The Samyang 24mm f1.4 ED AS IF UMC is a wide-angle full-frame lens available for Nikon, Canon, Sony E-mount, and MFT DSLRs. Announced in January 2012, it’s the widest member of Samyang’s line-up of f1.4 full-frame primes comprising 24mm, 35mm, 50mm, and 85mm f1.4 models. Samyang lenses are also sold under the Rokinon and Walimex brand. Large aperture 24mm lenses are quite attractive additions to interchangeable lens bodies of APS-C/DX or FF/FX format: On the former bodies they are roughly equivalent in angle-of-view and depth-of-field to a 35mm f2.0 lens (on a full-frame body) which is quite attractive for reportage / street photography as it’s fast and gives some background isolation. On a full-frame body a 24/1.4 lens would be the widest f1.4 lens from Samyang that you can get, giving a clearly larger field-of-view than 35mm or 28mm lenses. It lets you capture more of architecture or landscapes plus lets you shoot longer under diminishing light and isolates closer subjects at least a bit from the background. Only Sigma offers a wider full-frame f1.4 lens: their Sigma AF 20/1.4 DG HSM “Art” (see my Sigma 20/1.4 Art review).
How does the Samyang hold out against its chief competitor, the Sigma 24/1.4 “Art”? To find out I compared the Samyang 24mm f1.4 ED on the demanding D810 body not only against the Sigma 24mm f1.4 Art, but also with Nikon’s own 24/1.4G ED and 24/1.8G ED. So if you’re shopping for a wide-angle lens, this review will give you some answers!
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Facts from the catalog
As usual I’ll have a look at the technical data first. I’ve rated the features with a [+] (or [++]), when it’s better than average or even state of the art, a  if it’s standard or just average, and [-] if there’s a disadvantage. I’ll compare it with the Sigma Art AF 24mm 1.4 DG HSM (the “Sigma 24/1.4” for short).
Size (diam. x length): 83 x 97mm (3.3 x 3.8in). This is the longest 24/1.4 lens but the Sigma 24/1.4 is only a little shorter at 85 x 90mm. 
Weight: 680g (24oz.). The Sigma 24/1.4 comes in at 665g. 
Optics: 13 elements in 12 groups. The cross-section shows four ED elements plus two aspherical elements. The Sigma 24/1.4 has 15 elements in 11 groups. [+]
Closest focus distance/max. magnification: 0.25m (0.82ft) / 1:5.3. This gives you a working distance of around 11 cm when you don’t use the lens hood. The Sigma 24/1.4 is the same.
Filter-thread: All 24/1.4 lenses use 77mm filters. That’s the size that most pro-lenses use. [+]
Image Stabilization: No 24mm prime lens offers optical stabilization except for Canon’s EF 24mm f2.8 IS USM. And with the small magnification at a focal length of 24mm it is no big loss. Still: shooting dim interiors or landscapes in fading light hand-held can prove quite a challenge without stabilization. 
Auto Focus: No, the lens is manual focus only. All the competition offers auto-focus. [-]
Covers full frame/FX or smaller. Same with the competition. [+]
Price: The Samyang costs around 550 EUR (incl. 19% VAT) which makes it the cheapest way to get a full-frame 24mm f1.4 lens. The Sigma 24/1.4 can be had for 750 EUR. [+]
Comes with a simple soft pouch. The lens hood is included, reversible for transport, and the lens-caps are similar to Nikon’s but the front cap is a bit slippery to pinch. The Sigma comes with a nicer well-padded case. 
Distance information is not relayed to the camera, the lens delivers a value of 3m regardless of the distance you choose. This disables some of the advanced exposure-related stuff e.g. a Nikon body can do although the lens does have electrical contacts and communicates some EXIF data with the body – at least in the Nikon version. The versions for Canon, Sony and MFT bodies have no contacts at all so cannot communicate anything to the body. The competing lenses from Sigma, Nikon and Canon relay subject-to-camera-distance and all the other EXIF information. 
Aperture ring: Yes, so you can control aperture directly from the lens. In the Nikon version you can also control the aperture from the camera by setting the ring to f22 but unfortunately there is no lock to prevent accidental movement. With the other versions of this lens you have no choice but to control the aperture from the ring. It clicks at half stops except between f1.4/f2.0 and between f16/f22. The respective lenses from Canon, Sigma, and Nikon don’t offer an aperture ring. [+] for Nikon version, [-] for all other versions.
Sealing: No. 
The score in the “features-department” depends on the version of this lens: For the Nikon version I tested it’s 1[-]/7/5[+], all other versions end up with 2[-]/7/4[+] because the aperture can solely be set at the lens. In direct comparison to the Sigma 24/1.4 Art the Samyang 24/1.4 ED has the one major disadvantage of offering no auto-focus, but it’s 200 EUR cheaper.
– The prime alternative is Sigma’s 24/1.4 Art that sells for around 750 EUR and performed very convincingly (see my Sigma 24/1.4 Art review) earning a Highly Recommended.
– For owners of Nikon DSLRs the gold-ringed AF-S Nikkor 24mm f1.4G from 2010 is the most expensive of Nikon’s current f1.4 lenses: 1700 EUR. See my Nikon 24/1.4G review where it earned a Highly Recommended.
– From Canon there’s the EF 24mm f1.4 L USM II selling for around 1300 EUR.
– If you can live with a maximum aperture of f1.8 or even f2.0 there are more alternatives: From Nikon there’s the new AF-S 24/1.8G lens (850 EUR) which earned a Recommended in my Nikon 24mm f1.8G ED review. And from Sigma there are two zooms: the 18-35mm f1.8 DC Art (680 EUR), which is a very interesting zoom but covers only DX sensors or the 24-35mm f2.0 DG Art (970 EUR, see my Sigma 24-35/2.0 Art review).
Focus and build quality
The lens is made in Korea and the general impression of build quality is solid but nothing in the class of the Sigma. The lens hood fits tightly and the focus ring has no slack/play between its movement and the focus-action. It has a throw of around 110 degrees, which is good for accurate focus wide open. The focus ring is 30mm wide and easy to grip and moves smoothly. But the lens has no weather sealing and its aperture blades produce only 8 diffraction spikes / rays whereas lenses with 7 or 9 aperture blades produce 14 resp. 18 spikes / rays.