IRIX 15mm f/2.4 BLACKSTONE £574/$675

A real night owl of a lens, the Blackstone even has fluorescent engraved markings

Designed in Switzerland and built in Korea, the Irix 15mm is available in Firefly and Blackstone options. Both are optically identical but the Blackstone has a magnesium alloy rather than plastic casing, four weather-seals instead of three, 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.

Although lacking autofocus, the Irix includes the necessary electronics to operate the focus confirmation lamp in the viewfinder, and to control the aperture from the camera body. You can therefore shoot in Program and Shutter Priority modes, as well as just Aperture Priority and Manual.

The lens has a separate petal-shaped hood and a large 95mm filter attachment thread at the front.

Performance

Image quality is excellent, with good sharpness across the whole image frame, minimal lateral and spherical aberrations, and wellcontrolled distortion. Vignetting isn’t too bad at f/2.4, but coma and astigmatism are pronounced giving a noticeable and irregular shape to stars and other dots of light. Both are much improved by narrowing the aperture by an f-stop.