Rokinon 135mm F/2 Review - A Must-Have lens for Astrophotographers
Updated: May 19, 2023
The Rokinon (Samyang) 135mm f/2 ED UMC lens is an affordable and fast telephoto lens that truly shines when used for astrophotography.
The lens can be used with both full-frame and cropped-sensor cameras and features a manual-only focus ring.
We've used this lens for astrophotography on both a mirrorless and a cooled astronomy camera and were incredibly impressed by its capabilities regardless of the target.
If you felt confused about the name of this lens, it may be because Rokinon and Samyang are two names for the same product. Essentially, it is both a Rokinon and a Samyang lens.
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Table of Contents
Introduction
What's in the Box?
Imaging Rho Ophiuchi in the Milky Way with the Rokinon 135mm f/2 lens
Rokinon 135mm f/2 Specs & Price
Lunar Photography with the Rokinon 135mm f/2 lens
Accessories - Astronetics mount & Astronomy camera adapter
Star Shapes at f/2
Imaging Winter nebulae with the Rokinon 135mm f/2 lens
A Great Lens for Small Constellations
Best Targets to Photograph with the Rokinon 135mm lens
Final Thoughts
Samyang 135mm f/2 - What's in the Box?
The lens comes in a nice box which you can see below. It is well-padded and full of technical information on the sides. If you ordered the Rokinon version, the box you would receive would be very similar and its contents identical.
Here is what is included with the Rokinon/Samyang 135mm f/2:
The lens
The lens front and rear caps
A lens hood
A carrying pouch
A warranty card for a 1-year warranty
The user manual
The lens hood attaches to the end of the lens and helps protect it from light reflections and dust. It is reversible, which is great because it allows you to easily pack the lens back into the pouch with the hood included. We suggest always using the lens hood to ensure you do not get flares while imaging. Another good point of this lens hood is that the end is flat, making taking flats using a flats panel or t-shirt at the end of the night very simple.
Imaging Rho Ophiuchi in the Milky Way with the Rokinon 135mm f/2 lens
Our first light with this lens was on the large molecular cloud complex known as Rho Ophiuchi. I imaged this target with a friend from a dark site in the California desert, using a mirrorless Canon camera and a German equatorial mount.
When shooting with DSLR lenses I usually like to keep it safe and bring the aperture down to around f/4. For most lenses, f/4 is considered the sweet number to have both a fast aperture and low risk when it comes to having round stars on the edges.
This time, I decided to go crazy and shoot wide open at f/2! Well, I was really blown away by the quality of the frames that came out of the camera. The stars looked nice all over the field of view, and there was no chromatic aberration or other visible problems that originated from the lens.
I used an ISO of 1600 and did 3-minute exposures at f/2, and that seemed to be a little bit too bright when looking at the histogram! An ISO of 800 or maybe even 400 might have been better in this case.
3 hours on Rho Ophiuchi from a dark site with the Rokinon 135mm f/2 lens
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GEAR USED:
Camera: Canon Ra
Lens: Samyang 135mm f/2
Mount: Motorized EQ-G
Power: Jackery Lithium Battery
Processing: Pixinsight
ACQUISITION DETAILS:
Total Exposure Time: 3 hours
Exposure Time per frame: 3 minutes
ISO: 1600
Specs & Price
The Rokinon 135mm f/2 is a manual focus lens made of high-strength aluminum alloy. It has a focal length of 135mm and a fast f/2 aperture. It can be used with both cropped sensors and full-frame cameras, and is described by the company as being a fantastic lens for shooting portraits, wildlife, and night sky photography.
General Specs
Focal Length: 135mm
Aperture Range: f/2 to f/22
Coverage: Full Frame
Optical Construction: 11 elements in 7 groups
Lens Length without hood: 122mm
Lens Length with hood: 179.6mm
Weight: 1.8 lbs (816 g)
The lens' full name is the Rokinon 135mm f/2 ED UMC. The "ED" means that it includes an extra-low dispersion lens for higher-resolution images. "UMC" stands for Ultra Multi Coating, which will reduce flares and ghost artifacts.
Not sure if this lens will work on your camera? Make sure it you have one of the following 9 camera mounts/adapters if you plan on adding this lens to your collection!
Canon EF
Nikon F
Pentax K
Sony A
Canon M
Fujifilm X
Samsung NX
Sony E
MFT
Pricing
The Rokinon and Samyang 135mm f/2 lenses are currently priced between $395 and $600 depending on the date. The price of lenses, telescopes, and other items have been varying a lot since COVID, so hopefully, it is closer to $400 when you decide to purchase it!
You can check the price of the Samyang lens today on Amazon. Be sure to compare with the Rokinon version as well to see which one has the better price! Remember, they're both the exact same lens!
A similar lens to this would be the Canon EF 135mm f2L USM, but we honestly don't think the Canon version is worth its higher price tag.
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Lunar Photography with the Samyang 135mm
Because 135mm is considered a telephoto lens, we wanted to see how this one would perform on the moon.
We attached the lens to our Canon 7D Mark II DSLR camera and aimed it at the half-moon. The result looks great, although it is of course not the most impressive moon you'll ever see because of how much cropping we had to do from the original picture.
Indeed, 135mm is not ideal for lunar photography as it is still too small. We recommend using a lens with a focal length of around 300mm if you plan on taking pictures of the moon with your DSLR camera.
The picture on the right shows the full uncropped image straight out of the camera, so that you can understand how the moon will look like through this 135mm lens and cropped-sensor camera.
And below the cropped version with a few minor touches on Lightroom:
Visit our Phases of the Moon post to learn more about our natural satellite. You can also check out all our pictures of the moon on our Lunar astrophotography post!
Rokinon 135mm f/2 Accessories
Astronetics
The Astronetics mount is a 3D-printed system that attaches around the Rokinon/Samyang 135mm lens and acts just like telescope rings. You can mount a guide scope, the ASIAir, and the ZWO electronic auto-focuser to the Astronetics, and attach the entire thing to any motorized mount.
This is a smart, affordable, and easy way to use this lens just like a telescope and image all night with a computer or a phone/tablet with the ASIAir attached. The design makes it all fit in a compact way and we have been using this hardware whenever we take our lens out under the stars.
Astronomy Camera Adapter
We started using this lens with our DSLR camera, which gave us great results as you can see on our Rho Ophiuchi image. After about a year, we decided that we wanted to use a cooled camera with the lens instead so that we could get the best possible results, especially on hot Summer nights.
For this, we bought the ZWO DSLR adapter with filter holder. This allows us to easily attach our Rokinon 135mm lens to our ZWO ASI2600MC camera, and even add a filter whenever we need to.
We are glad to say that the adapter works really well and did not introduce any tilt or back-focus issues.
Our first picture with this setup was of the Christmas Tree and Rosette Nebula, which you can see if you scroll down a little further in this post.
Bahtinov Mask
To achieve the best possible focus with this lens without struggling, get yourself a small Bahtinov mask! We own a Bahtinov mask with a diameter of 100mm which fits perfectly on the lens. Once placed, you then just need to aim at a bright star, turn the focus ring manually until the spikes are centered, and remove the mask!
This is of course not needed if you already own the Astronetics with the ZWO EAF attached.
Star Shapes at f/2
What makes the Rokinon 135mm lens so good for astrophotography is that it can be used wide open at f/2, without showing distortions on your corners. Most affordable lenses, when used for astrophotography, need to be stepped down to around f/4 for the stars to look round all over your frame. This means sacrificing speed and, when going from f/2 to f/4, means you'd have to spend double the time on your target to gather the same data you would have gotten at f/2.
We've used this lens with several cameras, and have always been surprised by how nice the stars looked in the corners. The screenshot below is a terrible example, but we thought it would be fun to include it. It was taken from our Christmas Tree and Rosette Nebula image, and shows that the stars in our corners seem elongated... At first, we thought the lens was the culprit, but after running some tests, we realized that it was due to the ASI2600MC's sensor being slightly tilted!
With a different camera, we did not see this issue and so understood that the lens was doing its job perfectly fine at f/2.
Full Frame corners at f/2
When it comes to bad star shapes in the edges of your frame, the problem is much, much more obvious if using a full-frame camera. So how does this lens perform with a full-frame sensor?
We used this lens on a full-frame mirrorless camera when we imaged Rho Ophiuchi, and the stars were round all over the field! The screenshot below shows the upper left corner of the image, and as you can see, the stars look good all the way to edge of the frame.
So whether you own a cropped sensor or full-frame camera, you can expect this lens to show pinpoint stars all over your field of view even when shooting wide open at f/2.
Imaging Winter Nebulae with the Rokinon 135mm f/2 lens
The Rokinon 135mm f/2 lens has the perfect focal length for capturing large nebulae that would otherwise be cut off in most telescopes' fields of view. Later in this post we will give you several ideas for which targets to shoot.
Another great thing you can do is to include several deep sky objects in your frame, without having to bother with making a mosaic.
We framed both the popular Rosette Nebula and the Christmas Tree cluster in our frame and captured the two together.
The main thing you need to worry about is the angle, so that both objects fit just right without being cropped out by the edges. It is very interesting to see all this gas between the two bright nebulae, and how they seem to interact in some ways.
This was shot at f/2 wide open, and no cropping was applied!
GEAR USED:
Camera: ZWO ASI 2600MC
Lens: Samyang 135mm f/2
Mount: ZWO AM5
Power: Jackery Lithium Battery
Accessories: Astronetics
Processing: Pixinsight
ACQUISITION DETAILS:
Total Exposure Time: 15 hours
Exposure Time per frame: 6 minutes
Gain: 100
A Great Lens for Small Constellations
Not sure about you, but we also like to take pictures of constellations!
At 135mm of focal length, the Rokinon 135mm f/2 lens is a good fit for most small-size constellations. You can also get larger ones, like Cassiopeia, if paired with a full-frame camera!
The image below was shot with this lens and Canon Ra and as you can see, it fits perfectly in the full-frame field of view.
GEAR USED:
Camera: Canon Ra
Lens: Samyang 135mm f/2 mounted on Astronetics
Mount: Sky-Watcher EQ6-R Pro
Processing: Pixinsight
ACQUISITION DETAILS:
Total Exposure Time: 3 hours
Exposure Time per frame: 3 minutes
ISO: 1600
Examples of other constellations that would fit well at 135mm are:
Canes Venatici
Corvus
Lyra
Triangulum
Best Targets to Photograph with the Rokinon 135mm lens
In this post, we showed you a molecular cloud complex (Rho Ophiuchi), nebulae (Christmas Tree and Rosette Nebula) as well as a constellation (Cassiopeia) taken at 135mm. What other targets do we recommend adding to your list if you own this lens? Below are a few examples.
Here are some ideas of targets you can shoot at 135mm, without the need for mosaics:
M45 (The Pleiades)
M31 (The Andromeda Galaxy)
M33 (The Triangulum Galaxy)
M42 (The Orion Nebula)
IC 434 (The Horsehead Nebula)
IC 2118 (The With Head Nebula)
IC 2177 (The Seagull Nebula)
Anywhere in Cygnus, especially around the Sadr Region
With that said, there are also some deep-sky objects that you should ignore if you only have this lens to do astrophotography.
These include any very small object that would be barely visible in your frame, like tiny galaxies or planetary nebulae. The list of small targets is huge, but some of the most popular objects that you should probably skip until you get a telescope are:
M57 (The Ring Nebula)
M64 (The Black Eye Galaxy)
M51 (The Whirlpool Galaxy)
M13 (The Hercules Cluster)
Rokinon 135mm f/2 - Final Thoughts
The Rokinon 135mm f/2 lens is one of the most popular medium-telephoto lenses for astrophotography. We absolutely love this lens and consider it as part of our telescopes when choosing to shoot a target. This is our go-to lens for very large nebulae, or when we want to try including several objects in the same wide field of view.
Some key points about the Rokinon/Samyang 135mm f/2 to summarize this review are:
It has a fast aperture of f/2 which is great for astrophotography
It has a focal length of 135mm, ideal for very large nebulae
It is one of the most popular DSLR lenses for astrophotography
It has an affordable price, making it perfect for beginner astrophotographers or someone on a budget. It can also be found used online for even cheaper
If you would like to purchase this lens, you can do so on Amazon.
Clear Skies,
Antoine & Dalia
Galactic Hunter
