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Rokinon 135mm f/2 - Bad Corners - Pinched/Focus/or Bad Copy

Astrophotography
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#1 cdhgamer

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Posted 25 January 2022 - 01:19 AM

Hi all,

 

I bought a Rokinon 135mm f/2 months ago, and never got a chance to test it until it was outside of its return window because of a car accident and bad skies, bawling.gif I'm just curious if anyone thinks this is something fixable on my end like pinched optics or wrong focusing distance, or if I got a lemon I'm stuck with. The center looks great out to the corners, but as I was hoping to use this lens for lots of mosaics, it kind of defeats the purpose. 

 

Photo is 60 seconds at f/2.8 through a green filter (all filters showed the same results) on an ASI1600mm, not even a full frame.

 

Thanks!

Attached Thumbnails

  • Rokinon135mmj.jpg

Edited by cdhgamer, 25 January 2022 - 01:21 AM.


#2 galacticinsomnia

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Posted 25 January 2022 - 02:05 AM

send it back.

 

looks pinched but could be focus too.  more testing..  but if you know how to shoot already and you are not satified, send it back.

 

Clear skies!!


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#3 TOMDEY

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Posted 25 January 2022 - 02:17 AM

General-use camera lenses are most often deficient for astronomy, except for some top-shelf outstanding exceptionals. Your angular field (diagonal corner to corner) is over 18o. It's possible that field rotation due to polar (mis)alignment, and/or differential flexure are contributing to what you see there. Might make sense to image a static scene or even a bright star with very short exposure time. Focus on star at center and image that same star center and all four corners. If the corners look aberrated but symmetrically --- then that is inherent to the lens design. At $500, a 135mm F/2 is an ~economy~ lens. Camera lenses are comproptimized for all conjugates and rarely perform well near the extrema of range, field or speed. So, decent infinity corners at F/2.8 is probably just asking too much. As you have probably already researched... the premium performers kick in at double the price and go up, even way up from there.    Tom


Edited by TOMDEY, 25 January 2022 - 02:23 AM.


#4 Kevin_A

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Posted 25 January 2022 - 11:05 AM

Send it back…. Period! Mine is way better!



#5 whwang

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Posted 25 January 2022 - 11:26 AM

The OP said that it is outside the return window already.  So returning it would be difficult (not entirely impossible though).

 

You can try to sell it to those who don't do astrophotography at a discount price.  A bad copy for astrophotographers can still be acceptable (or better than just being acceptable) to others.



#6 calypsob

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Posted 25 January 2022 - 03:52 PM

General-use camera lenses are most often deficient for astronomy, except for some top-shelf outstanding exceptionals. Your angular field (diagonal corner to corner) is over 18o. It's possible that field rotation due to polar (mis)alignment, and/or differential flexure are contributing to what you see there. Might make sense to image a static scene or even a bright star with very short exposure time. Focus on star at center and image that same star center and all four corners. If the corners look aberrated but symmetrically --- then that is inherent to the lens design. At $500, a 135mm F/2 is an ~economy~ lens. Camera lenses are comproptimized for all conjugates and rarely perform well near the extrema of range, field or speed. So, decent infinity corners at F/2.8 is probably just asking too much. As you have probably already researched... the premium performers kick in at double the price and go up, even way up from there.    Tom

You clearly do not know the reputation of this lens.



#7 calypsob

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Posted 25 January 2022 - 03:56 PM

Hi all,

 

I bought a Rokinon 135mm f/2 months ago, and never got a chance to test it until it was outside of its return window because of a car accident and bad skies, bawling.gif I'm just curious if anyone thinks this is something fixable on my end like pinched optics or wrong focusing distance, or if I got a lemon I'm stuck with. The center looks great out to the corners, but as I was hoping to use this lens for lots of mosaics, it kind of defeats the purpose. 

 

Photo is 60 seconds at f/2.8 through a green filter (all filters showed the same results) on an ASI1600mm, not even a full frame.

 

Thanks!

I’m sure these poor companies that distribute these lenses are getting pulverized by people who shoot from the hip and immediately say you have a bad copy of the lens. This honestly has to stop.

 

If you are an imager you need to take the time to break down all of the points of fault before you make the final decision to send back the lens. The Zwo ef adapter is terrible. It has a ton of flexure which will reveal itself at F2.

Also you cannot just let the lens dangle from the bayonet or you will have flexure.

you also need to determine if you have sensor tilt. 
At F2 all of these things are critical.

 

It’s starting to become frustrating to see how much bad advice is so readily offered.

please for the sake of these small businesses that sell camera equipment, do your due diligence before you send something back.


Edited by calypsob, 25 January 2022 - 09:07 PM.

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#8 TOMDEY

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Posted 25 January 2022 - 04:39 PM

You clearly do not know the reputation of this lens.

As a great man once said, "Trust, but verify".

 

It takes only one lemon to destroy an otherwise impeccable reputation. Which is why I counseled cdh to perform other discriminatory tests before kicking it out of bed. If it turns out to be deficient as built --- then its reputation would justly wind up in the scrap heap, right along with uncountable ~also rans~. Most likely he has something else going on causing the problem, but a bad lens cannot be entirely ruled out based on reputation alone. At work we tested all incoming lenses... and found clinkers among the premiums. Our contracted quantities were so large that the manufacturers took the (very few) failures back for credit [what they did with them from there... we didn't care... imagined they went to individual singleton buyers?!]     Tom



#9 cdhgamer

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Posted 25 January 2022 - 06:55 PM

I’m sure these poor companies that distribute these lenses are getting pulverized by people who shoot from the hip and immediately say you have a bad copy of the lens. This honestly has to stop.

If you are an imager you need to take the time to break down all of the points of fault before you make the final decision to send back the lens. The Zwo ef adapter is terrible. It has a ton of flexure which will reveal itself at F2.

Also you cannot just let the lens dangle from the bayonet or you will have flexure.

you also need to determine if you have sensor tilt. 
At F2 all of these things are critical.

 

It’s starting to become frustrating to see how much bad advice is so readily offered.

please for the sake of these small businesses that sell camera equipment, do your due diligence before you send something back.

I do have the ZWO EF adapter, but I also have rings supporting the lens at two points, as well as the lens. Would that filter still have any flexure with all 3 points supported?

 

I'll have to figure out how to measure sensor tilt I guess, it seems like from the aberration inspector that the bottom left and all right columns have goofy stars, so maybe sensor tilt is partially the culprit affecting those sides. 

Attached Thumbnails

  • 20220125_174900.jpg

Edited by cdhgamer, 25 January 2022 - 07:01 PM.

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#10 cdhgamer

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Posted 25 January 2022 - 07:14 PM

I did just remember I have an image with a different scope I took with the same camera. The scope isn't perfectly flat across the frame, but it seems more symmetrical than with the Rokinon, so maybe any sensor tilt the camera isn't the main culprit. 

Attached Thumbnails

  • ES102CF.jpg

Edited by cdhgamer, 25 January 2022 - 07:15 PM.

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#11 calypsob

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Posted 25 January 2022 - 08:55 PM

I did just remember I have an image with a different scope I took with the same camera. The scope isn't perfectly flat across the frame, but it seems more symmetrical than with the Rokinon, so maybe any sensor tilt the camera isn't the main culprit.

Immediately I can see you have a spacing problem.
There may be tilt too, try a star test with a .5mm shim.
There are some threads on making a tilt jig for correcting that situation
https://www.bhphotov...ft=BI:514&smp=y


Edited by calypsob, 25 January 2022 - 09:10 PM.


#12 Andy Lucy

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Posted 26 January 2022 - 07:34 AM

My copy of this Samyang lens gave the same sort of image quality as the OP showed in his first image.  I spent a lot of time trying to sort it out, without any success, and eventually sold it (not to an astrophotographer).  My main regret is the amount of clear sky time that I used without getting a single decent image.

 

Is this performance typical?  It’s hard to say, but even in Charles Stark’s original review, where he praised the lens highly, you can see evidence of corner aberrations.  

https://digitalstars...-f2-astrograph/

I have looked at a lot of on-line astro images from this lens and, while some were fine, a number showed problems.  My opinion is that the OP hasn’t necessarily got a lemon - it’s just that this is within the typical performance envelope of the lens.

 

Andy



#13 calypsob

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Posted 26 January 2022 - 10:22 PM

My copy of this Samyang lens gave the same sort of image quality as the OP showed in his first image.  I spent a lot of time trying to sort it out, without any success, and eventually sold it (not to an astrophotographer).  My main regret is the amount of clear sky time that I used without getting a single decent image.

 

Is this performance typical?  It’s hard to say, but even in Charles Stark’s original review, where he praised the lens highly, you can see evidence of corner aberrations.  

https://digitalstars...-f2-astrograph/

I have looked at a lot of on-line astro images from this lens and, while some were fine, a number showed problems.  My opinion is that the OP hasn’t necessarily got a lemon - it’s just that this is within the typical performance envelope of the lens.

 

Andy

I bought 3 of these 135's - 2 Samyangs and 1 Rokinon back to back from E Infinity in 2016 and had no issues. At least not the crazy stuff you see above. You cannot expect TOA 130 quality from any lens especially at F2.  The Samyang has however proven to outperform its Zeiss, Sigma, and Canon equivalents wide open at F2. Look up the tests done by Yuiry Toropin on his flickr page. 

Unfortunately because the price point is easily accessible to beginners on here you see alot of hipshot bad judgment from people who timidly buy this as their entry level lens.  It really is not a beginner piece of equipment.   

This lens is really more of a if you realize what this thing is capable of at F2, then you just smile and run with it because its incredible that this even happened for under $500 its honestly a MIRACLE.  Instead there seems to be this pool of nit pickers who cannot even properly test the lenses before shipping them back to Amazon.  They immediately assume QC issue because someone else said QC issue and it got ping ponged in QC threads 200 times.  So please, learn to check you imaging configuration before sending back the glass and stop disrespecting the legend that is, The Seoul Stardust Slayer. Its an absolute beast in the right hands! 

I can guarantee you Samyang never thought it would generate this much hype, or let alone RGA returns,  it it is highly unlikely they will make another all manual lens of this caliber. If you buy one and truly have a good copy, DONT EVER SELL IT. 


Edited by calypsob, 27 January 2022 - 04:11 PM.

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#14 vidrazor

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Posted 27 January 2022 - 12:22 AM

...it it is highly unlikely they will make another all manual lens of this caliber. If you buy one and truly have a good copy, DONT EVER SELL IT. 

Samyang is now moving into the AF realm with their next 135 and, as Scotty may have put it, a wee bit faster...
 


Edited by vidrazor, 27 January 2022 - 12:23 AM.


#15 calypsob

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Posted 27 January 2022 - 01:24 AM

Samyang is now moving into the AF realm with their next 135 and, as Scotty may have put it, a wee bit faster...
 

Yep no more astrophotography for the 135. Thats all she wrote.

The og lens will become a lost legend


Edited by calypsob, 27 January 2022 - 01:25 AM.


#16 Richie092

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Posted 27 January 2022 - 02:25 AM

Yep. I think that’s a spacing problem. I got cornets like that but if I remember rightly I added .25mm

#17 vidrazor

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Posted 27 January 2022 - 08:37 AM

Yep no more astrophotography for the 135. Thats all she wrote.

The og lens will become a lost legend

Well you never know, it might be a good formula. It will simply need to be tested out.
 



#18 calypsob

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Posted 27 January 2022 - 09:44 AM

Well you never know, it might be a good formula. It will simply need to be tested out.
 

Im sure the image quality will be excellent but if its no longer manual, it will loose its relevance as an astro lens.



#19 FrostByte

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Posted 27 January 2022 - 11:45 AM

I dunno, with a Canon body, you can run autofocus routines with the internal focus motor with APT and Ekos. There might be others, but the ability to refocus periodically with a lens this fast would be pretty great.

Granted, you could always go with a belt and external focus motor, but being able to use the lens’s focus motor would really simplify things.
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#20 calypsob

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Posted 27 January 2022 - 04:15 PM

I dunno, with a Canon body, you can run autofocus routines with the internal focus motor with APT and Ekos. There might be others, but the ability to refocus periodically with a lens this fast would be pretty great.

Granted, you could always go with a belt and external focus motor, but being able to use the lens’s focus motor would really simplify things.

That is true, there is also an astromechanics adapter that runs af via ascom. My concern though is how they design the lens, If it’s for FE only it will be limited to mirrorless, and if it works like a GM lens then you really cannot adjust anything unless there is power going to the lens. That’s what I am concerned with, having everything be manual gives you full control albeit you do you have to introduce your own auto focus system



#21 cdhgamer

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Posted 30 January 2022 - 04:56 AM

Thanks all, I'll look into making sure the spacing doesn't need a tiny adjustment and look into sensor tilt 



#22 erictheastrojunkie

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Posted 30 January 2022 - 10:44 AM

That is true, there is also an astromechanics adapter that runs af via ascom. My concern though is how they design the lens, If it’s for FE only it will be limited to mirrorless, and if it works like a GM lens then you really cannot adjust anything unless there is power going to the lens. That’s what I am concerned with, having everything be manual gives you full control albeit you do you have to introduce your own auto focus system


It will almost certainly be focus by wire requiring electrical control by the camera, thus it will be limited to whatever camera mounts it's available in. Focus by wire sucks, period.
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#23 calypsob

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Posted 31 January 2022 - 04:31 PM

It will almost certainly be focus by wire requiring electrical control by the camera, thus it will be limited to whatever camera mounts it's available in. Focus by wire sucks, period.

I agree. I wish some glass optical wizard would make niche lenses based on infinity focus and fast well corrected fields for astro imaging. Seems like every other niche is filled.



#24 erictheastrojunkie

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Posted 31 January 2022 - 05:55 PM

I agree. I wish some glass optical wizard would make niche lenses based on infinity focus and fast well corrected fields for astro imaging. Seems like every other niche is filled.


Voigtlander's new APO lenses are exactly that, you are limited to Sony E-mount and Leica M-mount though, and any camera like the Nikon Z's that you can adapt to. I've also had a forum member 3D print adapter so I can use them on my ZWO cameras with some great success.

#25 calypsob

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Posted 31 January 2022 - 08:09 PM

Voigtlander's new APO lenses are exactly that, you are limited to Sony E-mount and Leica M-mount though, and any camera like the Nikon Z's that you can adapt to. I've also had a forum member 3D print adapter so I can use them on my ZWO cameras with some great success.

I wonder what it would cost to have 25 of those adapters machined in 6061


Edited by calypsob, 31 January 2022 - 08:09 PM.



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