Samyang 135mm F/2 ED UMC Review – Part 1

For those readers who are well versed in astrophotography, you might well have already come across this camera lens. Or, at least heard of its legendary status within the community. There’s few lenses that have the acceptance of being ‘the perfect astrophotography lens’, but this one is certainly 99.99% of the way there.

For those of you who haven’t heard of this lens, it’s a fully manual (manual focus & manual aperture) 135mm prime lens sold under the Samyang and Rokinon labels. With a focal ratio of F/2 at its widest aperture stop, going all the way down to F/22 at its narrowest, it’s an astrophotographers dream!

If you’re after one of these lenses yourself, they are completely identical from either company; Rokinon is more common in America, while Samyang is seeming more available in Europe and the UK. They are usually found in the region of £400-500 ($550-680), but keep your eyes open for an absolute bargain. I managed to pick mine up from eBay for a price that I simply couldn’t refuse.


The Details

This lens features 11 lenses in 7 groups, with one ED (extra low dispersion) lens to help reduce chromatic aberrations. This type of lens is well known for being incorporated into the higher-end telescopes, such as the William Optics Zenithstar & Sky-Watcher Esprit ranges of refractors, making this an apochromatic camera lens. Perfect!

It is classed as a full frame camera lens, as it fully illuminates a 35mm sensor, giving an 18.8º angle-of-view (AoV). It’s also fully compatible with APS-C and Micro 4/3 sensors as well, giving an 11.7º AoV for a Canon DSLR, with a slightly wider 12.4º AoV for a Nikon, and ending up with a 9.5º AoV for the Micro 4/3 sensor.

Towards the rear of the lens, resides the 9 aperture blades that are operated from the manual aperture ring closest to the camera body. Watching these open and close is quite a sight, as they perfectly intertwine to form an almost perfect circle in the middle.

Aperture Ring and Focus Distance Markings

For those who are using other camera manufactures, you’ll be pleased to know it comes in a large range of bayonet fittings, including:

  • Canon EF
  • Nikon F
  • Pentax K
  • Sony A
  • Canon M
  • Fujifilm X
  • Samsung NX
  • Sony E
  • MFT

The lens comes in a fairly standard cardboard box, and includes a nice velvet lens bag to store it in. It will permanently live in my camera bag though, so not needed in my case, but always nice to have one to hand. It also comes with the standard front & rear lens caps, as well as a reversible lens hood, which makes storing the lens a breeze in any situation.

One thing I would like to note here though, is that the lens hood is quite loose fitting. It doesn’t lock into place like some of my other camera lenses, allowing it to be easily rotatable and knocked off during use, so bare that in mind. However, once it’s on a star tracker, just leave it well alone!


The Good

What makes this lens so special for astrophotography is its light gathering capability – it’s like a black hole is on the front of my camera! I was able to easily frame multiple targets using the live view on the back of my camera; including the Andromeda Galaxy, Pleiades & Hyades, and the Heart & Soul Nebula (with some test exposures and manually plate solving using Stellarium on my phone) from my back garden in a Bortle 7 zone with no light pollution filter! Just incredible!

To go along with that low-light capability, it also has no coma from what I can see on my APS-C sensor. It’s also quite resistant to flaring from bright light sources, including the sun on a bright day – but please don’t look directly at it without the appropriate solar filter!!!

Initial impressions when handling the lens is very high quality indeed, with it being a substantial weight in the hand. The build quality is very high, and doesn’t have that plasticky feel of other lenses in the same price range. It also incorporates a 77mm filter thread, allowing for traditional camera filters such as circular polarisers and neutral density filters to be fitted to the front of the lens. Alternatively, as it’s a full frame lens, EOS clip-in filter can also be used. This would allow a general light pollution filter such as the Optolong L-Pro, or a narrowband hydrogen-alpha filter to be fitted to the camera body, which is incredibly useful!

And it just keeps getting better – when the lens hood is fitted, it makes it very easy to stand the camera on top of an iPad screen and take good quality flat frames – a rarity for a camera lens.

The internal focusing mechanism is perfectly smooth, with quite some resistance, which I personally like. What is also useful for astrophotography, is that there is a hard stop at the infinity and minimum focus points either side of the focuser ring. As the night sky is effectively an infinite distance away, all that’s needed is to set the focuser to the infinity mark and in theory, the stars are nice and sharp…however unfortunately that isn’t always the case.

The Bad

As is well documented by people like Nico Carver on www.nebulaphotos.com, the infinity hard stop can sometimes be just short of true infinity. This causes the stars to not quite be in perfect focus, and appear bloated. It’s only very subtle, but it is noticeable when using a Bahtinov Mask on a bright star and zooming in on the back of the DLSR – the central line isn’t quite central! After my first light image (stay tuned for the next post for this), I decided to fix this slight issue by taking the lens under under the knife…well, screwdriver.

Following Nico’s fantastic YouTube video, I disassembled the focuser collar, and revealed the hard stop that was causing the issue. However, I didn’t completely remove it as he suggested in his video, I simply moved the hard stop over as far to the right hand side as was possible, as shown below.

Doing this slight surgery now allows the lens to focus that little bit further and actually past the point of infinity, thus allowing perfectly focused stars in my images. And because the focuser is quite resilient, there’s no likelihood of the focuser moving over the duration of an imaging session.

I would not suggest doing this with a brand new lens though, as it would most likely void the 1-year warranty that comes with it. However, if the lens is second-hand like mine, it’s most likely older than 12-months and therefore it is a quick and simple job to do to achieve pinpoint stars.

I’ve since tried it out, and for me personally, that little fix has given the lens that last 0.01% it required to be THE perfect lens for astrophotography. I was ecstatic with the results I was getting with it before, but I’m so looking forward to getting it fitted to a mount and do some tracked exposures!


As I mentioned previously, this is part one of two posts on this lens. Please stay tuned in the coming days for the accompanying part, where I give this lens its first-light on my full-spectrum Canon 600D at the WolvAS Observatory.

So till then, I wish you all clear skies!

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