HD Pentax-DA 40mm F2.8 Limited

Aberrations and Flare

On this page, we will examine how the DA 40mm Limited controls various types of aberrations and artifacts.

Flare

According to Ricoh, the new HD coating "Enables the reduction of flare and ghosting for the shooting of clear, high-contrast images even under backlighting and other adverse conditions." As Pentax shooters already know, the previous SMC coatings were as good as any in the industry, so the previous bar is set high.

In the field, the DA 40mm Limited did indeed flare when a strong light source was in the frame. In a typical stress test, with the sun placed in the corner of the frame, the DA 40mm Limited showed a fairly typical flare. The crops below show the veiling glare introduced in the center of the frame, showing a roughly 10% reduction in contrast versus the same scene without the sun.

The veiling glare was reduced, but not eliminated, by stopping down. Click the thumbnails below to see larger versions of the scene at F2.8 and F8.

F2.8	F8
K-5 IIs, 1/640s, f/2.8, ISO 200	K-5 IIs, 1/80s, f/8, ISO 200

Flare at various apertures. (Click for larger images.)

Or course, this kind of flare can be used to artistic effect for those so inclined. Given the small size of the DA 40mm Limited's front element, it is fairly easy to shield the lens from sharp light sources.

In our previous comparison of the HD to SMC versions of the Limited lenses, the HD version did show a small improvement over the already-excellent SMC coatings. 

Shape of Flare

One of the key differences between the SMC and HD versions of the lens is the shape of the aperture blades. The SMC Limited lenses produce sharp starburst shapes due to straight aperture blades, but the HD versions do not.

It isn't until about F8 that the aperture blades have enough of an edge to create any kind of starbust at all. Even at F11, the shape of the flare isn't as geometric as the SMC version. The image below shows a typical shape of the flare in the HD version, taken at F11.

Typical flare in the HD version of the DA 40mm Limited. (Click to enlarge.)
K-5 IIs, 1/1000s, f/11, ISO 200

Chromatic Aberration

The DA 40mm Limited's weakness is a tendency for axial color (as discussed in the bokeh section) and for some purple fringing/'sensor blooming', mainly wide open. Stopping down to F4 improves both conditions.

The images below show a crop of a typical scene which provokes blue or magenta fringing. The crop at F4 shows an elimination of the aberrations. The whole scene is below (click for larger image).

K-5 IIs, 1.3s, f/4, ISO 200

Fixing Chromatic Aberrations

Typical chromatic aberrations, both axial color and fringing, can be treated with software such as Lightroom. For many images, a small amount of correction works immediately, as is clearly seen in the crops below from the New York skyline at F2.8.

Note that the above fix was a simple slider adjustment, with no fine tuning whatsoever.

While after-the-fact software can fix chromatic aberration, it can sometimes remove color which is part of the photo. In those cases, it requires more effort to fix. Luckily, stopping down resolves the issue as well.

Note that the in-camera CA correction using the K-5 IIs did not have a noticeable impact on the images taken with the DA 40mm Limited.

Verdict

The DA 40mm Limited isn't completely free of flare or chromatic aberrations, as the HD coating marketing may suggest. Instead, it is a small improvement over the SMC predecessor, which was industry-leading already.

Most of the DA 40mm Limited's aberrations are completely corrected by F4, an impressive result.

Those looking for geometric starbursts will bemoan the the rounded aperture blades compared to the SMC version.