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Rokinon 135mm f/2.0 - keep or exchange?

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#1 DubbelDerp

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Posted 03 December 2019 - 11:12 AM

Hello all,

 

So after struggling with vintage prime lenses and the CA associated with them, I decided to spend the cash on a Rokinon 135mm f/2.0 prime lens. I got a chance to try it out last night, but after looking at some of the light frames today, I have some concerns about the quality of the particular lens I got, and am hoping for some more experienced feedback as to whether this one is a keeper for AP or if I should exchange it for a different one. Specifically, I think I'm seeing a tilt in the lens that when focusing at a star in the center, the left and right sides of the frame are out of focus in different directions on an APS-C sensor.

 

Here's a crop from the center of the frame with a Bahtinov mask...

center_mask.jpg

 

Left and right sides of the frame:

left_mask.jpg  right_mask.jpg

 

Center of the frame on M45:

center_m45.jpg

 

Left and right sides of the frame:

left_m45.jpg  right_m45.jpg

 

I'm not seeing much difference between the lens wide open and stopped down three stops in terms of what I think is OOF. I had the lens supported by the camera on my skyguider pro, so I suppose there could be flex from the weight of the lens causing a tilt. Would supporting only the lens with a collar be preferable, or should they both be supported on a rail? I did take a single frame at M31 right about at the zenith, and I did not see any noticeable difference in how the sides of the frame were out of focus, so I don't think I can entirely blame flexure of the camera body. How would you recommend mounting this lens on a camera tracker?

 

Any feedback would be greatly appreciated on what I should expect with this lens!



#2 Jim Waters

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Posted 03 December 2019 - 01:06 PM

The quality control on Rokinon lens is hit-or-miss.  Especially on lens 35mm and below.  I would send the lens back.



#3 tkottary

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Posted 03 December 2019 - 01:29 PM

This does not look right .

#4 Poochpa

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Posted 03 December 2019 - 03:06 PM

I think you have a bad one and would send it back. I had to do that with a Rokinon 16mm lens. I just acquired a used Rokinon 135mm. Here's the PI Aberration Inspector image of one of my initial test shots with the 135, using a Canon T4i, 60s, ISO 800. Not perfect, but not bad. Focus was a little off.

Mike

IMG_0871_AbInspect3xmosaic.jpg


Edited by Poochpa, 03 December 2019 - 03:21 PM.

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#5 DubbelDerp

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Posted 03 December 2019 - 04:02 PM

Thanks for the feedback.. It confirms what I was thinking, that this would be best sent back for another. I do like how this lens gulps down the photons, but the reason for getting it was to get away from poor performance at the edges of the frames, not to replace one set of issues with another. But for less than 90 minutes of integration time, this lens is pretty incredible! This is a center crop, but you can see some blobby stars on the left side of the frame. Hopefully the next one is better.

m45_135mm.jpg



#6 DubbelDerp

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Posted 03 December 2019 - 04:03 PM

I think you have a bad one and would send it back. I had to do that with a Rokinon 16mm lens. I just acquired a used Rokinon 135mm. Here's the PI Aberration Inspector image of one of my initial test shots with the 135, using a Canon T4i, 60s, ISO 800. Not perfect, but not bad. Focus was a little off.

Mike

attachicon.gif IMG_0871_AbInspect3xmosaic.jpg

Thanks for the visual reference! If mine had performed that well, I would have been happy indeed. Back it goes...



#7 Poochpa

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Posted 03 December 2019 - 05:00 PM

Thanks for the feedback.. It confirms what I was thinking, that this would be best sent back for another. I do like how this lens gulps down the photons, but the reason for getting it was to get away from poor performance at the edges of the frames, not to replace one set of issues with another. But for less than 90 minutes of integration time, this lens is pretty incredible! This is a center crop, but you can see some blobby stars on the left side of the frame. Hopefully the next one is better.

attachicon.gif m45_135mm.jpg

Nicely processed M45, despite the lens aberrations!

Mike



#8 Kevin_A

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Posted 03 December 2019 - 06:09 PM

the 135mm f2 lens is a very sharp lens and unfortunately it is a lens that you will love only when you get a non de-centerred sample. Fairly common to have one or 2 bad corners.... so send it back and try again as most of us who own them did. Use it at f2.8 as it is even better stepped down ever so slightly.


Edited by Kevin_A, 03 December 2019 - 06:11 PM.

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#9 DubbelDerp

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Posted 03 December 2019 - 06:10 PM

Nicely processed M45, despite the lens aberrations!

Mike

Thank you! I keep thinking I’ve pushed the background too high, but I just love seeing the billowy dust clouds start to appear. The fact that there’s even a hint of them after 90 minutes has me excited about getting a good copy of this lens. 



#10 DubbelDerp

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Posted 03 December 2019 - 06:15 PM

the 135mm f2 lens is a very sharp lens and unfortunately it is a lens that you will love only when you get a non de-centerred sample. Fairly common to have one or 2 bad corners.... so send it back and try again as most of us who own them did. Use it at f2.8 as it is even better stepped down ever so slightly.

Thanks, will do. I just wanted to double check that this was unacceptable before doing the exchange. Appreciate the feedback!



#11 Coconuts

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Posted 03 December 2019 - 10:05 PM

My third Samyang 135 mm f/2.0 lens was a keeper.  B&H is great in that regard.  But I'm not sure if the tilt issues I ran into on units 1 and 2 was due to improper build, or simply a delicate design, where differences in shipping trauma resulted in different performance.  If the latter is true, then transportation while in my hands could eventually degrade the performance of my good unit.

 

One other comment: at f/2, image degrading focal plane tilt can easily arise for objects off the zenith from the torque of this lens on your camera bayonet mount.  I prefer to rigidly mount the lens, and allow the lighter and shorter camera to hang off the rear of the lens.  Details on how to do this are in my CN post, here:

 

https://www.cloudyni...-camera-lenses/

 

Before you send the lens back, try imaging at the zenith...

 

All the best,

 

Kevin



#12 ChristopherBeere

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Posted 04 December 2019 - 07:45 AM

Definitely send that one back those stars are unnaceptably defocused at the edges


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#13 DubbelDerp

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Posted 04 December 2019 - 10:37 AM

My third Samyang 135 mm f/2.0 lens was a keeper.  B&H is great in that regard.  But I'm not sure if the tilt issues I ran into on units 1 and 2 was due to improper build, or simply a delicate design, where differences in shipping trauma resulted in different performance.  If the latter is true, then transportation while in my hands could eventually degrade the performance of my good unit.

 

One other comment: at f/2, image degrading focal plane tilt can easily arise for objects off the zenith from the torque of this lens on your camera bayonet mount.  I prefer to rigidly mount the lens, and allow the lighter and shorter camera to hang off the rear of the lens.  Details on how to do this are in my CN post, here:

 

https://www.cloudyni...-camera-lenses/

 

Before you send the lens back, try imaging at the zenith...

 

All the best,

 

Kevin

Thanks for that... I saw your thread previously but didn't find it in my 30-second search.

 

Here's a single shot of M31 near the zenith. I'm definitely seeing the same focus pattern. There's almost an in-focus band from about the 11 o'clock position to about 5 o'clock, with the stars progressively worse farther outwards. I think if I overlaid the single frame and the m45 stack, the pattern would be pretty much the same.

 

M31-singleframe.jpg



#14 DubbelDerp

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Posted 09 December 2019 - 02:23 PM

Well the replacement looks quite a bit better. I had some openings between the clouds and took a couple test shots the other night, and the corners look pretty good. However, this one won’t quite reach infinity focus. I can fix that, though. Normally I’d send it back, but considering the optics look ok and I’d hate to keep returning lenses and getting mediocre replacements, it should be easy enough to adjust. 

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#15 Kevin_A

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Posted 09 December 2019 - 06:54 PM

here is a 30 second single light frame, un-cropped iso 400, nikon d7200, Rokonon 135mm at f2.0 for comparison in the corners.

I sent back a few lenses before I was happy all the corner stars were of equal size.

The image quality is greatly reduced but should show the star sizes in all corners for comparison

30 sec sub Rokinon 135mm at f2.0 on APS-C Nikon D7200
 
Here is a detail crop that was processed to show vast detail of only 135mm... but not great job.
small

 


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#16 Scott Mitchell

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Posted 10 December 2019 - 06:02 PM

Well the replacement looks quite a bit better. I had some openings between the clouds and took a couple test shots the other night, and the corners look pretty good. However, this one won’t quite reach infinity focus. I can fix that, though. Normally I’d send it back, but considering the optics look ok and I’d hate to keep returning lenses and getting mediocre replacements, it should be easy enough to adjust. 

Out of curiosity, how are you going to approach fixing the focus? I have some old Leica lenses that come up just short of focus in my setup. So, I'd be curious if your solution is generalizable.


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#17 tbrozovich

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Posted 11 December 2019 - 09:59 AM

I have this same lens and shooting with the d5100. I am having issues as you can see in this image https://imgur.com/8SgdyCq. Do you think this is a lens issue? I am not 100% what to try. Some discussions have suggested covering the view finder.



#18 DubbelDerp

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Posted 11 December 2019 - 10:57 AM

Out of curiosity, how are you going to approach fixing the focus? I have some old Leica lenses that come up just short of focus in my setup. So, I'd be curious if your solution is generalizable.

Well I was going to follow the procedure in post #3 in this thread:

 https://www.cloudyni...inity-focus-6d/

 

But I took the lens out last night, focused on Deneb with a bahtinov mask, and found that it was perfectly in focus in the center of the frame. So I moved Deneb to each corner and took another photo, and found similar issues. So I'm not going to bother - this one will go back as well. Maybe the next one will be better. Third try is a charm?

 

I have taken apart a couple vintage Takumar lenses, and once you expose the mechanicals underneath the focus grip, they were pretty easy to adjust the infinity focus point. There's basically a hard stop on the non-rotating portion, and an adjustable ring or other feature on the rotating part to which the focus grip attaches. If you can find a way to partially disassemble the lens, it might be apparent how to adjust. Just take lots of notes and pictures of the disassembly process!


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#19 DubbelDerp

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Posted 11 December 2019 - 12:57 PM

On the plus side, I did find that the mounting ring that came with my AT60ED is the absolute perfect size for this lens... I'll probably contact Astronomics to see if they can sell the ring separately. Check it out! It fits like a glove.

 

IMG_8630.JPG


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#20 Scott Mitchell

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Posted 11 December 2019 - 06:07 PM

Thanks for the information about adjusting the focus. I need to just look into what the lens' value is on the used market to see if I'm just better off selling it at this point. I'd hate to break it if it actually has decent value.


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#21 OrionSword

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Posted 22 December 2019 - 10:45 AM

I got one last year used and it is not really useful for AP, so I will just use it for general photography.  Sounds like they have a poor ratio for quality.



#22 garret

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Posted 22 December 2019 - 11:56 AM

 

Sounds like they have a poor ratio for quality.

Unfortunately poor quality control and variation in optical performance is almost a selling point for Samyang and Rokinon.

A few years ago I sold my Canon 135mm F2.0 in favor of the Sigma 135mm, but Euro 1400.= is a lot of cash for a few wide field images of the sky each year... so not yet decided what to do.


Edited by garret, 22 December 2019 - 12:03 PM.

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#23 Traveler

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Posted 23 December 2019 - 12:55 AM

On the plus side, I did find that the mounting ring that came with my AT60ED is the absolute perfect size for this lens... I'll probably contact Astronomics to see if they can sell the ring separately. Check it out! It fits like a glove.

 

attachicon.gifIMG_8630.JPG

Nice find! Please let us know if this ring can be bought separately.

 

My Samyang 135mm F2.0 for Nikon behaves perfect. I have not the issues you have. So it seems there are good ones out there but is seems getting such is kind of lottery.

Bought it for 450 euro new (2 years ago at Konijnenberg)...almost 1K euro less than the Sigma.



#24 Poochpa

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Posted 23 December 2019 - 02:47 PM

On the plus side, I did find that the mounting ring that came with my AT60ED is the absolute perfect size for this lens... I'll probably contact Astronomics to see if they can sell the ring separately. Check it out! It fits like a glove.

 

attachicon.gifIMG_8630.JPG

 

 

Nice find! Please let us know if this ring can be bought separately.

 

****

It can't. I checked with Astronomics.

 



#25 DubbelDerp

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Posted 28 December 2019 - 12:06 PM

Well the third sample finally looks good - at least on my older canon t1i. On my newer old t3i, the stars in the upper right corner are out of focus. The other two samples also looked bad on my t1i, so I didn’t really look closely until this sample looked sharp on the other camera body.

 

I assume that this means the sensor is tilted? I purchased this camera used on the CN classifieds about a year ago, already modified. I don’t fault the seller at all, but am interested in whether my conclusion sounds correct, and if so, how to adjust it. 
 

To follow up on the scope ring, Astronomics also told me they were not able to sell it separately from the scope. They probably wouldn’t make much money on selling just the ring, so I can’t blame them for that at all. There’s a sigma ring that looks like it might work, so I might give that one a try.  




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