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08-22-2022, 03:49 PM   #1
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IRIX15mm lens problem in focusing star/milkyway

I'm an amateur Astrophotographer. 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).
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.

Now I have decided to return this lens. But confused if I should buy irix again or rokinon14mm?

I have attached the 100% zoomed images of the photos I have taken from this lens. Is this a faulty lens? or can it be fixed with calibration?

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

https://ibb.co/nLrxqcR
https://ibb.co/P9vVmNZ

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08-22-2022, 05:49 PM   #2
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If you get sharp in one part of the image and not sharp in another, then you're probably dealing with a decentered lens and a bad copy. I'd suggest returning it as faulty and trying another one.
08-22-2022, 07:15 PM - 1 Like   #3
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QuoteOriginally posted by MarkJerling Quote
If you get sharp in one part of the image and not sharp in another, then you're probably dealing with a decentered lens and a bad copy. I'd suggest returning it as faulty and trying another one.
@ MarkJerling Thank you. I still have window to return this. so, I will return and buy a new one.

---------- Post added 08-22-22 at 07:20 PM ----------

QuoteOriginally posted by Michaelina2 Quote
Perhaps a Astromania Bahtinov Mask Focusing Mask might help...

https://youtu.be/lu4h6zKaumU?t=240

... works for me. (search Amazon for price and availability)... M
Michaelina2 Thank you. But in this case, it seems my lens itself is defective. But will try to use it in my future photography.
08-22-2022, 10:32 PM   #4
scc
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The stars are distorted everywhere in the field, the lens is defective.
However do not expect a new sound copy to give round and sharp stars in the corner with such lens.

08-23-2022, 02:36 AM - 1 Like   #5
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QuoteOriginally posted by scc Quote
However do not expect a new sound copy to give round and sharp stars in the corner with such lens.
Super wide angle lenses are particularly well known to have centering issues. I went through 4 copies of the sigma 8-16mm f/4.5-5.6* until I was sent a 5th copy, direct from Japan that was completely flawless.


*Through the contacts my optical engineer colleague had, I sent a letter to Sigma Japan along with lens test charts from my optics bench of each copy showing the optical faults. Apparently my criticism found its way to the heads of Sigma Japan and they responded by sending me a 5th copy of the 8-16mm directly from Japan, with a lens bench chart certifying the lenses performance and a letter from the head of Sigma optical thanking me for the quality of feedback and apologizing for the issues I had experienced.


With a response like that it is hard to place fault Sigma entirely, however the local Pentax distributor remains on my personal black list.
08-23-2022, 05:37 AM - 1 Like   #6
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Several astrophotographers i know prefer the Rokinon,
That sample image shows the lens is not assembled properly. If the stars were merely out of focus, they would be circular, not coma-like blobs. Coma is normal at the edges on many lenses, this is not normal or acceptable. Send it back. It's defective.
08-23-2022, 07:09 PM   #7
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QuoteOriginally posted by scc Quote
The stars are distorted everywhere in the field, the lens is defective.
However do not expect a new sound copy to give round and sharp stars in the corner with such lens.
Thank you. I have initiated the return and ordered for a new one.

08-23-2022, 07:12 PM   #8
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QuoteOriginally posted by Digitalis Quote
Super wide angle lenses are particularly well known to have centering issues. I went through 4 copies of the sigma 8-16mm f/4.5-5.6* until I was sent a 5th copy, direct from Japan that was completely flawless.


*Through the contacts my optical engineer colleague had, I sent a letter to Sigma Japan along with lens test charts from my optics bench of each copy showing the optical faults. Apparently my criticism found its way to the heads of Sigma Japan and they responded by sending me a 5th copy of the 8-16mm directly from Japan, with a lens bench chart certifying the lenses performance and a letter from the head of Sigma optical thanking me for the quality of feedback and apologizing for the issues I had experienced.


With a response like that it is hard to place fault Sigma entirely, however the local Pentax distributor remains on my personal black list.
Wow. Thank you. That was very helpful. Though I donít keep my hopes high, I wish I will get a good lens in the second order.
08-23-2022, 07:16 PM   #9
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QuoteOriginally posted by ProfessorBuzz Quote
Several astrophotographers i know prefer the Rokinon,
That sample image shows the lens is not assembled properly. If the stars were merely out of focus, they would be circular, not coma-like blobs. Coma is normal at the edges on many lenses, this is not normal or acceptable. Send it back. It's defective.
Thank you. Iím sending it back.
I saw some comments on how irix lens has less distortion at the corners than the Rokinon and made this purchase. Letís see if I get a good one next time. If not, Iíll go for rokinon.
08-23-2022, 07:52 PM   #10
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I occasionally get something similar on my Rokinon 14/2.8 at f/2.8 with bright stars. Correctly or incorrectly, I classify it more as blooming and not really coma because the fainter stars look fine. When I stop down to f/3.5 it goes away and the bright starts are perfectly round.

A good copy of the Rokinon/Samyang 14/2.8 will give you perfect points of light with some distortion in the corners using Astrotracer. I do not have the Irix, but I looked at lots of reviews and test shots and it looked like the Irix was comparable to the Samyang but not better. The infinity stop on the Irix is nice and it sounded like the Irix build quality was better.

I also rented the Pentax DFA 15-30. It is comparable to the Samyang 14/2.8 but not noticeably better for astro shots.

I had to adjust the infinity stop on my Rokinon 14/2.8 but now it works great. Wish I didnít get the corner distortion with Astrotracer, but that would require a tracking mountónot ready for that yet.
08-24-2022, 10:50 AM   #11
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QuoteOriginally posted by pavithrakb Quote
@ MarkJerling Thank you. I still have window to return this. so, I will return and buy a new one.

---------- Post added 08-22-22 at 07:20 PM ----------


Michaelina2 Thank you. But in this case, it seems my lens itself is defective. But will try to use it in my future photography.
I have had a couple of problems with Irix lenses, and I have found their customer service to be absolutely outstanding. They are by far the best company I've dealt with as to photographic gear. Their 15mm had a reputation for decentering a few years back, but I think they corrected whatever was causing that - maybe your lens is "new old stock". If you send it back to them, well, my experience is that when you get it back, you'll have a better lens than you could have bought "off the rack" because of the personal attention. And, if they can't fix it (the problem with one of the ones I'd bought), they will replace it right quick. I can't say enough about those lenses, I think they're terrific.
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