Samyang/Rokinon 135 - to EAF or not to EAF. - Forums

Topic starter

Feb 2, 2022 · Edited: Feb 2, 2022

Hello, just a quick one to get some info of someone with experience on the Samyang / Rokinon 135mm.
Just ordered this lens and hoping to turn it into a third little wide field rig for imaging.
(Playing around at F2 should be fun compared to the F5's of my other rigs)

I'm now working on figuring out the best mounting solutions, which comes with the question:
how well does it maintains focus during the night? And how often do you adjust it?

as I'm seeing conflicting stories depending on where you're looking, which is understandable at F2. And I'm trying to figure out if I should be buying mounting solutions that are able to hold a ZWO EAF... or; if I can save a bit of money and just go for a standard mounting solution + bahtinov mask.

And I'd rather not waste money on the more expensive mount + another ZWO EAF it if it isn't needed.
Or find out later I should have spent the money because it was needed and need to buy an entire different mounting solution.

Thanks!

Dan Kearl

Feb 2, 2022 · Edited: Feb 2, 2022

Mine holds focus… they are so wide you hardly have to polar align.
Stars are so small that Bahtinov mask is not really necessary either to get them in focus.
I use mine in the most simple star tracker mode with just ball head and camera and it works fine.

kuechlew

Feb 2, 2022

Dan Kearl:
Mine holds focus... they are so wide you hardly have to polar align.
Stars are so small that Bahtinov mask is not really necessary either to get them in focus.
I use mine in the most simple star tracker mode with just ball head and camera and it works fine.

I don't own the Samyang 135mm (yet) - too much Canon glass lying around - but based on my own experience in this focal range I can only agree with Dan's statement. However, you don't mention what camera you intend to use. In case you're going to use the ASI 183 - as in your published images - it will turn into an effective focal length of almost 400mm and things may look quite differently.

In your case I would try out Dan's recommendation to come up with an own conclusion. If you then need more precision you may still go for the EAF.

CS
Wolfgang

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Steven

Topic starter

Feb 2, 2022

Dan Kearl:
Mine holds focus... they are so wide you hardly have to polar align.
Stars are so small that Bahtinov mask is not really necessary either to get them in focus.
I use mine in the most simple star tracker mode with just ball head and camera and it works fine.

I don't own the Samyang 135mm (yet) - too much Canon glass lying around - but based on my own experience in this focal range I can only agree with Dan's statement. However, you don't mention what camera you intend to use. In case you're going to use the ASI 183 - as in your published images - it will turn into an effective focal length of almost 400mm and things may look quite differently.

In your case I would try out Dan's recommendation to come up with an own conclusion. If you then need more precision you may still go for the EAF.

CS
Wolfgang

Thanks for the reply Dan and Wolfgang,

I'm not quite sure yet what camera I will be using for it. For now it will probably be the 183MM or 183MC, I'm aware these aren't great fits for the focal length with the small sensor. I do have a (home) modified Canon 1200d laying around too, I might use that to make better use of the focal length and to see how it performs.

Thanks very much for the feedback!

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andrea tasselli

Frequent contributor

Feb 2, 2022

I don't have the samyang (I wish I have) sadly but to give a bit of prospective; with my nikkor 300mm AFS @ f/2.8 I have to refocus about every 2 hours if the temperature drops more 3 degrees.

Concise

Chris Bailey

Feb 4, 2022

I ran an SY135 for a whole season with an Ha filter and it is a lot of fun. I stopped mine down with step rings to about f2.6 to get better peripheral star shapes.

I added autofocus to mine using a highly geared stepper and timing belt and used the myFocuser control and as such a single step was all but perceptible. It consistently got far better focus than I could ever do manually.

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Morian

Feb 4, 2022

I have Samyang 135 F2.0
It's a great optics but you write "could be exciting to play around f2 but in my experience it is almost impossible to work in as there is so much and not least short FL that exposure time will be so short but you are welcome to try .
I do not want to take the excitement from this but as it is it is impossible and I can max work in F2.8 or it will be overexposed.

hha

Feb 4, 2022

I have the Oshiro 135mm f/2.8. The image quality at f/2.8 in the APC format is OK, improving to very good at f/4 in the APC format, no CA. in FF several pixels of coma are visible. Focusing at f/2.8 is so critical, that I am using it at f/4 only. Even there, a 0.5mm shift on the focus ring is seen as a shift from red to cyan rings about bright stars. In 4 hour runs (240x1min subs) the focus is stable.

hha

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Brian Boyle

Feb 4, 2022

Hi Steven,

What a great question, and very timely from my perspective as I contemplating the same question for my Nikon 200mm f2 lens.

I am moving towards an autofocus solution for my camera lens, largely influenced by @Michael Feigenbaum (whose work I very much admire) who has recently set up his Samyang 135mm with an Astrodynium ring + ASIAir automated focus system. Indeed the more I looked, the more purpose-built automated focus solutions I found for the Samyang 135mm lens (DeepSkyDad).

This existence of this market - specifically for the Samyang 135mm lens - suggests there is a need. Or at least a perceived one.

My own experience with first my Canon 200mm f2.8 (operated at f4) and now my Nikon 200mm (operated around f2.5, courtesy of a milk carton wedge) is that the need is very much driven by lens quality, f-ratio and temperature change. No surprises there. My Canon lens rarely needed refocussing during the night, unless the temperature changed by over 5C. In contrast, I notice significant de-focussing with the Nikon after 2degrees temp change. Currently we are going from 30C days to single digit dawns, so temp change is a big issue here.

Getting the focus point accuruate to begin with is also important (no s**t, Sherlock) and previously a Bahtinov mask was "good enough" to give me sub-2pix on the Canon. But again the Nikon is much more challenging to focus accurately this way, and is really at the limit of my dexterity.

For these reasons, I have also chosen to go with an automated solution, and have ordered another ZWO EAF, a bracket from TS and a 3D printer cable and pulley to lash the focusser to the focus ring on the Nikon. We will see how well this works. All up this cost around USD300, which is a small extra on top of a system which I hope will give me many hours of (unattended) pleasure.

CS Brian

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Peter Oberč

Feb 4, 2022

I'm not quite sure yet what camera I will be using for it. For now it will probably be the 183MM or 183MC, I'm aware these aren't great fits for the focal length with the small sensor. I do have a (home) modified Canon 1200d laying around too, I might use that to make better use of the focal length and to see how it performs.

Now that's classic photographer's point of view

IMHO, IMX183 is the best sensor for fast lens, as the fast f-ratio (at least f/2.8) overcomes the issue with small pixels having small surface area and not gathering enough light (I know, I'm dying with this sensor at f/4 with 20h exposures...) but you still get the MAX RESOLUTION benefit with these small pixels. 135mm + 2.4 microns gives 3,67"/px. which is decent for super-wide-field. The real question is will you be able to get nice field and stars at f/2 or will it have to be stepped down to f/2.8...

Anyway, in my mid-term plans there is a uper widefield setup - comprising of either Samyang 135 or Sigma Art 105 + QHY183C. And in this plan - for focusing - I would go with DeepSkyDad solution specifically for the Samyang, seems like a proven no-fuss solution.

Peter

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Michael Feigenbaum

Feb 5, 2022

Thank you @Brian Boyle ! I am a big admirer of your work too…. I would highly recommend some kind of mounting apparatus like the Astrodymium simply because you can use an EAF with it. My experience in Arizona where there can be 10°C or more temperature change through a night is that the Samy did not hold focus all that well. The EAF works wonderfully with the lens and the hardware for using it which comes with these Astrodymium type devices.

When I bought the lens I had exactly the same thing in mind, a nice very wide field setup for traveling or home use. But I really did not want to be refocusing every hour so I put it on the shelf. Then I happened upon this solution and I could not be happier. It is a fantastic lens and with that nice 67mm aperture at f/2 quite a little light bucket.

I use mine with the small pixel ASI183mm with an electronic filter wheel and it is very nice. I do intend to use the ASI294mm in unlocked bin mode (2.315um pixels) for my next images because of the bigger 4/3 sensor.

Hope this helps!

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Steven

Topic starter

Feb 5, 2022 · Edited: Feb 5, 2022

Thanks for all the comments. It's helpful and appreciated.
It would appear that an EAF option would be the best way to go!

Peter Oberč:
Now that's classic photographer's point of view

Yes, it is more a photographer's point of view. As my focus with this rig is wide field and FOV.

I understand that 135mm and the 183 is one heck of a combo. Like yourself, I know that the 183 is a great sensor, but that it can be an absolute nightmare to get enough light into those tiny tiny tiny pixels. And it's a bit frustrating to sometimes see what others are posting with 2-3 hours worth of exposure, and here I am working away to get 20-30 hours into a project.

The Samyang could might that a bit, the F2 (or 2.8 ) could perhaps light than my F5 and F4.9 refractors. So for a single image, that might work great.
But I do hope to (sometimes) use this as a mosaic setup.. but with the 183 sensor, I'm already having to do 2-4 panels just to fill in the same size that I could be doing with 1 APS-C sensor + due to the small pixels, I would also probably need longer exposure times to do this with the 183.

A nice 8 panel mosaic, of 1hr each panel with a "larger pixel" APS-C sensor might mean 24-32 panels at 1.5-2 hours each with the 183 to cover that same part of the sky. - Which might defeat the purpose and "idea" behind the rig.
Yes the resolution would be incredible! But I'm just not sure wether or not that is a trade-off I'm willing to make (yet).

Obviously, once I have the rig running I'll have a better idea of what kind of results I can expect and what the rig can be used for.

Michael Feigenbaum:
would highly recommend some kind of mounting apparatus like the Astrodymium simply because you can use an EAF with it.

That looks like a great solution! Just sad that it doesn't appear to be easy to get in Europe. Delivery times said to take more than a month.
I did find a similar setup from "Wega", but that one does offer less mounting solutions for an additional rail or the asiair mount. So, still undecided on that.

andrea tasselli

Frequent contributor

Feb 5, 2022

The Samyang @ f/2.8 is just 48mm of aperture. It would be no better than a Redcat 51 and in fact I expect it to be worse by a margin in terms of light collecting abilities.

Hugh Coleman

Mar 25, 2023 · Edited: Mar 25, 2023

I managed to find a mint example second hand soon after borrowing one from the club member earlier in the year.
It seems my example is a touch better optically than the one I borrowed, as after my trials I was not convinced, but pushed the button on mine anyway because the deal was pretty good.
I have done three sessions of the Vela SNR with it and been very happy with the results. the first two sessions were testing the ZWO 533 MC Pro against the ZWO 294 MC Pro. I came down on the side of the 294 (My wifes - I then swapped my 533 with her for the 294) on account of the wider FOV. Otherwise, they are similar resolutiion.
The third session was a four panel mosaic of the same region (Vela) to get an even wider view.

Points to note.
- I focussed at F2 and actually ran my first two trials at F2 (in error), but it was fine sharpness wise and flat corner to corner. No CA was obvious.
- For the four panel mosaic, I stopped down to F4.0. No noticeable change in star shape or sharpness.
- The lens came with a Hoya UV (C) Cut filter. I left this on. However, there was a noticeable Halo around particular stars, not the brightest or the hottest, I think they were a particular spectral class maybe. So there are four or five large white halos to be seen in ALL my trials. So F Stop makes no difference here.
- Focus as set at the beginning of the sessions was maintained throughout without the need for an EAF.

I'm in the process of fabricating a ring and rail setup for the lens. I think it will make life easier later changing from other refractors to this in any mount. And it looks pretty cool.

Anyone interested in seeing the images, please message me.

Cheers,

Hugh

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Frank "Voloire"

Mar 25, 2023

No way to get decent focus without EAF, some examples with different sensor and f/stop and fiters:

F2.4/APS-C https://www.astrobin.com/g9jgyd/D/
F2.0/ZWO 533 https://www.astrobin.com/g9jgyd/D/
https://www.astrobin.com/4y9la8/?nc=&nce=
https://www.astrobin.com/h9q0cw/B/?nc=&nce=

Hope it helps

CS

James Ross

Mar 25, 2023

I bought a second hand Samyang 135 about a year or two ago and I managed without an EAF for the first year but I eventually noticed my narrowband filters were needing small focus offsets relative to each other when using this lens which was a pain to deal with manually. Never had any trouble with temperature shifts. In the end I just bought a second hand ZWO EAF and 3D printed one of the setups available on Thingiverse. I have a deep-sky dad AF for my other scope and can recommend them too. In astrophotography terms adding the EAF setup wasn't too expensive, I wish I had done so at the beginning just for the convenience.

Agree with the others that recommend stopping it down to 2.8 or slower as otherwise the off axis aberrations can get quite severe. If they're a problem you can avoid diffraction spikes by using a circular screw-in stepdown ring - very cheap off ebay.

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KennethK

Mar 25, 2023

I love the Samyang 135mm. When stopped down to 2.8 its supersharp. I highly recommend the EAF with this lens. The focus shifts a lot during the night, at least in mine conditions, so the EAF is a must for me. This was my setup until I recently bought the Astrodymium system.

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GalacticRAVE

Apr 9, 2023

to those using an EAF with the Samyang 135: how do you deal with the hardstop at infinity? while mine focuses a bit "short" of infinity for stars, there is not much room right of focus to get a V curve.

Matthias

Frank "Voloire"

Apr 9, 2023

to those using an EAF with the Samyang 135: how do you deal with the hardstop at infinity? while mine focuses a bit "short" of infinity for stars, there is not much room right of focus to get a V curve.

Matthias

Let's try to use the "reverse" setting in your favorite acquisition software for the AF routine

CS

GalacticRAVE

Apr 9, 2023 · Edited: Apr 9, 2023

Franco - thanks, but I am not sure how this is going to help? sure I can start from the stopper and go short, pass a minimum - so far so good. but the autofocus routine usually are configured to go the same factor HFR/HFR_min (say 3) on either side of the minimum - so after finishing left of the curve it will try to add points on the right wing of the V and run into the stopper. Or am I missing something?

Michael Feigenbaum

Apr 10, 2023 · Edited: Apr 10, 2023

I had the same focus issue with the lens using a filter wheel. Ended up that I had to remove the stop block in the lens to get it to focus at infinity. It was a simple procedure and can easily be reversed. @Nico Carver has an excellent video showing exactly how to do this on his YouTube channel.

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GalacticRAVE

Apr 10, 2023

Thanks Michael! I was hoping to avoid it, but if it has to be - it has to be.

Matthias

psychwolf

Apr 10, 2023

For anyone using the autofocus, what are your step size settings and other details for ensuring the autofocus both can get enough to create a V curve, and then can adjust the focus not too much?

I've got a ZWO EAF hooked up to the Rokinon using ASIAir, but keep having difficulty in that the EAF doesn't nail the focus and goes too far. So usually I have to manually adjust it to just nearly infinity focus half the time which defeats the purpose of EAF!

Phil Creed

Apr 10, 2023

Mono might be a different story, but I've never felt the need for an EAF using OSC.

Even at old-school-Megadeth levels of screaming fast, it's still 135mm focal length. Roughly 6"/pixel for many cameras. I just focus with a Bahtinov mask and call it good. By the time the delta T might warrant changing focus, I've already collected enough light at such fast f-ratios to call it a night, anyway.

Clear Skies,
Phil

Dan H. M.

Perfect post

Apr 10, 2023

Phil Creed:
Mono might be a different story, but I've never felt the need for an EAF using OSC.

Even at old-school-Megadeth levels of screaming fast, it's still 135mm focal length. Roughly 6"/pixel for many cameras. I just focus with a Bahtinov mask and call it good. By the time the delta T might warrant changing focus, I've already collected enough light at such fast f-ratios to call it a night, anyway.

Clear Skies,
Phil

Same here. I’ve had the lens imaging all night a few times now and never had to refocus. The 3D-printed kits that let you attach the EAF are neat but I generally prefer to secure the lens with a sturdy tripod collar.

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