Specific image quality issues

As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests.

Softness wide open

All F1.4 lenses will show a degree of softness wide open, due simply to the additional aberrations introduced by all that extra glass being used to form the image. The smc DA* 55mm F1.4 SDM is much like any other fast prime in this regard, and for a portrait lens this is genuinely no bad thing (let's face it, Aunty Nellie is scarcely likely to be flattered by the perfect delineation of every blemish and wrinkle, no matter how much you bang on about 'bringing out character').

Normally at this stage of a review we'd resort to everyone's favorite photographic subject, the brick wall, but given this lens's intended use we've pushed the boat out a little (although admittedly not much) and gone for a simulated portrait shot instead. This allows us to compare the sharpness at the centre and towards the edge of the frame, across a range of apertures under controlled conditions.

Here we've shot our lovely model under controlled lighting, and taken crops from the points indicated in the frame. The eye is the focus point, and central in the frame; at the edge we have our beautiful feather arrangement (which should be familiar from our camera reviews as a good test for the rendition of fine low contrast detail).

From the crops below you can see that, in isolation, the F1.4 shot doesn't look bad at all, and while contrast is rather low you may well be perfectly happy to see this level of detail in your portrait shots of your nearest and dearest. But stop down and you can see the sharpness increasing progressively and significantly; by F2.8 the crops are showing much crisper definition of fine detail, with the edge continuing to improve visibly all the way to F5.6. Of course using smaller apertures also increases depth of field, which will result in backgrounds becoming more distracting; selecting the optimum aperture for portrait work therefore becomes a delicate balancing act between these competing factors.


Background Blur ('bokeh')

One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. This is especially important in a portrait lens like the 55mm F1.4, which is likely to be used frequently at large apertures for selective focus effects - in such shots it's highly desirable for the background not to draw the viewer's attention from the subject.

As luck would have it, the 55mm F1.4 generally produces attractive bokeh, fully commensurate with its intended role. At F1.4 it paints out-of-focus regions in a fashion that's often a little harsh and edgy, but stop down to around F2 - F2.8 and they tend to melt away into, well, the background.

Pentax K20D F1.4 (50% crop)
F2 (50% crop) F2.8 (50% crop)

The lens's main weakness tends to be when confronted by point highlights or bright, narrow lines - branches and the like - which are rendered in a rather hard-edged, distracting fashion, especially at F1.4. Stop down to F2 and, while things smooth over a bit, they're still far from perfect. So you still need to keep an eye on your backgrounds and be selective, rather than just assume that your F1.4 lens can simply blur anything away into oblivion. Overall though, it seems fair to say that the smc DA* 55mm F1.4 SDM will give you much nicer bokeh than the older smc FA 50mm F1.4.

F2, Pentax K20D 50% crop

Chromatic aberration

Lateral chromatic aberration is negligible in our studio tests, and is equally near-impossible to find in real-world shots; quite simply it's not an issue when using this lens. However intense green/magenta bokeh chromatic aberration can be visible at wider apertures, with objects in front of the plane of focus surrounded by a magenta 'halo', and those behind fringed with green. As usual this effect diminishes on stopping down, and essentially disappear by F4. Also, once again, it's important to point out that the 55mm F1.4 is a huge improvement over its predecessor here.

F1.4, Pentax K-7 100% crop
F1.4, Pentax K20D 50% crop


The Pentax 55mm F1.4 is (like many other fast lenses) somewhat susceptible to flare when pointed directly at bright light sources, but with its relatively narrow angle of view this isn't necessarily a huge problem. It's something you may well have to worry about if you've somehow fallen into the habit of taking backlit portraits directly into the sun, but it's not really likely to be a common concern in normal use.

For the record, the flare patterns seen at various apertures with the sun placed in the corner of the frame are shown below; as usual these get gradually more defined on stopping down, and are positively objectionable at F22. Move the sun slightly out of the frame and you're likely to catch some residual veiling flare, but most of the image is unaffected. Note that we were only able to get these effects by specifically looking for them (which shows in the lack of any artistic quality to these samples); for the majority of the time, the recessed front element and deep hood mean that flare isn't a problem at all.

F2.8, Pentax K20D F8, Pentax K20D
F16, Pentax K20D F2.8, Pentax K20D (sun just out of frame)