. I still get the stars sharp at one end and distorted at the other end. the lens cannot be focused for a round star appearance at all. 


I tried this with my canon wide angle lens, and I can get a sharp star focused.


I have attached the images. What could be the problem? is the fault with my new lens? Should I change it? or is it something else?


please help to identify the problem. 


Links to the images:


(images are zoomed to  100% to show the problem). 

Edited by Pavithra balu
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Hi Pavithra wlecome to the forum.

It looks like that lens is not suitable for astrophotography from the pictures you have posted. It does appear to have a lot of elements in the optical train (15 according to their website) so any one of those could be misaligned. Probably fine for landscape work.

The Rokinon lenses seem to be better for astrophotography but I have nor seen any reviews of the 14mm f2.8 one. The 135 is the one everybody raves about.

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