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Rokinon 14mm Focus Issue

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#1 dwyer2bp

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Posted 23 June 2021 - 09:30 PM

Hello all,

 

I recently picked up a brand new Rokinon 14mm lens (Canon mount). I connected this to my ASI294MC-Pro via ZWO's canon adapter which gives me the correct spacing for using EF lenses. I can't reach focus! The focus ring stops at the infinity symbol with fat stars and there is clearly nothing more I can do.

 

Does anyone have any experience like this? Here is the lens I just picked up. Also, with the ZWO camera adapter I made sure the 5mm ring is not installed (which is for 12.5mm back focus cameras). The ASI294MC-Pro is a 17.5mm back-focus. I can try to connect my DSLR directly to the lens but I believe I will see the same results.

 

https://www.amazon.c...n_title_o03_s00

 

Did I buy the wrong lens?

 

Thanks!



#2 dwyer2bp

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Posted 23 June 2021 - 09:36 PM

By the way, I am judging things with a bright star in the center of the FOV. I see horrible coma (granted out of focus) halfway from center. I also have a optolong l'pro filter inside the zwo-canon adapter.

 

just more info.



#3 RogerM

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Posted 23 June 2021 - 09:41 PM

Are you running the lens wide open?  If so, close down the aperture at least a couple stops.



#4 dwyer2bp

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Posted 23 June 2021 - 09:56 PM

I did try other apertures and still no good focus. I did disconnect the lens and slowly pull it out and noticed focus was acheived. I added a 5mm spacer but that was too much..going to try a few small spacers and see what happens.



#5 Dynan

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Posted 23 June 2021 - 09:58 PM

I just today returned an EF to 42mm adapters to Mr. Bezos because it wouldn't reach focus at infinity. Seem to be a problem with the lens/adapter combination. There might be adapters that work, but they are probably expensive...like hundreds of $$$. But I may be wrong on the latter point.



#6 dwyer2bp

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Posted 23 June 2021 - 10:06 PM

Well I did add a 1mm spacer between the adapter and my camera and now can achieve focus. What a nightmare (at least the feeling).

 

Sort of disappointed but who knows, maybe it's because I added a filter in between the lens and the sensor which required an additional spacing to compensate.



#7 Jim Waters

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Posted 23 June 2021 - 10:12 PM

There's a YouTube video on how to adjust the inner working of Rokinon lenses for infinity focus.  Do a search.

 

Consider returning the lens.



#8 Jim Waters

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Posted 23 June 2021 - 10:34 PM

FYI 

https://www.youtube....h?v=gtt9bcJDU2U

 

Also

https://www.cloudyni...inon-14mm-lens/


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#9 dwyer2bp

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Posted 23 June 2021 - 10:43 PM

Well thanks for the suggestions. I have found troves of topics on adjusting the infinity stops on these lenses. If it does not reach focus with my DSLR then I'll either return it or try the adjustment.

 

Thanks again everyone! The coma still is a bit disappointing on this lens even at F/8.0. F/2.8 is pretty awful (coma).

 

Clouds have rolled in and I'm packing it up.


Edited by dwyer2bp, 23 June 2021 - 10:43 PM.


#10 Jim Waters

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Posted 23 June 2021 - 11:12 PM

I had a 14mm and returned it the B&H Photo.  The lens wasn't usable because of coma and other distortions.



#11 dwyer2bp

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Posted 23 June 2021 - 11:29 PM

I had a 14mm and returned it the B&H Photo.  The lens wasn't usable because of coma and other distortions.

Yea the coma is very bad on this lens. I also just tried my DSLR and it would not achieve focus either. So good bye Rokinon lenses...sad I was excited but at least Amazon shouldn't give me any guff about returning them.




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