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Imaging with the Samyang 135mm f2


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17 minutes ago, Adreneline said:

Is that also the case when you use the lens on a Canon dslr?

I just used it once with the 600D and the focus point was at the very end of the L. Then changed to the M48 adapter + EFW + 294MM and had to remove the stopping screw to reach focus.

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I did post this 2 panel done with Paul Kummer and Peter Woods on the DSI board but here it is for Samyang lovers.

Wide open at F2, the Blue Horsehead region.

BlueHorsewide2panelcompositeweb.thumb.jpg.1445154ce9f3368e1177dd811afa059a.jpg

This Lens, the small pixel CMOS camera and Russ Croman's software come together with a sweetness rarely experienced this side of heaven! :grin:

Olly

 

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9 hours ago, Adreneline said:

Hi Pete,

In my opinion this is essential. I used my SY135 with my Canon 6D in January this year and took a photo of the focus position after using the autofocus routine in the ASIair and checking with a BM, this was the result:

IMG_5065.thumb.JPG.530eb6261d65d85fb6373bcf78e7e897.JPG

No two lens are identical, no two cameras are identical. The back focus of the cameras themselves is subject to a manufacturing tolerance so in the case of a ZWO camera you cannot be sure it is spot on 6.5mm. I fail to understand how some people state the definitive spacing is 44mm (say) for the SY135 when used with a ZWO camera. Filter thickness will have affect the spacing. I use 1mm Astronomik filters so in theory they affect the spacing by ~0.33mm.

Haha! You would like to think so! Again, this is my opinion only, but the SY135 is a consumer dslr lens not a dedicated astrograph. If you are lucky it will be a good one. (I recently bought a dedicated astrograph lens which had been tested prior to despatch but it still didn't perform as one would expect; I am awaiting a replacement).

Well mine is! I guess it comes down to the quality of the flats.

This is my current setup - I've been through so many iterations and variations I've lost count.

I am sure there is no misalignment or droop and the NB filters I use focus in the middle of the 'L' and I still have a slightly dodgy corner. It is what it is and I am happy :) 

IMG_5599.thumb.jpg.177572939c2db792e11397033fda719c.jpg

IMG_5600.thumb.jpg.33da507a6aaebde48411c185bdb8e637.jpg

HTH

Adrian

P.S. I am also a firm believer in using a step-down-ring and not using the aperture control on the lens. I use a 49mm sdr so the lens operates at about f2.6 and you don't get facets around the stars.

 

 

Think I might try my 600D with the Samyang & ASI Air Plus and make a note of where it focuses.

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24 minutes ago, SAW said:

Think I might try my 600D with the Samyang & ASI Air Plus and make a note of where it focuses.

An excellent idea.

I used my 6D+SY135 in January but never got around to looking at the subs I took of M42 - they are still residing on my old ASIair Original - 20s, 40s and 60s subs - 86 of them!

I've just loaded one of the 40s subs into Siril to look at the tilt - if any - and this is the result:

Screenshot2023-05-30at20_54_04.thumb.png.9d7f925de04534394927e13feb399386.png

The same analysis from ASTAP:

Screenshot2023-05-30at21_01_34.thumb.png.3c636074bf99f590c7e787c7e9e13f6f.png

This all looks very good but close inspection of the subs might suggest the lens is very slightly too close to the sensor:

Screenshot2023-05-30at21_04_15.thumb.png.e81663871917e3d6eaadf9cf62897101.png

All of this does make me think I still have a tiny amount of tilt in my SY135+ASI183 image train :( 

I have found in the past that not all M42 extension tubes are "perfect".

Hope this is of interest.

Adrian

 

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11 hours ago, Adreneline said:

Hi Pete,

In my opinion this is essential. I used my SY135 with my Canon 6D in January this year and took a photo of the focus position after using the autofocus routine in the ASIair and checking with a BM, this was the result:

 

No two lens are identical, no two cameras are identical. The back focus of the cameras themselves is subject to a manufacturing tolerance so in the case of a ZWO camera you cannot be sure it is spot on 6.5mm. I fail to understand how some people state the definitive spacing is 44mm (say) for the SY135 when used with a ZWO camera. Filter thickness will have affect the spacing. I use 1mm Astronomik filters so in theory they affect the spacing by ~0.33mm.

Haha! You would like to think so! Again, this is my opinion only, but the SY135 is a consumer dslr lens not a dedicated astrograph. If you are lucky it will be a good one. (I recently bought a dedicated astrograph lens which had been tested prior to despatch but it still didn't perform as one would expect; I am awaiting a replacement).

Well mine is! I guess it comes down to the quality of the flats.

This is my current setup - I've been through so many iterations and variations I've lost count.

I am sure there is no misalignment or droop and the NB filters I use focus in the middle of the 'L' and I still have a slightly dodgy corner. It is what it is and I am happy :) 

 

 

HTH

Adrian

P.S. I am also a firm believer in using a step-down-ring and not using the aperture control on the lens. I use a 49mm sdr so the lens operates at about f2.6 and you don't get facets around the stars.

 

 

Hi Adrain, thanks and that helps a lot. I've just run a pic through ASTAP and I have 24% tilt with the Poseidon-C. Good news since things can only get better. Think I'll go down the Astro Essentials Samyang Lens to M48 adapter route then shim the back focus so it's in the "L". I've also just put my SY lens on a Cannon  600D and it focuses inside the L. Both my cooled cameras are way outside. Looks like the 44mm backfocus on these lenses is a ballpark figure when used with astro cameras. Interesting you have no tilt when using a Canon camera! Again thanks.

6 hours ago, ollypenrice said:

I did post this 2 panel done with Paul Kummer and Peter Woods on the DSI board but here it is for Samyang lovers.

Wide open at F2, the Blue Horsehead region.

 

This Lens, the small pixel CMOS camera and Russ Croman's software come together with a sweetness rarely experienced this side of heaven! :grin:

Olly

 

Hi Olly, are you suggesting that this lens performs better with a small chip camera?

Clear skies
Pete

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9 minutes ago, Petrol said:

Think I'll go down the Astro Essentials Samyang Lens to M48 adapter route then shim the back focus so it's in the "L".

Just for the record I use the AstroJolo adapter which provides an M42 thread rather than M48; not sure it is still available but this is a possible alternative. The ZWO 1.25" EFW has an M42 thread either side and I prefer to have the EFW right up against the camera although I do use a shim at this interface to ensure I can achieve a 'landscape' orientation for my camera sensor.

Adrian

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Hello everyone! I generally hang out on cloudynights but this thread is far more active than anything I've found over there so I thought I'd hop across the pond for a bit of advice. I recently got a Samyang 135 and I'm attempting to pair it with a Poseidon C.  My first tests have not gone very well. I'm using an EF version of the lens with a ZWO Canon bayonet/filter drawer.  I've shimmed the bayonet adapter to a very tight fit with no obvious play when applying pressure.  I started with a backspacing of 44.6mm since I'm using a 2mm thick optolong UV/IR filter. With the lens pointed to zenith to rule out tilt from droop I was getting very poor stars in all corners. I tried f/2.8 to no avail.  I'm curious if people also account the for optical length added by the protective windows on their cameras?  The Poseidon has a 2mm thick window so my plan on the next clear night was to start with ~45.3mm of backspacing (44 + 2/3 +2/3) to account for the 2mm thick UV/IR and the 2mm protective window then start adding/subtracting 0.1mm spacers.  I've removed the hard stop for ease of use with my autofocuser.

The attached photo is not a test at zenith but is a few hours on the Iris.  As you can see I've got some fairly severe blue bloat as well. I'm hoping the spacing will help this also

Thanks!

Mike

Screenshot 2023-05-30 222236.jpg

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9 hours ago, Petrol said:

Hi Adrain, thanks and that helps a lot. I've just run a pic through ASTAP and I have 24% tilt with the Poseidon-C. Good news since things can only get better. Think I'll go down the Astro Essentials Samyang Lens to M48 adapter route then shim the back focus so it's in the "L". I've also just put my SY lens on a Cannon  600D and it focuses inside the L. Both my cooled cameras are way outside. Looks like the 44mm backfocus on these lenses is a ballpark figure when used with astro cameras. Interesting you have no tilt when using a Canon camera! Again thanks.

Hi Olly, are you suggesting that this lens performs better with a small chip camera?

Clear skies
Pete

No, with a small pixel camera. You can get a decent pixel scale from 135mm if your pixels are small enough. Our chip is the 2600.

Olly

 

Edited by ollypenrice
typo
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5 hours ago, TossJay said:

The Poseidon has a 2mm thick window so my plan on the next clear night was to start with ~45.3mm of backspacing (44 + 2/3 +2/3) to account for the 2mm thick UV/IR and the 2mm protective window then start adding/subtracting 0.1mm spacers.  I've removed the hard stop for ease of use with my autofocuser.

Hi Mike. Sounds like a good plan - I have no experience of the Poseidon camera so cannot offer any advice. Finding the correct spacing with the SY135 is all about well informed trial and error - and patience! Hopefully a Poseidon user will pop up and offer some first hand help. Good luck.

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23 hours ago, TossJay said:

Hello everyone! I generally hang out on cloudynights but this thread is far more active than anything I've found over there so I thought I'd hop across the pond for a bit of advice. I recently got a Samyang 135 and I'm attempting to pair it with a Poseidon C.  My first tests have not gone very well. I'm using an EF version of the lens with a ZWO Canon bayonet/filter drawer.  I've shimmed the bayonet adapter to a very tight fit with no obvious play when applying pressure.  I started with a backspacing of 44.6mm since I'm using a 2mm thick optolong UV/IR filter. With the lens pointed to zenith to rule out tilt from droop I was getting very poor stars in all corners. I tried f/2.8 to no avail.  I'm curious if people also account the for optical length added by the protective windows on their cameras?  The Poseidon has a 2mm thick window so my plan on the next clear night was to start with ~45.3mm of backspacing (44 + 2/3 +2/3) to account for the 2mm thick UV/IR and the 2mm protective window then start adding/subtracting 0.1mm spacers.  I've removed the hard stop for ease of use with my autofocuser.

The attached photo is not a test at zenith but is a few hours on the Iris.  As you can see I've got some fairly severe blue bloat as well. I'm hoping the spacing will help this also

Thanks!

Mike

Screenshot 2023-05-30 222236.jpg

I don't think it's a back spacing issue, it actually seems pretty good. What you have is coma, and that's a defect in the lens itself. I haven't seen that much coma in my own lens, so I wonder if you haven't got a bad copy. Samyang/Rokinon lens have a bad rep when it comes to quality control, and some people have noticeably better lenses than others

Here's an old shot with my Samyang and an APS-C camera, there's much less coma, if any!

image.png.57f00359d7d819dd7e2e68ce37aa495e.png

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On 01/06/2023 at 00:13, Space Oddities said:

I don't think it's a back spacing issue, it actually seems pretty good. What you have is coma, and that's a defect in the lens itself. I haven't seen that much coma in my own lens, so I wonder if you haven't got a bad copy. Samyang/Rokinon lens have a bad rep when it comes to quality control, and some people have noticeably better lenses than others

Here's an old shot with my Samyang and an APS-C camera, there's much less coma, if any!

image.png.57f00359d7d819dd7e2e68ce37aa495e.png

I would be pretty happy if I could get my stars to look like that at f/2.  I did some testing last night. at ~f/2.5  The 45.3mm backspacing did not help at all so I decided to start over at 44mm then add 0.1mm incrementally. 44mm was better than 44.6mm but still not great.  At 44.1mm I noticed that the pattern of aberration followed the sensor rotation so I stayed at 44.1mm and tried to work on tilt and spacing with NINA's aberration inspector and the camera's tilt plate.  The process is tedious since each run takes about 5 minutes, but if I watch the 9 panel aberration inspector during the autofocus runs I see that all 9 panels come to sharp focus at some point though not simultaneously.  So it seems the lens may be capable of giving a flat field but I'll probably need to spend another hour or two slowly creeping up on the ideal tilt and spacing.  I've got another two weeks to evaluate the lens before my return/replace window closes. If I can get it close I think blurxterminator ai3 should be able to take care of the rest.

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Used my 600D with the Samyang last night. Just a few 10s subs stacked of M86, no flats hence the vignetting. Stars are still poor in the corners. Was at f/2.8/

M86.jpg

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This is where my focus point is using the 600D and Samyang according to my ASI Air Plus, is this where I need my focus to be correctly spaced when using my 2600MM ?

PXL_20230603_115513055.MP.jpg

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8 hours ago, SAW said:

This is where my focus point is using the 600D and Samyang according to my ASI Air Plus, is this where I need my focus to be correctly spaced when using my 2600MM ?

 

That's exactly what I have done following Adrenelin's advice and it's made a massive difference.

Clear skies
Pete

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A small break in the clouds allow me to test my recently acquired narrowband filters (Baader 6.5nm SHO 31mm unmounted). However, results seem not very promising... I already had the H-alpha filter and it worked perfectly but:

  1. They are supposed to be parfocal but focus position is quite different from H-alpha to S2/O3.
  2. Transmission from H-alpha is what it is expected but S2/O3 signals are very weak.

One example from yesterday night: single uncalibrated 300s subs with ASI183MM Pro @ -10ºC gain 111 and the Samyang 135 ~f2.7 (using a 49mm step-up ring).

screenshot.thumb.jpg.d67c5c4d4edbc7c94a7bdd48c9157d17.jpg

So...

  1. May I have gotten defective filters, from different batches? Serial and part numbers seem fine but not having the same focus position worries me.
  2. May I have done an incorrect installation in the filter wheel? I don't think so, H-alpha works fine and S2/O3 are mounted identically, I even double checked which is the correct side.
  3. May I have issues due to band shift as I'm using a faster focal ratio (~f2.7) than the filter specification (>f3.4)? I'm aware of preshift filters but I read that band transmission loss is "acceptable" with the Samyang @ f2.8. I am wrong? Is this valid for H-alpha but not for S2/O3?
  4. Is everything OK but I'm just using very little integration? I expect more signal in S2/O3 despite being just one single 300s sub.

Weather is awful so I don't expect having a chance to test them again in the next days. Any help is welcome. This Samyang 135 is driving me crazy, specially due to bakcfocus and tilt problems, so adding one more issue is tempting me to sell it and buy a proper scope :(

Edit: I just added a pic comparing Ha and S2 subs using the same focus position at 100% magnification.

screenshot-focus.thumb.jpg.326e2e78af8b3cbd325de9bb87a1a9d0.jpg

Edited by aleixandrus
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You will experience some signal loss by not using a pre shifted filter, though I think it might be mitigated somewhat due to the speed of the lens. Your SHO signal will vary depending on your target, O3 is typically the weakest and can also be affected by moonlight. Out of curiosity, how is your O3 filter compared to the rest in terms of tilt or edge star distortion, I've experienced this with both the standard and fast speed filters, it can't be the image train as HA and S2 don't show the same issue.

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1 hour ago, aleixandrus said:

results seem not very promising...

I've recently imaged NGC7000 with my SY135+ASI183MM - 300s subs using Astronomik 6nm filters and this is a comparison for you with one single sub from each session:

Screenshot2023-06-05at13_33_27.thumb.png.38df804d600d9c6e7f309fbaf8290771.png

Difficult to tell but you do seem to have a little less O and S compared with H (and with my filters).

My H and S focus in almost the same position - O is a little different but not that much.

I also image at ~f2.6 using a 49mm sdr - gain was 111 and temp was -20 degrees.

"This Samyang 135 is driving me crazy, specially due to bakcfocus and tilt problems, so adding one more issue is tempting me to sell it and buy a proper scope :("

It took a while to get mine up and running properly and a lot of patience with assembling and disassembling to get spacing and tilt issues sorted - it was worth it in the end.

As for buying a proper scope - my experience of so-called 'proper scopes' has not been that great.

Adrian

 

Edited by Adreneline
Clarification and more detail
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20 hours ago, aleixandrus said:

Is everything OK but I'm just using very little integration? I expect more signal in S2/O3 despite being just one single 300s sub.

Was the moon out during capture?  Could the weather still have had some lingering impact?  I'd hold off making any permanent decisions until you've had another test or two. 

Like @Adreneline my Ha and SII are almost identical in focus as they are both in the red, but I still refocus when changing.  My OIII is different.  This seems standard where the R and GB focus positions are off on the Samyang.  I may have shown this before, but below was a test I made a while back, this was focused for OIII then switched through the RGB filters:

image.png.b1c5af8affdede92e72e2ec5376a7171.png

20 hours ago, aleixandrus said:

May I have issues due to band shift as I'm using a faster focal ratio (~f2.7) than the filter specification (>f3.4)?

Perhaps, but with slightly wider filters and stopping down the lens, maybe not too much.  

Edited by geeklee
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19 hours ago, Elp said:

You will experience some signal loss by not using a pre shifted filter, though I think it might be mitigated somewhat due to the speed of the lens. [...] Out of curiosity, how is your O3 filter compared to the rest in terms of tilt or edge star distortion.

Well loss some signal and not taking fully advantage of the f2 ration is what I hoped. Right now, it makes not sense to me buy some of those expensive 'highspeed' filters because my next rig will be (probably) a more traditional 80/90mm 'slow' refractor.

Regarding your question, corner stars are not worse in O3 than Ha... but my image train has significant issues with backfocus and tilt, specially in one corner, so possible issues due to the O3 filter are completely invisible.

 

19 hours ago, Adreneline said:

I've recently imaged NGC7000 with my SY135+ASI183MM - 300s subs using Astronomik 6nm filters and this is a comparison for you with one single sub from each session:

My H and S focus in almost the same position - O is a little different but not that much.

Thank you! Very illustrative, this gives me a good view on how my subs should be. Those Astronomik filters are the "MaxFR" or the traditional ones?

 

3 minutes ago, geeklee said:

Was the moon out during capture?  Could the weather still have had some lingering impact?  I'd hold off making any permanent decisions until you've had another test or two. 

Like @Adreneline my Ha and SII are almost identical in focus as they are both in the red, but I still refocus when changing.  My OIII is different.  This seems standard where the R and GB focus positions are off on the Samyang.  I may have shown this before, but below was a test I made a while back, this was focused for OIII then switched through the RGB filters:

image.png.b1c5af8affdede92e72e2ec5376a7171.png

Yeah, the weather was awful and there was moon. I know they are not the best conditions to test the filters but it was rainy and cloudy for 2 months and the prediction for the next weeks is similar. But I needed to test the filters before the ending of the refund window... I know I need more tests and I don't want to return them (I was very happy with my Baader Ha) but I also need to know if I'm doing something wrong...

Regarding focus position, I don't get your point... Despite R and GB focus are of on the Samyang, when shooting mono this should not have major impact. Although refocusing after filter swap is a good idea, if filters are parfocal focus position should be similar anyway, at least with narrowband filters. Based on your star diffraction patter, they are (well, somehow). But check how are the stars in my second picture... they are not in close focus but no means! In fact, using my EAF, based on my tests I achieve focus in the ~6500 position for Ha and ~6600 position for S2/O3, which are a lot of motor steps. I'm missing something?

 

For the moment, I think I should:
1) More text with better forecast and more integration time.
2) Stop down the lens to f4 to discard band shift issues.

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36 minutes ago, aleixandrus said:

Yeah, the weather was awful and there was moon. I know they are not the best conditions to test the filters but it was rainy and cloudy for 2 months and the prediction for the next weeks is similar. But I needed to test the filters before the ending of the refund window... I know I need more tests and I don't want to return them (I was very happy with my Baader Ha) but I also need to know if I'm doing something wrong...

Definitely understandable that you want to get basic tests done.  Given the moon and weather it's difficult to compare to others.  I can't see anything obvious you're doing wrong given the checks you listed.

37 minutes ago, aleixandrus said:

Regarding focus position, I don't get your point... Despite R and GB focus are of on the Samyang, when shooting mono this should not have major impact.

The filters may be parfocal but the Samyang lens is not bringing all wavelengths of light to focus at the same point.  

38 minutes ago, aleixandrus said:

if filters are parfocal focus position should be similar anyway, at least with narrowband filters. Based on your star diffraction patter, they are (well, somehow).

Similar perhaps, but as I understand it, it depends how well corrected the scope/lens is.  In my image, the red may look "a little off" but it looks noticeably out of focus if I was to shoot my Red/Ha at that focus point.  Likewise, if I have focused for Ha, the OIII will be out of focus.  I see the symptoms of this when shooting OSC on my Samyang.

42 minutes ago, aleixandrus said:

In fact, using my EAF, based on my tests I achieve focus in the ~6500 position for Ha and ~6600 position for S2/O3, which are a lot of motor steps. I'm missing something?

I'm not sure why this is, sorry.  Good idea, trying F4 for focus position although gauging signal gain/loss will be more difficult. 

My Ha and OIII are at least 100 steps apart I'm sure.

I can only suggest to test further where possible and refocus between filters (any filters) and then compare.  

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Last night I just experimented with trying to get the correct focus postion with my 2600MM so it would focus in the same postion as it did with the 600D. With the correct spacing it would focus way past the bottom of the L mark, even just adding 1mm of spacing then through the focus back the other way where it was in focus before the L mark.

It's a pain trying to get it adjusted as I am using the Astrodymium mount so I have to strip eveything off just to adjust the spacing !

Wondering if I could try it in the daytime on something far away ?

Going to give it one more try then I'll be changing it to a small wide refractor.

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Rigging method helps. I just use lens rings so it's easy to screw the camera end off and adjust spacing, also lens rotation is easy. And I usually use two lenses at once so have to setup, orient, align one lens to the other, focus manually with each before imaging. Its not really an issue for me because of how I've made my rig which I've spent a while chopping and changing to how it is now.

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