Pentax-DA 18-135mm F3.5-5.6 Review

Aberrations and Flare

Imperfections in an optical design can lead to chromatic aberrations such as fringing, lens flare, and ghosting, all unwarranted symptoms of having a strong light source enter your field of field.  When used in conjunction with a lens hood, modern glass coatings do an excellent job of suppressing lens flare, and some better than others. Pentax has been widely regarded as having some of the best coatings in the industry, a reputation built over decades through their "Super Multi Coating," largely known via the iconic smc.

As we mentioned earlier in this review, the DA 18-135 WR is the last lens to brandish the Pentax logo whilst also featuring smc initials. This is because Pentax has retired the three-letter title in favor of the proven-superior HD, or "High Definition," nano-crystal coating announced two years ago.

So does that mean the 18-135 WR should be considered obsolete in this regard? Let's find out.

Test One - Out-of-Frame Sunlit Angular Flare

For this comparison, extremely strong sunlight is used to backlight tree branches, a notoriously problematic situation for lenses to cope with. The lens was set to 58mm for this series, and the accompanying 100% crops are included, identified by the yellow box.

Entire Scene
100% Crop
F4.5
F5.6

Test Two - Inside-Frame Sunlit Angular Flare

For our next stress test, we didn't shy away from the sun, albeit with focusing assistance via LiveView to prevent lessen any temporary blindness. Additionally, the sun is positioned to the very extreme edge of the frame, particularly troublesome for wide angle lenses as the direct light source bounces across many optical elements. In turn, this often leaves behind a line of flare-induced orbs across the entire image. To stress the DA 18-135 WR in this regard, it was set to its widest focal length and an iris of F4.5 on the left and F11 on the right, respectively.

Click on either image below to open an enlargement.

We are unable to discern any critical differences between them regarding aberrations of any kind, at any point across the frame.

Test Three - Chromatic Aberrations at Maximum Zoom

Once again we kept the sun in the frame, only this type we were at the other extreme of the zoom range. On the left is wide open at F5.6 and on the right is F11.

Click on either image below to open an enlargement.

This time there's a very slight aberration in the form of yellow color cast below the sun and to the left. Other than that, there's no fringing of any kind in the pine needles, anywhere. Considering how strongly backlit they are, we consider this to be nothing short of remarkable.

Verdict

The DA 18-135 WR surely isn't missing out on much when it comes to mitigating forms of aberrations. There's some slight color casting near strong light sources, however it is far less than what we have seen with other lenses and what we were expecting to see in such harsh conditions.

As always, care should be taken when pointing your lenses in a direction that includes the sun, but otherwise we aren't too concerned about how Pentax's 7.5x weather resistant zoom mitigates flaring. We are especially happy to report this with regard to bright sunlight at wide angles.

In our Sample Photos page of this review, you'll notice a few images taken with strong light sources, and once again the DA 18-135 WR does a phenomenal job mitigating the negative effects of flare in all of them. One small caveat to be aware of it that for point sources such as street lights, flare is also well controlled. The inevitable "but" comes from the starbursts.

Because the resulting lines aren't razor thin until stopping down to F22 or smaller (which is unfortunate because of the ensuing resolution hit thanks to diffraction), some of the light bleeding might be attributed to poor flare control. An excellent example of this is the below image, shot by Pentax Forums member schnitzer79 (clicking on the image will open a larger version):

Pentax K-50, 18mm, 10s, F16, ISO 100

Note though that even these point sources don't result in heavy flaring.

Head on to the next page for our bokeh comparison between all three lenses.


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