Irix 15mm f/2.4 Blackstone

£559/$549 This night owl even has fluorescent markings

Designed in Switzerland and built in Korea, the Irix 15mm is available in Firefly and Blackstone options. They’re optically identical but the Blackstone has a magnesium alloy casing, four weather-seals, and fluorescent engraved markings for easy reading under very dull lighting.

As a manual-focus lens, the focus ring has a typically smooth and precise operation with long rotational travel. It comes complete with a focus distance scale that includes markers for depth of field and hyperfocal distance at various apertures.

A secondary ring enables you to lock the focus ring at any position. Another nice touch is that you can fine-tune the focus ring so that the distance scale is calibrated to your camera body.

Performance

Image quality is excellent, with minimal lateral and spherical aberrations, and well-controlled distortion. Vignetting isn’t too bad at f/2.4, but coma and astigmatism are pronounced, giving a noticeable and irregular shape to stars. Both factors are much improved by narrowing the aperture by an f-stop.

N-photo verdict

Coma and astigmatism at the widest aperture make this good lens less appealing for astrophotography.

Sharpness

Sharpness is excellent across most of the frame, even when shooting at the widest aperture.

Fringing

Spherical and lateral chromatic aberrations are minimal, but coma and astigmatism can be severe.

Distortion

The Irix does very well to minimize barrel distortion, giving one of the best lab results in this group.