Irix 15mm F2.4 Firefly & Blackstone Review

General Image Quality

On the following pages we will look in detail at every measurable performance parameter, but for the moment we will consider those subjective elements that can make or break an image.

Field of View

15mm falls straight in the ultra wide territory. This focal length delivers a field of view much wider than what the human eye is used to see. Creating a rectilinear lens (as opposed to fisheye) at this focal length is a challenging task. Using this focal length also comes with challenges, as composition will be influenced by light sources, tilted perspective and the like. Using Pentax's composition adjustment tool will come in handy in some cases, to keep lines straighter and more vertical.

15mm is a focal length well suited for landscapes and cityscapes, much less so for portraits where it can deform perspective and produce unflattering results.

Color and Contrast

When used properly, the Irix 15mm can deliver beautifully saturated images. Subtle color gradations and a good balance between light and shadows yield a lot of fine detail, as can be seen in the square windows and triangular tympanum below.

The following example show the lens' good saturation output.

Metering and Exposure

We have found that, in many instances, the Irix 15mm tends to produce under-exposed images when used on a K-1. A correction of 0.7 to 1 EV usually improved things greatly.

Starbursts

Starbursts are almost absent from images produced with the Irix 15mm at wider apertures. With its nine rounded aperture blades, this is not surprising. At F8 there is evidence of the effect, but the rays are diverging and not particularly pleasing. Considering the lens' tendency to create flare (see the relevant section) we do not advise to try to create starbursts, as the cost is likely to be higher than the benefits.

The images below show what can be expected at F2.8 and F8. Clicking on the images will bring up a crop.

F2.8
F8

Lens Corrections and EXIF Data

As with all third-party lenses, the Irix 15mm F2.4 does not benefit from in-camera corrections.

EXIF data is still complete and accurate, and Pentax camera bodies are able to record every relevant parameter into the file. Note that it is up to your software to properly decode this data when an image is viewed on a PC. The lens' version (Firefly or Blackstone) is of course not recorded, only the focal length.

On-Board Flash Usage

The K-1 does not have an on-board flash. When testing on a K-3 (an APS-C DSLR), the lens created a strong shadow, especially if the lens hood was in place.

Decentering

There have been many reports in our forums of decentering problems with the Irix 15mm. The company appears to stand behind its products and repair the faulty units, but this is still troublesome.

Our Blackstone test unit showed evidence of decentering, made apparent in particular during our vignetting tests, as can be seen on the image below.

We took care, during our tests, to limit the influence of this effect as much as possible.

User Report

The Irix 15mm is a fun lens to use. Well made, sturdy and with a good weight to it, it feels like a reliable tool. On the other hand, it is not a lens that one simply mounts on the camera and start shooting blindly. An ultra wide, manual focus lens comes with a learning curve.

Focusing can be tricky if one tries to adjust it as would be done with a more normal focal length. Shooting with the focus set at infinity will also not always work. Using the company's hyperfocal markings and selecting the aperture properly will work better. Irix understands this, and judiciously provides the focus lock which comes in handy.

No one selects 15mm for subject isolation. Using a medium to small aperture and a tripod is the best bet in most cases. When used at its best, the Irix produces pleasing and rewarding results.

In the next sections we will look at the optical performances of the Irix 15mm F2.4.