Imaging with the Samyang 135mm f2

[Elp]

Pretty stunning @emyliano2000. I also agree, no need to stop imaging unless you're too far north/south or other circumstances don't allow. I recently did my first mosaic, a nine panel wide galaxy one in the imaging section, it just encourages you to keep expanding it.

[ollypenrice]

Regarding Samyang star shapes, my team of  three finds them reasonable, but not perfect, on the 2600 chip at F2. But here's the thing: how good do they need to be? This is a very widefield optic, obviously, and, being small, will produce large stellar images. However, we now have StarXterminator or Starnet++ and we have the option of reducing the stars to a scale commensurate with the wide field - meaning very tiny. How good do tiny stars need to be? Any significantly-sized stars can be fixed by a one-click action and most will be too small to matter.  I have no intention of beating myself (or the lens) up for shortcomings which will, in the finished image, be trivial. My motto is, 'Look at the big picture.'

Olly

[Adreneline]

19 hours ago, emyliano2000 said:

I hope you like it.

I do like it! Personally I prefer the colours to be less vibrant but that said the structure and detail is very revealing - especially this bit:

Never mind "the fingers of God" ..... spooky!

Adrian

[900SL]

Has anybody used a Blackcat EAF set up with the SY 135? 

I have my SY 135 on a Redcat 51 ring and handle, so if I could McGiver a Blackcat to work that would be dandy

[Space Oddities]

Hi Richard,

I do! Overall it can be used on the Samyang, but not the the geared ring. The one that comes with the black cat mount doesn't fit properly the Samyang. The diameter of the lens differs from that of the RedCat, although very close.

To overcome this, the creator of the Black Cat Mount sent me another ring with a different diameter. It worked fine! However that was more a prototype/test. Also, I am not using it anymore because I ran into some problems.

I'm actually not a huge fan of this gear mechanism, and I am in the process of switching to a pulley/belt system. I 3D printed this adapter for the Samyang, and will use a GT2 pulley and timing belt on the Samyang. Hopefully this will solve the problem I had (focuser getting stuck).

I would advise you to do the same, and find a GT2 pulley and belt of the right size. I think it's much better! 

For the adapter, I ordered a print and it cost me about 15€. The Pulley and belt are a few € more, so overall, quite a cheap DIY if you already own the Black Cat mount!

Hope that helps  

Edited July 5, 2023 by Space Oddities

[Elp]

Focus pulling (what this is effectively doing) was designed into the video version of the lens which has external gear teeth built into it. Just another option for those who don't have one yet. I would like to note, the usual infinity adjustment I don't think is possible on the video version of the lens as it's built different.

Edited July 5, 2023 by Elp

[Albir phil]

Hi it is possible to gain some extra focusing distance by removing the focusing stop located behind the rubber focus grip 👍

[Len1257]

On 01/07/2023 at 12:22, Space Oddities said:

I found the link on Astrobin, but can't remember where. I saved the STL file though, maybe that will help!

I printed it in PLA Pro, 80% fill, 0.1mm resolution. I don't know anything about 3D printing but that seemed fine!

6485c7fcc370e_9cb257b709c87bd2122436b5c6f0058c.stl 2.82 MB · 7 downloads

The STL is all I needed but not difficult to find on Thingyverse. Thanks Len.

[900SL]

19 hours ago, Space Oddities said:

Hi Richard,

I do! Overall it can be used on the Samyang, but not the the geared ring. The one that comes with the black cat mount doesn't fit properly the Samyang. The diameter of the lens differs from that of the RedCat, although very close.

To overcome this, the creator of the Black Cat Mount sent me another ring with a different diameter. It worked fine! However that was more a prototype/test. Also, I am not using it anymore because I ran into some problems.

I'm actually not a huge fan of this gear mechanism, and I am in the process of switching to a pulley/belt system. I 3D printed this adapter for the Samyang, and will use a GT2 pulley and timing belt on the Samyang. Hopefully this will solve the problem I had (focuser getting stuck).

I would advise you to do the same, and find a GT2 pulley and belt of the right size. I think it's much better! 

For the adapter, I ordered a print and it cost me about 15€. The Pulley and belt are a few € more, so overall, quite a cheap DIY if you already own the Black Cat mount!

Hope that helps  

Thanks Mr P. PM sent.

[900SL]

On focus, I found that adding a filter to my ZWO adapter pushed the focus out beyond the range if adjustment. 

Easily resolved by adding a 1mm shim to bring it back. Next dark evening I'll check the corners for accurate backspacing

[Petrol]

I decided to go EAF with the Samyang now I've got the back focus sorted. My options seemed limited but I went for the Thinkable Creations Hyperpod.
I appreciate that 3D printed parts are not the most rigid so a bit of beefing up was in order. I made some pre preg carbon fibre plates to replace the 3d printed ones and fitted some further re enforcing.

 

 

The dovetail was replaced with an alloy one and since the camera is a bit heavy, I fitted a WO guidescope ring to support it.

 

 

It's all looking good. The next problem is to set up the ZWO EAF which I've never done before.
If anyone is using NINA and would be kind enough to share their autofocus step size / backlash settings I'd be very grateful as it would be a great starting point. I know backlash varies between belt drive and meshed gear systems but I'm starting from zero ☺️

Clear skies and roll on the dark skies!
Pete

[aleixandrus]

Wow, it looks amazing but, to be fair, a bit overkill IMO given the pixel scale. I use the Astrodymium kit and it just works out of the box. However, I'm thinking adding support to the camara (ASI183MM) because despite having the Canon bayonet replaced with the M54 (M48?) adapter, I think I'm having some tilt...

Regarding EAF, I use NINA with 50 step size (I think I can lower this) and 150 backslash using the overshoot method. I also set 4 steps displacement from initial focus position (I try to set the initial focus manually good enough for plate solving). I'm talking from memory but I can share some screenshots if you need more details.

[Petrol]

On 16/07/2023 at 20:36, aleixandrus said:

Wow, it looks amazing but, to be fair, a bit overkill IMO given the pixel scale. I use the Astrodymium kit and it just works out of the box. However, I'm thinking adding support to the camara (ASI183MM) because despite having the Canon bayonet replaced with the M54 (M48?) adapter, I think I'm having some tilt...

Regarding EAF, I use NINA with 50 step size (I think I can lower this) and 150 backslash using the overshoot method. I also set 4 steps displacement from initial focus position (I try to set the initial focus manually good enough for plate solving). I'm talking from memory but I can share some screenshots if you need more details.

I agree, it's a bit OTT. The plan was to stiffen it up a bit but I kept going.
Thanks for the NINA AF settings, saved me a lot of hassle!

Clear skies
Pete

[aleixandrus]

I've checked my settings and I confirm my previous values (50 step size, 150 overshoot, 4 displacement steps). However, I experiment with different step sizes (25-50-75) as I read that the recommended difference between minimum and maximum HFR values should differ x3-4 times for a good and consistent AF. Your graph (and mine!) shows ~5 / ~11 HFR, this is, x2 difference. This also happens to me and I can't make this different bigger without messing *a lot* that step size. However, AF seems to work well enough so I finally set 75 as default step size when stopping down the lens at f/2.8 using the ZWO EAF (12V version). I suppose working at this fast focal rations things may be different compared to more conventional scopes, I don't know but hope this helps.

PD: That 'V' shape seems right but I think you still have a 'bug' in your AF procedure, @Petrol 😂

[aleixandrus]

Well, I had some issues recently with my Samyang, my Baader SHO filters, backfocus, guiding… I think I sorted out most of them (or at least minimize them to my standards) to the point it worth to explain them a little so I can help others with my achievements. Let’s go!

My current OTA is:

• Samyang 135mm stopped down to f/2.8
• Astro Essentials Samyang Lens to M48 Adapter
• ZWO 16.50mm M48>M42 adapter (the one provide with the camera)
• ZWO EFWmini 5 position filter wheel
• ZWO ASI183MM Pro

These elements add, respectively, 0+16.50+20+6.5 = 43mm. I need 44mm total backfocus as I’m using the Canon EF lens version. I also use the SHO Narrowband CMOS optimized Baader 6.5nm filters, 2mm thick. It is well known you should add 1/3 to backfocus, this is, 0.67mm. So, in total, I need to add 1.67mm using spacers.

I bough the ‘Artesky Fine Tuning Ring Set T2”, a cheapo kit of 10 metal spacers from 0.1-2.0mm. Spoiler: bad purchase; they are not labelled and use poor quality inspection techniques, their thickness is not consistent and some are very slightly bended but enough to introduce tilt (to my eyes). However, I add 1.0+0.5+0.15=1.65mm spacers and made some tests.

I don’t want to bore you with all my troubles but, although my Ha shoots seemed just ‘right – but not good’, when I purchased S2/O3 filters and tried to mix all channels, that was a mess. Just one representative sample:

As a whole, I like the image (this version is edited to taste but not carefully) but those corners are just awful even with some star reduction. This is going to get me into troubles in the future for sure (mosaics or when adding RGB stars, for instance) so I need to address them. This is all close I could get to the supposed ‘right’ backfocus after many nights of AF tuning parameters, manual focusing, mess up with 0.1mm rings, etc. At that fast ratios, a 0.1mm spacer makes a BIG difference but I tried to set the infinity mark ‘just in the base of the L mark of the lens barrel’, as many suggest. None worked. Discarding the user error or AF misconfiguration, I opted for a more drastic approach: forget about the ‘right’ backfocus and adjust the Samyang mechanically.

My first step was reinstall the Astro Essentials M48 Adapter and make sure it was not overtightened and check for evident tilt.

 

First lesson: the Astro Essentials M48 Adapter has the same size, height and thickness than the Canon mount so any measurement regarding backfocus can me done from the face of the adapter, just as you should do with the original mount. This is a common question in this forum.

My second step was to check if the infinity position of the Samyang was accurate, at least to take it as a reference point. Spoiler: it was not. This video from Nico Carver (Nebula Fotos) is very helpful so I don’t will repeat this info. The procedure is quite simple, it takes 10 minutes and has no troubles, anything can be undone, but I take these variations:

1.       Instead removing the infinity hard stop, to have room when past the correct infinity focus to avoid damaging the motor of the EAF, I just move one position using the same screws. This way I still keep a hard stop to prevent (possible, don’t know for sure) damaging the lens if I go waaaay out towards infinity and all lens parts keep stored inside

2.       I checked that the external lens barrel, the one with the ‘L’ mark, is just placed with three screws *with no precision at all*. That mark is essentially useless if the lens was not assembly with care. If your stars are not right, you just cannot trust it.

Left: before / Right: after. Pay attention to how I’ve displaced the infinity stop just one screw position, so it still works. The bottom row shows how hard stop position shifts, leaving enough room to past infinity during the AF procedure but still maintaining that hard stop.

Detail of the focus ring fastening. There are 3 screws like this which hold the whole focus sing. Pay attention to the amount of adjustment space available, which directly impacts on the precision of the ‘L’ mark position (the whole focus ring piece is market in blue). Those screws may loosen up for many reasons (temperature shift along the years, excessive stress over the focus ring, lens aging, poor quality assembly…) so you can’t really trust that mark. I suppose that’s the reason why many in this thread disagree on where to set infinity respect the ‘L’ mark.

The ’correct’ procedure should set infinity focus based purely on a test image and then disassembly the lens and move the focus barrel according to that, so the ‘L’ mark is in the correct position, ie., calibrate the focus barrel. I think this effort is not worth it. But, if you feel you are too close to the infinity stop, displace it a bit to have more room, it is an easy task with minimal risk and reversible.

I have a 77-49mm step down ring to step down the lens to ~f/2.9 (I’m not sure this value is correct, I need to check it) instead using the aperture ring (so I can avoid spikes in brighter stars). I suspect this element may deform the stars in the corners or introduce tilt, somehow, so the next attempts were done stopping down the lens to f/2.8. I prefer to ensure backfocus first and try this later.

Finally, I made some tests with different spacers, again. However, this time I did some DIY to the metal spacers to ensure flatness using a sandpaper, rasp. As I said before, bad purchase but it was all I have for now. I use NINA for autofocusing using both internal NINA algorithms and Hocus Focus plugin. The later uses multiple measurements in all corners and centre so you can find more accurately how your optical train behaves, including backfocus issues and tilt. You can also re-run the focusing process offline (during the day) with different parameters, so it is very helpful to address issues. HOWEVER, I could not get consistent results between their indications and my visual inspection. I don’t know why, it may be user erro or wrong plugin configuration. After some test, disassembling the whole setup each time, I added the only 2mm spacer ring, adding a total backfocus of 45mm, which is not 'the correct' backfocus. Is this right? I don't know and I don't care: although not perfect, it is way better than my previous attempts and purely based on visual inspection,  it is good to me (at least for now).

7.5h total exposure (2.5h per channel). Data stacked and calibrated with darks/flats/darkflats and WBPP in PixInsight. No noise reduction nor blurxterminator-like apps, just Automatic Background Extraction, RGB channel combination and curve adjustment to taste.

 

 

This one below is the original full resolution picture (if the attachment worked fine 😅) if anyone is interested in viewing more details. To me, bottom right corner shows some tilt (it is more visible in the subs) BUT given the effort that take me to reach this point, I’ll try imaging for a while and have some fun. I will evaluate the 77>49mm ring in the future and, maybe, a rotator/tilter, but the later will be too problematic given the large the FOV, the difficulties doing flats and the possible tilt at this fast f-ratios, so I'll probably pass.

This Samyang mega-thread was VERY helpful so I expect this may help some of you who are having troubles with this lens and give something back to the community, not everything should be ask for advice. Feel free to ask/correct anything!

Edited July 20, 2023 by aleixandrus
Added YouTube link to NebulaPhotos channel I've forgotten

[aleixandrus]

Let me add this picture to complement my previous post. Top row shows the stacked SHO channels, bottom row shows the single SHO subs. I think it clearly shows I still have room to improve, specially in the O3 filter and that right side (tilt?). However, the final edited version seems just right. IMHO, starts in SHO color are not great so I'll probably use the ones in the Ha sub despite being white. I'll deal with stars shapes in the future when I buy RGB filters and a bigger filter wheel. For now, as I say before, I think this is 'well enough' and I think I deserve some fun just imaging without dealing with technicalities. But feel free to contradict me 

PS: those subs are just random selected subs for illustration purposes, some AF issues may happened there, specially in the O3 channel!

Edited July 21, 2023 by aleixandrus

[Adreneline]

2 hours ago, aleixandrus said:

For now, as I say before, I think this is 'well enough' and I think I deserve some fun just imaging without dealing with technicalities.

Sounds like a good plan!

You have been very thorough in your investigations and preparation. In my case I base the focus position for my lens purely on the result from using the Canon 6D, which when focused at infinity (or for sharp stars and perfect BM pattern) is right in the middle of the base of the 'L' - what is good for the 6D will be good for my ASI camera - or that was my thinking.

I have now switched my ASI183MM for my ASI1600MM - (I still get one dodgy corner so it is not the sensor!) - and I am going to try using my ASI183MM with my f1.4 Samyang 85mm manual lens. As it turns out the f.o.v. for the SY1600 combination is almost identical to the SY85 combination - what luck! I've ordered the M48 adapter so once that arrives I shall have all sorts of fun trying to establish the correct spacing all over again - joy!

Clear skies and thanks for the interesting write-up - and photos!

Adrian

[Elp]

Have you tested the 85mm? I've had a variety of Samyangs and the 135mm is a very rare exception, if you look at it's MTF graphs it is nearly just as sharp to the corners at full frame at f2 compared to f8. Most lenses I've found are not anything like this, even Samyangs own. Generally if it doesn't have ED lenses in its construction I've found they fail at star imaging. My last one was a 50mm f1.4 aspherical (non ED), though it was fast it was only usable maybe 50pc of the FOV as it suffered very bad CA and LoCA. The venerable 14mm is an ED type and one of the best for very wide field.

Edited July 21, 2023 by Elp

[Adreneline]

2 hours ago, Elp said:

Have you tested the 85mm?

No, not yet. Have you?

Edited July 21, 2023 by Adreneline

[Elp]

No. I know the 85mm f1.4 FE version is supposed to be a good lens so if yours is similar it might be great, just thought I'd mention it before you spend a lot trying to adapt it. Worth taking a few manual shots on a fixed tripod to try out first.

[ovrcome]

ZWO EAF Autofocus HELP!!! Using ASIAIR Pro. I have searched this topic for weeks and even performed the mod Nico Carver suggested on the Rokinon 135mm and no matter what I do, when I try to use autofocus, the automatic out and in focusing hits infinity and causes my gear to skip and I simply cannot autofocus. I have attached my setup design. Any help from the community would be greatly appreciated! 

Edited July 21, 2023 by ovrcome

[Adreneline]

1 hour ago, ovrcome said:

when I try to use autofocus, the automatic out and in focusing hits infinity and causes my gear to skip and I simply cannot autofocus.

Sorry to hear you are having problems. Frustrating!

Have you tried setting the Reverse option?

I measured the Backlash on my system accurately and chose my Fine and Coarse based on the backlash figure; as I understand it the Backlash is not used in the Autofocus routine. As you have a different gearing arrangement I assume you need to use different Fine and Coarse figures.

Fingers crossed this helps.

 

[ovrcome]

13 minutes ago, Adreneline said:

Sorry to hear you are having problems. Frustrating!

Have you tried setting the Reverse option?

I measured the Backlash on my system accurately and chose my Fine and Coarse based on the backlash figure; as I understand it the Backlash is not used in the Autofocus routine. As you have a different gearing arrangement I assume you need to use different Fine and Coarse figures.

Fingers crossed this helps.

 

Thank you!! I will try these settings tonight! 

[Adreneline]

42 minutes ago, ovrcome said:

I will try these settings tonight! 

It can be tempting to use a large Coarse step size but I would be cautious and start 'small' and increase gradually to ensure you get sufficient change in HFD for the process to work and generate the 'U' curve. As I said it all comes down to your particular gear ratio. My belt system is approximately 20:1 - I think. With my Fine step of 13 I can barely see the focus ring move - with the Coarse step of 26 I can clearly see a small movement.

If you set 'Reverse' the routine should (hopefully) initially drive the focuser away from the 'infinity' point - toward '10' or '5', and then step back gradually to go through the minimum point.

Good luck.

[Astro_Chroma]

This thread has been SO HELPFUL for me. THANK YOU.

I am currently putting together my Samyang 135mm for wide field astrophotography as well. I purchased the Hyperpod. While it is a great design, the guide shoe mounts are not sturdy and both snapped while I was barely tightening the screws to hold my guide scope and ASIAir Plus. To fix this issue with the guide shoe mounts for the guide scope, and ASIAir Plus, I used the guide shoe from the ASIAir Plus and EAF bracket that came with the EAF to secure it to the HyperPod. It works flawlessly (see attached pictures).

• You can still use the screws that came with the HyperPod.
• For the EAF bracket, you will the need a medium size washer to secure one screw to one end of the HyperPod mounting rings. Same thing for the ASIAir guide shoe mount, but no need for a washer to secure the guide shoe to one end of the mounting rings.
• The EAF bracket used with the ASIAir secured to the HyperPod mounting ring clears the large gear on the lens, and it is very sturdy once every thing is tightened up.

 

Regarding the EAF backlash, I currently have my set at 150; step limit is 6900; course step is set at 50 (will decrease this to 20-25 for fine step).

• To ensure the larger gear on the lens doesn't hit the EAF bracket, first adjust the lens so that infinity simply is 90 degrees and perpindicular to the large gear (and vise versa). 
• Set the lens to infinity and EAF "current position" to zero. 
• Run the EAF (starting at zero). Pay attention to the large gear and watch it approache the side of the EAF mounting bracket. Be sure to immediately stop the EAF before it hits the bracket. When stopped, jot down the EAF position, and set the position as your limit to ensure the large gear on the lens never hits the EAF bracket and cause the gear to skip.

The way I have my EAF positioned on the Hyperpod, I run the EAF in reverse (as suggested by Adrenaline). See attached pictures.

Regarding OSC spacers/adapters, I really like the Play One Poseidon-C Pro (IMX 571 sensor). Though, I would be switching to NINA to use this camera as it is not compatible with the ASIAir (duh...🙄). If I were to go with a ZWO camera, I think either the 533 but more so the 2600mc pro (which is comparable to the Poseidon) would be best as I want to utilize a large fov for widefield imaging. This dilemma is driving me crazy as I am also considering an astro-modified Canon RP. Any input would be helpful.

 

Regarding back focus (44mm required for the Samyang):

• For the Asi533mc pro : 6.5 (camera) + 11mm (adapter) + 26.5 (ZWO t2 thread to canon eos ef mount (without 5mm spacer) + .67 (2" filter -1/3 of the filter) =44.67 back focus.
• For the Asi2600mc pro or Player One Poseidon: 17.5(camera)+ 26.5 (ZWOt2 thread to canon eos ef mount without 5mm spacer) + 2" filter = 44.67
• If you decide to use a filter wheel with any OSC (such as asi533 or 294) with a 6.5 back focus to sensor I believe it replaces the 11mm. 

I think you're able to go over the standard back focus of 44mm with the Samyang by bit, as the ZWO t2 adapter for the lens intended for users to use a 2" filter.

I hope this helps.

 

 

 

 

 

Edited July 25, 2023 by Astro_Chroma