Conclusion

The Irix 11mm f/4 is an excellent ultra-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/4, as are the edges, with f/5.6-f/11 producing the best results.

The Irix 11mm f/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 11mm f/4 delivered a high percentage of keepers. The 28cm minimum focusing distance also makes the lens versatile enough to shoot close subjects.

There are some minor drawbacks to the Irix 11mm f/4, and one major one. Vignetting is obvious wide-open at f/4 and still fairly evident at f/8, although in real-world use it's less of a problem than when photographing a white wall/test-chart. Secondly, the built-in lens hood prohibits the use of a front filter system, although the inclusion of a rear gelatin filter slot is some compensation. Our main concern is about the amount of chromatic aberrations that we found in quite a lot of our test shots, with very obvious purple and green fringing effects appearing in images taken on a sunny day with blue skies.

The full retail price of £549 / $575 for the standard Firefly version that we tested seems very reasonable for such a unique 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 11mm f/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
Value for money	5