Irix 15mm f/2.4 Lens Review

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Pros
  • Excellent sharpness, especially centrally
  • No flare evident
  • Virtually no CA
  • Weather resistance
  • Filter use possible
  • Electronic control of aperture
  • Nice bokeh
  • Thoughtful, ergonomic design and features
Cons
  • Edges soft at wide apertures when close
  • Manual focus only

Irix 15mm F2,4 Blackstone Vertical View

The Irix 15mm f/2.4 lens is an ultra-wide rectilinear manual focus optic for full frame 35mm-format cameras, in this premium Blackstone version also being weather sealed and clad in magnesium alloy. Such a lens is a beautiful object in its own right, but the most important thing is the quality of the images it helps us to make. Let’s see if the results are the equal of the outward appearance.

Product Handling and Features

Irix 15mm F2,4 Blackstone On Canon 6D

The lens looks the part from the start, impressively mounted on the Canon EOS 6D used for this review. It matches the camera well and balances well. There is no AF, but there are electronic contacts on the mount so the correct aperture is reported in the EXIF data. The aperture, with its nine rounded blades, is controlled by the camera. There is a limitation in that the 6D cannot report an f/2.4 aperture value and instead reports f/2.5. This is a minor point of interest but has no real operational significance.

Mount options are listed as Canon EF, Nikon F and Pentax K, the Canon version weighing in at 685g and the Nikon at 653g. The weight of the Pentax version is not specified. The direction of focusing travel on the sample provided was correct for its Canon mount. Moving from the mount forwards, we find a depth of field scale, very useful when provided.

Next up is the wide manual focus ring, with clear markings in feet and meters. The paint used to fill the high-quality engraving is actually fluorescent, so in dimmer light, the markings stand of especially clearly. An excellent idea. The manual focus ring has more innovation to offer yet. There is a click stop at the infinity position, enabling that point to be found more easily when doing night shoots. There is also a guideline for setting the hyperfocal distance, with markings for f/16, f/11 and f/8. This is another excellent idea.

Forward of the focusing ring we have a focus lock. This enables a point of focus to be locked in and could well be useful when shooting a series of images at a specific distance. It will avoid any inadvertent focus shift. On the underside of the lens, there is also a recess for an adjustment to be made to the focus calibration to match the focusing scale of the lens with an individual camera, if found to be necessary.

Finally, the domed front element is protected by a very wide front rim that accepts not only the bayonet fit lens hood but also 95mm filters. It is very unusual for a lens with an 110-degree diagonal field of view to allow the fitting of filters, but it is possible with this lens. Thin filters will be best, and stacking of filters would almost certainly result in vignetting. If preferred, gelatin filters can be fitted to the rear mount of the lens.

Irix 15mm F2,4 Blackstone With Hood On Canon 6D

The bayonet lens hood deserves a special mention for the small cut out window that enables access to the rim of rotating filters, such as polarisers, to make their use possible when the hood is attached. This has been a hallmark of Pentax lenses for many years, but here the idea is improved as there is a sliding door to gain access rather than a removable panel that can easily be lost.

Lens construction for a 15mm lens has always been complex, even the first 1970s offerings having aspheric elements. This new lens takes that even further, with 15 elements in 11 groups of which we have 3 HR (High Refractive Index), 2 ED (Extra Low Dispersion) and 2 Aspheric elements.

This version reviewed is the Blackstone specification, which is a premium manufacture Aluminium-Magnesium alloy housing with weather sealing. It is beautifully made, with very high-quality finish. There is also a Firefly version available, with a more lightweight plastic construction and a lower price.

Manual focusing with such a wide angle lens can be tricky to judge but was found to be reasonable in practice. Any errors can be covered by the depth of field available, which is quite extensive. However, selective focus effects can be obtained where the main subject is very close to the lens. Arguably the best way to use a 15mm lens is to get in close and make use of the drama of the perspective that the close viewpoint gives. At first, until the feel for the lens becomes second nature, good advice would probably be to get in close and then go closer, which initially goes a little against the grain. The rewards are there to be had, with dramatic, sweeping perspectives.

Irix 15mm F2,4 Blackstone Rear Oblique View
Performance

So, does the technical quality of the lens match its quality feel?

Central sharpness is excellent from f/2.4 all the way through to f/16. It remains very good at f/22 and makes the inclusion of that very small aperture worthwhile. It means we can usefully take advantage of maximum depth of field when necessary.

The edge results are of course not as good at the close test target distances as they are out in the field. Field curvature makes the shooting of a flat test target more difficult for an ultra-wide lens to shine. As a result, f/2.4 and f/4 are relatively soft at the edges, f/5.6 improves to a good level, but it is not till f/8 that sharpness becomes very good. This becomes excellent by f/11 and remains very good at f/16 and f/22. In any event, this is a much better performance than 15mm lenses tried in the past.

IRIX 15MM F2 4 MTF

MTF

How to read our charts

The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges.

The scale on the left side is an indication of actual image resolution as LW/PH and is described in detail above. The taller the column, the better the lens performance.

Centrally, the CA figures are as close to zero as we could possibly expect, which is outstanding. At the edges, correction is remarkable for such an ultra-wide lens and any residual CA could be easily tackled in software. As it stands, this will probably not be necessary for most shots.

IRIX 15MM F2 4 CA

CA

How to read our charts

Chromatic aberration is the lens’ inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.

Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.

The flare resistance is just about complete and even when shooting right into the light there is no noticeable reduction in contrast. Images remain crisp and there are no spurious artefacts.

Distortion is well held at -2.07% barrelling, which is very reasonable for such a wide lens. Again, for most shots, I would just leave this as it is, although software correction is always possible if required.

The nine-bladed diaphragm, with rounded blades, gives a very pleasant appearance to the bokeh of the lens. It is easily possible to have out of focus areas in even a 15mm lens, especially where the main subject is very close. The gradation of the bokeh is smooth and satisfying to the eye.

So, to answer the opening question, yes, the Irix 15mm f/2.4 Blackstone lives up to its quality feel when the images are examined, and acquits itself very well indeed.

Irix 15mm f/2.4 Sample Photos

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