Conclusion

The Irix 15mm f/2.4 is an excellent super-wide-angle prime lens that delivers very good image quality. Sharpness in the centre of the frame is excellent throughout the aperture range, even wide open at f/2.4, with f/4-f/11 producing the best results. The edges of the frame aren't quite as sharp, but still very good.

The Irix 15mm f/2.4 is a pleasure to use, thanks to its superb build quality, smooth focus ring and hyperfocal scale. As this is a manual-focus only lens, you'd expect this aspect of the operation to be intuitive, and so it proved. Together with the Canon EOS 5DS R's Manual Focus Assist feature in Live View mode and the confirmation beep when using the optical viewfinder, the Irix 15mm f/2.4 delivered a high percentage of keepers, despite the shallow depth of field when shooting wide open. The 25cm minimum focusing distance also makes the lens versatile enough to shoot close subjects.

There are a couple of minor drawbacks to the Irix 15mm f/2.4. Vignetting is obvious wide-open at f/2.4 and still fairly evident at f/5.6, although in real-world use it's less of a problem than when photographing a white wall/test-chart. Secondly, the 95mm front filter size is pretty expensive, although certainly better than no filter system at all, and you can alternatively choose to fit rear gelatin filters.

The full retail price of £399 / $400 for the standard Firefly version that we tested seems very reasonable for such a wide-angle lens, especially given the overall build and optical quality. If you want an even sturdier lens with useful engraved fluorescent markings and a better case, then the Irix 15mm f/2.4 Blackstone costs another £200 / $200, although as both lenses have the same optical and mechanical construction, we'd probably choose the cheaper option.

Ratings (out of 5)
Design	4.5
Features	5
Ease-of-use	4.5
Image quality	4.5
Value for money	5