I'm sure I'm not the only one with this problem, but I can't seem to get the stars in focus given the focus travel of the prime lens.
Anyone have a better fix than Nico Carver's 'lens surgery'? I will try that as a last resort!
Thanks for any help!
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what camera and filter are you using? |
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What are you shooting with?
I use that lens with either my Canon M50 or Canon RP. Have never tried it with a dedicated OSC. I do know for the two DSLRs the focus point is just a hair back from the focus stop at infinity.
Canon M50 with its M-EF adapter has a back-focus of approx 48mm.
RP with its R-EF adapter has a back-focus of approximately 44mm.
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I use the 533's and 2600's and a 1600 ASI with the ZWO canon EF lens adapter with Filter drawer. I use an EAF for focusing via SGP. https://www.astrobin.com/o2woko/I can provide the EAF settings for SGP after work. But I have them in one of my early Samyang images if you cant wait... i hope you figure it out. I really enjoy this Rig as I hope you will! CS Tim
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I'm sure I'm not the only one with this problem, but I can't seem to get the stars in focus given the focus travel of the prime lens. Unless something is wrong with your copy of the lens, focus for stars in my Rokinon 135 with an Astro camera and a lens filter drawer is a 1/4" back from the focus stop. I use a Bat mask to get mine in focus and it stays there. I do not use an EAF with mine, have not needed to once it's in focus.
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I also had a very time getting good focus with my Samyang 135 (same as Rokinon). The focus ring is just too sensitive, I cannot find the perfect spot manually, even with a bahtinov mask. I installed the Astrodymium ring system and a ZWO EAF. I considered this an investment because it is a great lens for astro and I wanted to be able to use its potential as much as I can.
You don't even need a PC to control the EAF. If you are still doing things manually you can get the optional hand controller which will give you much more precision than manually turning the focus ring.
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Both of my copies have been able to focus at infinity from the get go, but I still did the mod to have some more space for the EAF to work. I suggest you do the mod. It's very straight forward and you can't do anything wrong as long as you follow the steps.
You can easily test this by shooting at something in the distance, I use mountains. You'll quickly notice if the image comes into focus or not with a regular camera. As long as you can't reach true infinity, the mod is the only solution.
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Mine has no problem whatsoever focusing, without any mod to the lens. Regarding the focusing, it's surprisingly simple : either it focuses or it does not. On mine it does so perfectly, as with any other camera I own. Mine once it's in focused it stays there for months if not years, no need for extra gadgets. My sensor is 17.5mm behind the camera front 42mm threaded flange. I use a camera adapter (I think it's 42mm to Canon EF mount) with filter drawer, I believe it was from Agena. I am guessing the brand is Zwo. Some images here : https://www.astrobin.com/search/?q=Rokinon+135mm+Hamber |
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Just to clarify; The mod itself is a simple procedure of removing three tiny screws and a hard stop mechanism. The lens will still have a hard stop as the grooves on the helicoid aren't infinitely long, but it should now focus a bit further than infinity which allows for sharper and better focusing at distant objects like stars or even landscape. It also simplifies the AF routine with an EAF as you don't necessarily have to change too many settings (like reverse movement etc). Which is why I have decided to mod both of mine, just to squeeze any bit of left over potential from them. The mod will not in any way damage the lens, and it is reversable at any time. Once you pull the rubber grip back on, it's like nothing ever happened externally  |
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I'm sure I'm not the only one with this problem, but I can't seem to get the stars in focus given the focus travel of the prime lens.
Anyone have a better fix than Nico Carver's 'lens surgery'? I will try that as a last resort!
Thanks for any help! More information is really needed. What camera are you attaching to? Is it spaced properly for that camera? Etc.
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If your backspacing is too far off you might not be able to reach focus. It might be too short.
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NovaAstrophotos:
what camera and filter are you using? *** Sorry, was at work! I am just using an astro modified Nikon D5300 so there should be no problem with backfocus, there is a UV/IR cut filter on the front of the lens ***
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I just posted this picture that I took last night as you can see I can clean it up at lot with BlurXTerminator....maybe the lens was too warm when I was trying to focus early in the night... https://www.astrobin.com/sj6t53/ |
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I just posted this picture that I took last night as you can see I can clean it up at lot with BlurXTerminator....maybe the lens was too warm when I was trying to focus early in the night...
https://www.astrobin.com/sj6t53/ It won't win awards but the focus is not that bad but you don't say how you focused so it's hard to respond. It looks like a back focus issue, stars are just wonky in the corners, hard to tell you how to fix since you don't tell us what your setup even is.
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That is one nice picture !!
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