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Lens review

Irix 15 mm f/2.4 Blackstone

27 September 2016
Szymon Starczewski

3. Build quality

The following chart allows you to compare the Irix 2.4/15 and its direct rivals. It is clear all those lenses can be divided into two groups. The Irix and the Milvus feature noticeably smaller front elements so it is possible to use classic filters with them; apart from that they don’t have a built-in hood. The front element of the Canon and both Samyangs, on the other hand, is huge and slightly sheltered by a hood permanently fixed to the lens.

In the photo below the tested lens is positioned between the Samyang 3.5/8 Fish-eye and the Sigma A 1.4/35.

Irix 15 mm f/2.4 Blackstone - Build quality

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The Irix 15 mm f/2.4 Blackstone starts with a metal mount surrounding a black, metal bottom with contacts and a 30×30 mm slot for gelatin filters. A rear element, 21 mm in diameter, is movable but its range is very narrow. The area around it is black, well-matted, without any slits which would enable dirt to invade the interior of the construction.

The presence of contacts means the aperture can be controlled via your camera menu. The problem is that you can’t set the f/2.4 value in Canon cameras – no matter whether you choose changing your aperture every 1/3 EV or 1/2 EV step, the maximum relative aperture displayed and saved in EXIF files remains f/2.5.

Irix 15 mm f/2.4 Blackstone - Build quality


A black, metal ring with slight ribbing in the middle is the first part of the proper lens body. There is a white dot on it, making an alignment with a camera easier, the name of the lens, information that it was designed in Switzerland and produced in Korea („Swiss Design, Made in Korea”), along a “neutrino coating” inscription. Above the ribbing you see a depth of field scale with marks at f/16, f/11 and f/8 and the infinity mark for infrared (R). Compared to the Samyang it is a step forward because the latter didn’t have any scale at all. Still if you stack it up against the manual Zeiss Milvus the Irix looks rather mediocre. The Milvus’s DOF scale is much wider and far more useful, including marks up to f/2.8. What’s more, even the Canon featuring autofocus can have marks up to f/5.6 so more than the completely manual Irix.

Irix 15 mm f/2.4 Blackstone - Build quality


A manual focus ring, as wide as 32 mm, is the next part of the lens. Most of its surface is covered by ribs under which you see a hyperfocal distance scale expressed in meters and feet and the range of hyperfocal distances by f/8, f/11 and f/16. The ring moves smoothly and is well damped; the resistance of its work can be additionally controlled by another unlock/lock ring. What’s more, the ring offers you the “infinity click” function: when setting the focus to infinity there’s an audible ‘click’ – a tactile feedback. Running through the whole distance scale needs a turn through an angle of 145 degrees. It is a range significantly narrower than that of the Samyang, amounting to 250 degrees; it explains the not exactly useful depth of field scale, described here earlier.

Irix 15 mm f/2.4 Blackstone - Build quality


Behind the focus lock ring you find a metal part of the casing which diameter swiftly increases; it turns smoothly into a petal-type hood mount.

Irix 15 mm f/2.4 Blackstone - Build quality


The front element of the lens is immobile and convex; it is also 47 mm in diameter - not a high value for a lens with such parameters. It is surrounded by a filter thread which doesn’t rotate and is 95 mm in diameter.

It’s worth noticing that the casing of the lens, made of aluminum and magnesium composites, features weather sealing against dust and moisture. There are four rubber gaskets inside the construction protecting the bayonet mount of the lens, the focusing mechanism and the front element as well, making the lens able to withstand extreme weather conditions. The engraved markings are covered by fluorescent pain which reacts to UV rays; it makes them glow in poor lighting conditions and more visible. We grant it: the meticulous, detail-oriented finishing of the lens really sticks out. No matter whether you just hold it or use it you have an impression of handling a solid, top-of-the-range piece of equipment.

Irix 15 mm f/2.4 Blackstone - Build quality


The optical construction of the Irix 15 mm f/2.4 consists of 15 elements positioned in 11 groups, with two aspherical elements, three made of HR (high refractive index) glass, and two made of ED (extra-low dispersion) glass. Both versions of the lens feature identical optical constructions. Inside you can also find an aperture with nine diaphragm blades which can be closed down to f/22.

Irix 15 mm f/2.4 Blackstone - Build quality


The rich accessory kit of the lens is really impressive. In the box you get a front cap, two rear caps, a petal-type hood with a window, a profiled and embossed hard case and a metal caddy for safe storage. Even lenses several times more expensive can feature much more modest accessory kits.

Irix 15 mm f/2.4 Blackstone - Build quality