Widefield Astrophotography with the Samyang 135mm f/2 Lens
If you are thinking of getting into astrophotography, then the Samyang 135mm f/2 ED UMC prime DSLR lens should be near the top of your shopping list.
The 135mm focal length (which is wide in astronomy terms) will allow you to capture impressive images of larger nebulae and deep-sky objects whilst short enough to make tracking manageable, even with a simple star tracker mount.
The high-quality optics produce a truly flat field, giving you crisp, sharp stars right to the corner of the imaging frame, even on full-frame sensors.
One of the best features of this lens is its massive f/2 maximum aperture, which will allow you to capture lots of light.
You will be able to capture fantastic astrophotography images with only a couple of hours of total exposure time, which is invaluable if you have limited time or struggle to find a clear weather window.
In this post, I will share why I think this lens is excellent for astrophotography, along with some tips on how to get the best out of it. Throughout the post, I have included sample images that I’ve taken with this lens for you to enjoy.
Contents
1. Features
2. Build Quality
3. Field of View
4. Deep Sky Targets
5. Focusing
6. Field Flatness
7. Vignetting
8. Diffraction Effects
9. Summary
Features
The Samyang 135mm f/2 (also known as the Rokinon 135mm f/2 in the United States) is a fully manual prime lens, but don’t be put off by the lack of auto-focus or the manual aperture setting; astrophotography does not require these features to be automated.
Inside the lens are 11 lens elements arranged in 7 groups, all working together to produce a sharp, flat field with minimal distortion, critical for creating high-quality astro-images. Below is the optical arrangement of the lens elements.
The lens contains one element of Extra-low Dispersion (ED) glass. This ED element ensures that light at both the red and blue ends of the spectrum come into focus together, minimising chromatic aberration, and keeping the bright stars in your images free from distracting colour fringing.
Every lens element has had an anti-reflection coating applied to both sides. This is what Samyang call Ultra Multi-Coated (UMC). The anti-reflection coatings maintain high transmission levels right through the lens and reduces unwanted back reflections, which can cause ghosting or halos around stars.
With a clear aperture of 67mm, the lens is comparable to a small refracting telescope in terms of light capturing ability and lens resolution. It also has a standard 77mm filter thread should you wish to use standard photography filters.
North America and Pelican Nebula in Cygnus taken with the Samyang 135mm F/2 lens, by Mike Soulby © stellardiscovery.com
The outer diameter of the lens is 82mm and comes with a cylindrical lens hood, which slots cleanly onto the end. With the lens hood fitted, the outer diameter increases to 93mm.
The lens hood does a good job at reducing stray light, helping to maintain contrast in your images, but it also acts as an effective dew shield allowing you to image for longer if the temperature drops below the dew point.
Available for several camera systems, the lens is very accessible, and if you already own a DSLR, there is likely a version to fit your existing kit.
Lens systems supported, find your camera type below: Canon EF, Fujifilm X, Nikon F (FX), Pentax KAF, Sony Alpha, and Sony E
| Canon | Nikon | Fuji X | Sony E | Sony Alpha |
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One thing to be aware of is that there are no electronics in the lens to tell the camera what lens is attached or how it is set, for example, the focal length or aperture setting. This means that your photo’s EXIF data will not include any information and will need to be added manually.
Specifications
| Description | Specification |
|---|---|
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Model Name |
Samyang 135mm f/2 ED UMC |
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Aperture Range |
f2 to f22 |
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Aperture Diaphragm |
9 Circular Blades |
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Clear Aperture Diameter |
67mm |
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Filter Thread |
77mm |
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Outer Diameter |
82mm |
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Field of View (APS-C) |
10.4° x 6.9° (12.4° Diagonal) |
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Field of View (Full Frame) |
15.5° x 10.6° (18.8° Diagonal) |
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Weight |
830g |
| Description | Specification |
|---|---|
|
Model Name |
Samyang 135mm F/2 ED UMC |
|
Aperture Range |
F2 to F22 |
|
Aperture Diaphragm |
9 Circular Blades |
|
Clear Aperture Diameter |
67mm |
|
Filter Thread |
77mm |
|
Outer Diameter |
82mm |
|
Field of View (APS-C) |
10.4° x 6.9° (12.4° Diagonal) |
|
Field of View (Full Frame) |
15.5° x 10.6° (18.8° Diagonal) |
|
Weight |
830g |
Build Quality
My first impressions of the Samyang 135 mm f/2 are that this is a solid, well-built lens. It is also quite heavy (830g) due to the 11 lens elements inside. The lens arrived well-packaged and also included a cylindrical lens hood and a soft carry bag.
The Samyang 135mm f/2 is built using a combination of metal and textured plastics. The materials are high quality, and overall the lens feels like it has been well put together. Even after a thorough examination, I could find no noticeable rattles or flaws.
The focus ring is nice and wide, which I find is essential for a manual focus lens. It is easy to find and grip when you are trying to focus in the dark. The focus ring has a soft textured rubber grip, and the motion is smooth, offering a good amount of resistance, making fine focusing easy.
Once in focus, there is no slop in the final position, and your stars will remain sharp and in focus.
The large focusing ring on the Samyang 135mm F/2 lens makes focusing in the dark effortless.
Aperture adjustment on the Samyang 135mm f/2 is also fully manual; however, this is not a problem for astrophotography as you will tend to stick to one aperture setting for your entire session. You may wish to stop down to f/2.8 or f/4 once you have found focus, but more on this later.
The aperture adjustment ring is located close to the lens mounting ring, so it can feel a little close to the camera body when adjusting. The aperture setting dial clicks nicely from f/2 through to f/22. Each f-stop has an obvious click and position and is unlikely to be displaced unintentionally.
One thing I find fiddly is putting the lens cap back on to shoot dark frames, especially with the lens hood fitted, or if my hands are cold. It can often take several attempts to attach it properly, so something to watch out for.
Flaming Star Nebula (IC405) and Tadpole Nebula (IC410) in Auriga is another great target for the Samyang 135mm f/2 lens, by Mike Soulby © stellardiscovery.com
Field of View
The Samyang 135mm f/2 lens is very wide in astrophotography terms. Most small refracting telescopes start in the 300 to 400 mm focal length range, and even these are classed as widefield telescopes.
When attached to a DSLR camera with a full-frame sensor, the lens offers a massive 15.5° x 10.6° field of view, or 18.8° across the diagonal. Even on an APS-C cropped sensor, common in entry-level DSLRs, the lens still provides a wide view of 10.4° x 6.9° (12.4° diagonal).
To give you an idea of what the Samyang 135mm f/2 can capture within a single frame, see the simulated field of view of Orion below for both the APS-C and Full Frame sensors.
Field of view simulation in Stellarium is a great way to frame up your target in advance.
It is possible to capture all three stars in Orion’s belt, the horsehead and flame nebulae, the reflection nebula M78, and the great Orion nebula M42 in just one shot. If you have a full-frame sensor, you can even squeeze the Witches’ Head Nebula into the frame too.
Setting up your expected field of view in astronomy software, such as Stellarium, is a great way to help you plan, select, and frame your astrophotography targets before the real thing. It can really help you save time when under clear skies if you know what you are shooting and how you want to shoot it.
The wide field of view of the Samyang 135mm f/2 lens gives you a lot of freedom to play with the image composition and framing. Below is the image I shot of the same area in the Orion constellation using a DSLR with an APS-C sized sensor. This has been cropped to help show off the Horsehead and Flame Nebulae, and the Great Orion Nebula together.
Widefield image of Orion’s Belt and Sword was taken using the Samyang 135mm f/2 lens, by Mike Soulby © stellardiscovery.com
It is possible to capture an impressive amount of detail with this lens; below is a zoomed-in version of the above image, allowing you to see the detail of the dark horse’s head and the darker areas within the Flame Nebula more clearly.
Cropped images contain impressive details, such as this crop of the Horsehead and Flame Nebula, by Mike Soulby © stellardiscovery.com
This is just one example of what this lens is great at, capturing impressive detail of large deep-sky objects and the surrounding star fields.
Deep Sky Targets for the Samyang 135mm f/2 Lens
Below is a list of some other DSOs that I think are perfect deep-sky targets for the Samyang 135mm f/2 lens.
- Andromeda Galaxy, our neighbouring galaxy, was my first deep-sky image taken using this lens and is a great target for beginners.
- Orion’s belt and sword, including the Horsehead + Flame Nebulae and the Great Orion Nebula.
- The Heart and Soul Nebula in Cassiopeia; with careful framing, it is also possible to fit the double cluster in Perseus into your view.
- North American and Pelican Nebula, another great choice for beginners, located close to the bright star Deneb, makes this an easy target to frame-up.
- Flaming Star Nebula in Auriga; a very interesting area of the night sky filled with open clusters, nebulae and colourful stars.
- The Cygnus Loop (Veil Complex); This supernova remnant is split into the Eastern Veil and Western Veil nebulae, but the Samyang 135mm f/2 lens will allow you to capture the whole thing. I would recommend a dual narrowband filter for this target, such as the L-eNhance filter by Optolong, to really help bring out the whispy details.
- The area around the star Sadr in Cygnus; a large area filled with diffuse emission nebula. If you have an astro-modified DSLR, this is a great region to capture in late summer or early autumn.
- The Witches’ Head Nebula; a great choice near the bright star Rigel in Orion. This reflection nebula is an ideal target for an unmodified DSLR camera.
- Rosette Nebula in Monoceros, a large target that is best shot from January to March, the wide field of view will also allow you to capture the Cone Nebula and Christmas Tree Cluster in the same frame.
Focusing
Achieving pin-point star focus on the Samyang 135mm f/2 is simple.
One of the easiest ways to focus is to use the camera’s live view feature. This way, you get to see exactly what your camera sensor sees, plus it is quick, simple, and doesn’t need any additional equipment or software.
The magnificent Andromeda Galaxy (M31) is a great first target for the Samyang lens, by Mike Soulby © stellardiscovery.com
To achieve pin-point star focus, follow these easy steps:
1) Set the focus ring at infinity and set the aperture setting wide open, i.e. f/2. Setting the lens to infinity will bring you into the correct range for focusing on stars, and only small refinements will be needed from here.
2) With the live view feature enabled, move your mount to find and centre a bright star.
3) Once centred, use the digital zoom feature, which will enlarge a small area of your live image to either x5 or x10 magnification. You may need to reposition the star to the centre of the view when you do this using your camera’s arrow keys. Once centred and magnified, you can begin to refine the focus.
4) As you adjust the focus ring, the aim is to make the star as small as possible. You will need to move in and out of focus a few times to help you decide when the star is as small as you can make it; see the image sequence below for an illustration.
As you approach the focal point, you may start to see fainter stars pop into view; this is a good indication you are on the right track.
5) You should now be in focus! To guarantee that you are well within the focus sweet spot, you can stop down the lens to f/2.8 or f/4. This will give you a wider depth of field, but more importantly, it reduces the chance that your camera will drift out of focus as the temperature changes through the night.
I find this focusing method a very quick and reliable way to focus the Samyang 135mm f/2 without needing any extra kit or a connection to a laptop. All of the images I have shared in this post were focused using this simple method.
This is by no means the only way to ensure sharp focus; you may wish to use a Bahtinov mask or even connect your camera to a laptop.
Many astrophotography imaging acquisition packages, such as the free Astro Photography Tool, include focusing tools that automatically measure the star’s width.
Field Flatness
The superb field flatness is one of the main reasons why astrophotographers love the Samyang 135mm f/2. The combination and quality of the optical elements produce a truly sharp flat field from corner to corner.
Stars in the corner of the frame are just as sharp and undistorted as those in the centre.
The image below is one 80 second sub-exposure of the Flaming Star Nebula region in Auriga, which I shot using the Samyang 135mm f/2. This sub-exposure has had some basic levels and curves stretches applied to make things a bit easier to see, but otherwise, this is straight out of the camera.
Zooming into the corner of the image, you see pinpoint stars, which is exactly what you want to see in astrophotography images.
Stars remain sharp even in the corners of your images.
The fully processed image of the above Flaming Star Nebula is included earlier in this post.
To get this level of performance from a lens at this price point is exceptional.
Vignetting
Vignetting is the darkening of an image towards the corners of the frame and is a common issue on fast (wide aperture) telephoto lenses. The Samyang 135mm f/2 lens is no different and suffers from significant vignetting at wide apertures.
In astrophotography, vignetting results in ugly gradients in the corners of your image, particularly when you stretch the image to pull out faint details.
These gradients can be dealt with effectively by using flat calibration frames in your image stacking process. I would absolutely recommend that you include them as they can make a big difference to your final image.
Below is a typical flat frame I shot on an APS-C sensor at f/2; this image has been stretched again for clarity, but the vignette gradient is clearly visible in the corners.
The Samyang 135mm f/2 lens does suffer from vignetting but can be dealt with by taking flat calibration frames.
It is possible to reduce the amount of vignetting by stopping down your aperture to f/2.8 or f/4. However, it is not possible to remove it completely and maintain a useful wide aperture for astrophotography.
Therefore, you should always aim to take flat frames to help remove corner gradients. Trevor at Astrobackyard.com has put together a nice post on how to take flat frames that is well worth a read through.
Diffraction Effects
Inside the Samyang 135mm f/2, there are nine precision rounded aperture blades, which closely approximate a circular aperture when combined. For daytime photography, this creates a beautiful bokeh effect of any objects out of focus.
As the aperture is not a perfect circle, the lens will produce diffraction spikes around the brightest stars in your image, and the effect becomes more apparent at smaller apertures.
Each aperture blade creates two diffraction rays 180 degrees apart, perpendicular to the edge of the blade. As there is an odd number of blades inside the lens, the 9 blades will produce 18 diffraction spikes in total.
Below is an example of this effect on bright stars. These two stars in the image are viewed at 100% zoom, and to highlight the effect, I have applied an aggressive curves stretch in photoshop.
Non-circular aperture diffraction spikes are noticeable on bright stars.
In reality, the effect is only visible around bright stars and is relatively small in its extent. The two stars shown above are the bright stars from my Horsehead nebula image shown earlier in the post, and in my opinion, this effect does not spoil the overall image.
If you wish to remove this effect altogether, the best way to do this is to shoot with the aperture wide open at f/2. In this situation, the aperture blades are recessed under the lens casing, producing a perfectly circular aperture and no diffraction spikes.
There is a trade-off when the aperture is wide open, you will have a very narrow depth of field, making your otherwise perfect focus more susceptible to temperature drift, and the strong vignette present at f/2 will need to be dealt with.
My preference is to set the aperture to f/2.8 with my APS-C sensor to make sure my focus is spot-on and remains stable even as the temperature changes through the night. I can live with the small diffraction rays around the brighter stars; in some cases, I even prefer it.
Summary
The Samyang 135mm f/2 DSLR lens is fantastic for astrophotography. When paired with a simple star tracking mount, this lens will transform your DSLR into a very capable and portable widefield astrophotography rig.
Ready to go! The Samyang 135mm f/2 lens on a Canon DSLR mounted to the Skywatcher Star Adventurer tracking mount, a very simple yet portable setup.
There are many positives to the Samyang 135mm f/2 lens; it has earned a solid reputation within the astrophotography community for producing high-quality astrophotography images.
Take a look through some of the community images at Astrobin and see what this lens is capable of.
You can find the latest price and availability of the Samyang 135mm f/2 on Amazon
| Canon | Nikon | Fuji X | Sony E |
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Pros
- A very fast lens with its f/2 maximum aperture – captures fantastic astrophotography images with only a couple of hours of total exposure time.
- Well built, with included lens hood (i.e. dew shield).
- 135 mm focal length provides a very generous field of view, great for capturing large deep sky objects.
- Flat field with minimal distortion even in the corners of the frame.
- Incredibly sharp images: achieve pin-point star focus.
- Very manageable on a simple star tracker mount, in ideal conditions with good polar alignment, expect to achieve 2 to 3 minute-long sub-exposures.
- Easy to focus
- Available for most DSLR cameras making the lens very accessible, even for beginners.
- Affordable
There are some negatives, but for the price point, I think these are minor issues when it comes to using this lens for astrophotography.
Cons
- Strong vignette at wide apertures, particularly on full-frame sensors.
- Diffraction spikes due to the approximately circular aperture. Can be eliminated by shooting wide open, but be careful of your focus and vignetting.
- No electrical connection to the camera – your image files will lack any focal length and aperture details.
I have not listed that the Samyang 135mm f/2 lens has manual focus or manual aperture settings as a negative; the lack of these features does not reduce the usefulness of the lens for astrophotography.
The Rosette and Cone Nebula in Monoceros is another interesting choice for the Samyang lens, by Mike Soulby © stellardiscovery.com
I use this lens all the time, and there are still many targets I want to try photographing with it. It is also very portable and can be taken to dark sky sites and set up with very little effort. If you are thinking of getting into astrophotography, then this lens should be given some serious consideration, well ahead of looking for a new telescope.
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17 Comments
Arie · October 25, 2021 at 2:11 am
Hi Mike
Thanks for a great article on the lens and it use, great pictures and list of targets.
Thanks
Arie
Mike_Soulby · November 2, 2021 at 10:25 am
Thanks Arie, I am glad you found it helpful.
Kathie · February 7, 2022 at 6:13 pm
Hi Mike, I just purchased the Samyang version of this lens to use on a Z6ii. Can you clarify – this lens can be used for simple astrophotography w/o any kind of tracking device? Also, what settings work to get results (ie. some of the nebulae you mentioned) It seems like one has to have a very short exposure before the star trails form. Photopills indicates probably < 2 secs. Thank you so much!
Mike_Soulby · February 12, 2022 at 9:03 pm
Hi Kathie,
Yes, it is absolutely possible to do this with short exposures. The key is to take lots of short exposures, perhaps upwards of 1000 or more. These photos are then stacked in a stacking program such as DeepSkyStacker .
Taking lots of photos improves the signal to noise ratio, this means you will be able to pull out more faint details of the deep-sky object when processing the image without the noise overriding the image.
You will be better off trying this first on some of the brighter deep-sky targets, such as the Orion Nebula (M42) or the Andromeda Galaxy (M31).
Some suggested camera settings:
– Set your ISO to about 1600 / 3200
– Set the maximum exposure according to the 1/500 rule or the NPF method outlined in Photopills for your camera and the Samyang lens’ focal length. This will be at most a couple of seconds before the stars will trail with this combination. It is best to take some test exposures to see if you are happy that the stars are not trailing excessively.
– I would keep the aperture wide as you want to capture as much light as possible, no smaller than f/4.0.
– To semi-automate taking this many images you will need an intervalometer that can connect to your camera. This handy gadget allows you to set your exposure length, the number of exposures, a short pause between each shot and allows you to be hands-free so you don’t have to keep pressing your camera’s shutter button. For the Nikon Z6 something like this https://amzn.to/3oIGrOS would probably be suitable, I have used a similar one successfully for my Canon 7D and 200D.
– Whilst you are taking the pictures you will need to periodically realign your tripod to keep up with the target. Try not to let the target move too far from the centre of your frame before you re-adjust so try to shoot in batches. The stacking software can handle the alignment of the individual frames so some movement between frames is OK.
Once you have all of your light frames (shots of the actual target) you will need to take some calibration frames: dark frames, flat frames and bias frames. These help to reduce thermal noise/hot pixels, gradients and camera read-noise respectively. You add all of these into DeepSkyStacker and it will help improve the final image by subtracting these noise artefacts from the stacked image. Once you have the stacked image you will need to open this in Photoshop to process and bring out all the faint detail in your final image.
Nico Carver at Nebulaphotos.com has a great video tutorial on exactly this subject of astrophotography with no star tracker. He goes into great detail from start to the final image, it is well worth checking out https://www.nebulaphotos.com/resources/m31/
This approach will hopefully get you started. Allowing you to capture some images of the brighter deep-sky objects. Once you get the hang of this and stacking images you will be ready to move to a star tracker where you will be able to reach sub-exposures of 2-3 minutes with the 135mm focal length.
Regards
Mike
Kathie O'Donnell · July 5, 2022 at 10:28 pm
Just wanted to thank you for your detailed reply. Found it today (late) as I have been ignoring the lens for awhile :). PhotoPills sure is an amazing app. Happy shooting!
Rod Henry · February 16, 2022 at 5:07 pm
Thanks for the review and the hints. I’m ready to buy one of these for my SONY cameras.
Mike_Soulby · February 16, 2022 at 8:35 pm
Thanks Rod, It’s a fantastic lens I am sure it will serve you well.
Scott Kuntz · May 7, 2022 at 12:19 am
I have purchased this lens and I have been testing it out. I am finding that the focus ring stop short of true infinity focus. Apparently this is a known issue. I can either send it back or remove the focus stop as described some places on the internet. Any insight or recommendations?
Mike_Soulby · May 10, 2022 at 9:25 pm
Hi Scott, thank you for your comment, I am sorry to hear that you having problems with your Samyang. I have not personally encountered this problem with the lens. I understand there may be a fix that you could try if you are comfortable with adjusting the lens yourself. However, if I encountered this issue of a lens not reaching infinity when attached to the DSLR camera model that it is designed to fit I would send it back for replacement or repair. I hope you are able to find a solution and are able to start using this wonderful lens.
William Smith · May 7, 2022 at 10:56 pm
I am really new to astrophotography so buying equipment and software is a big issue. While there are many articles about how good this lens is I am having a hard time with making a decision. The Sigma 135mm F1.8 has much better specs then the Samyang but there are no reviews of the Sigma for astrophotography nor are there any comparisons of the two lens. Your thoughts would help me and perhaps encourage you to do a side-by-side comparison. I have a Sony a7R III, Fujifilm X-E4, and the Canon EOS M6 II so I need to have a lens that can be used on all three cameras. Both lens with the Canon EF mount will satisfy that problem.
Mike_Soulby · May 2, 2024 at 10:00 pm
I think the big appeal of the Samyang lens is its cost, it really is a great entry level lens for astrophotography. I have had a quick look at the Sigma lens and it looks like a very fine lens indeed, but I believe for astrophotography the Samyang will in many cases perform just as well or at least well enough for astrophotography, especially as there are bigger things to contend with, such as polar alignment and accurate tracking. If you need autofocus then the sigma would win all the time but if you are happy with manual focus, which for astrophotography is not really an issue then you will be able to capture many great images with the Samyang. I am sure there are others that think differently and I would love to do a side by side by side comparison, but alas astrophotography is an expensive hobby and I have my eye on some other bits at the moment ;-). Good luck with whichever lens you choose.
Electro · September 18, 2022 at 4:40 pm
Hello,
I have the same RIG (well not the camera) but i have a Canon EOS 2000D a Samyang 135mm f2 an a SkyWatcher SkyAdventurer 2i
But in this configuration I cannot balance the mount
…
Mike_Soulby · October 25, 2022 at 9:43 pm
The SkyWatcher Star Adventurer is designed for this kind of setup so it is possible to achieve good balance on the right ascension axis. A tip would be to move the bulk of your mass towards the centre of rotation. i.e moving the camera towards the middle, the closer you are to the centre means that you don’t have to move the counterweight so far out to balance the camera; there will be plenty of range for the counterweight to move to achieve balance. One thing to watch if you do this is you can block the polar scope so move the camera as far towards the centre without blocking it if you use it for polar alignment. Also, be careful of cables that might be pulling on the camera, as you rotate the setup check that these cables are able to move freely as the setup rotates.
Mark Poole · January 28, 2023 at 2:09 pm
I’d like to shoot at F/3.2 or F/4 to increase the depth of field but don’t want the diffraction spikes. Have you considered or tried a step-down ring for the aperture?
Mike_Soulby · May 2, 2024 at 9:36 pm
Its an interesting idea, not something I have tried. If you find the diffraction spikes really distracting on brighter stars it would be an option. I don’t mind them too much, but depending on the image I may want to open the aperture all the way to f2 to remove them and just spend a bit more time ensuring my focus is spot on.
Steve Heise · January 20, 2024 at 2:39 pm
I also have the issue with infinity focus and am going to do the adjustment. I just don’t understand with such a simple fix available, how it could come from the factory this way. It’s a well known issue.
Mike_Soulby · May 2, 2024 at 9:39 pm
I am sorry to hear you are having this issue with your Samyang lens. I am also surprised it would leave the factory like this. It is not something i have personally experienced but can understand your frustrations. At least there is a fix available to allow you enjoy the great optics.