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

Sharpness

Many would argue that if there is just one attribute in a lens to pay overt attention to, it would be sharpness and the maximum resolution the lens in question is capable of. This is especially true in our pixel-peeping, megapixel-counting, measureabating world of modern photography. As such, you have arrived at our most comprehensive (and thus longest) page in this entire review.

We wanted to see not only how the Pentax DA 18-135 fared against its little brother, but against Sigma's offering as well. And because they are all zooms, we ensured to examine the major points along the focal length ranges of each. Additionally, for each millimeter setting you'll find not only examinations at the center, but the extreme edge of the frame as well.

Speaking of millimeters, you might be interested to know that for every focal length we shot at, the camera was placed exactly 100x the focal length away from our chart. For example, at 18mm, the camera was set to 1,800mm, or 1.8m. At 55mm, 5.5 meters, and a painstakingly difficult pleasantly convenient lining up 13.5 meters away for the long end of the DA 18-135 WR.

The below "starcharts" are valuable tests because they force a lens, no matter how sharp or soft, to reach its tipping point. When by observed by themselves, they do not offer much information about a lens' ability to resolve fine detail. But when shot in a controlled manner alongside other lenses also shot in the same way, the results will speak for themselves. Reading the charts is easy - the earlier the image blurs, the softer the lens. As you would expect for the contrary, the closer to the center before the converging lines are indistinguishable, the sharper the lens and the higher a resolution it is capable of attaining.

To enhance the comparison process, all the images were purposefully underexposed in order to avoid premature blurring and preserve details that would be obscured by brighter highlights.

And finally, a small but important detail regarding our methodology. We naturally shot with the Pentax K-3 as it's the latest offering from Pentax (as of this review's publication) to wield the K-mount. But, the K-3 has such incredibly high resolution sans any anti-aliasing that moire is certainly bound to appear with the test chart that we are using. As such, in order to strike the perfect balance between moire suppression and maximum resolution attainable, we employed the K-3's Anti-Aliasing Filter Simulator (Strength: Low). The low strength AA simulator was applied across every iteration below for consistency.

Without further ado, the comparison tests at 17/18mm (the widest of each lens), 35mm, 55mm, 70mm, and 135mm.

Comparison One - Center Sharpness at 18mm or 17mm

For our first sharpness comparison test, we were at the minimum focal length of each lens, 18mm for the Pentax's and 17mm for the Sigma. The following settings were applied across all the sample images during this iteration:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 18mm or 17mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-55
DA 18-135 WR
Sigma 17-70 "C"

F2.8

N/A

N/A

F3.5

F4.0

F4.5

F5.6

F6.7

F8.0

F10

F13

Comparison Two - Edge Sharpness at 18mm or 17mm

No change from above:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 18mm or 17mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-55
DA 18-135 WR
Sigma 17-70 "C"

F2.8

N/A

N/A

F3.5

F4.0

F4.5

F5.6

F6.7

F8.0

F10

F13

Comparison Three - Center Sharpness at 35mm

The only change here is the focal length:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 35mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-55
DA 18-135 WR
Sigma 17-70 "C"

F3.5

N/A N/A

F4.0

N/A N/A

F4.5

F5.6

F6.7

F8.0

F10

F13

Comparison Four - Edge Sharpness at 35mm

Same as the other 35mm grouping:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 35mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-55
DA 18-135 WR
Sigma 17-70 "C"

F3.5

N/A N/A

F4.0

N/A N/A

F4.5

F5.6

F6.7

F8.0

F10

F13

Comparison Five - Center Sharpness at 55mm

The long end of the shortest zoom in this test, the following were in effect:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 55mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-55
DA 18-135 WR
Sigma 17-70 "C"

F4.0

N/A N/A

F4.5

N/A

F5.6

F6.7

F8.0

F10

F13

Comparison Six - Edge Sharpness at 55mm

And yet again:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 55mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-55
DA 18-135 WR
Sigma 17-70 "C"

F4.0

N/A N/A

F4.5

N/A

F5.6

F6.7

F8.0

F10

F13

Comparison Seven - Center Sharpness at 70mm

Now the the DA 18-55 has fallen out, the 18-135 and the 17-70 are left to duke it at the latter's terminus:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 70mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

As you can see, the below images are slightly smaller than the above series of crops, which were all 100%. To see the 100% crops of the images below, which applies to all the remaining comparisons in this section, click on any of them to open an enlargement.

DA 18-135 WR
Sigma 17-70 "C"

F4.0

N/A

F4.5

F5.6

F6.7

F8.0

F10

F13

Comparison Eight - Edge Sharpness at 70mm

Our final showing with the Sigma:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 70mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-135 WR
Sigma 17-70 "C"

F4.0

N/A

F4.5

F5.6

F6.7

F8.0

F10

F13

Comparisons Nine and Ten - Center & Edge Sharpness at 135mm

Only one left standing at this end:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 135mm
  • No Off-Camera Flash
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: Automatically adjusted to match Aperture Changes
  • ISO: 100
  • Distance to Test Chart: 100x Focal Length

DA 18-135 WR - Center
DA 18-135 WR - Edge

F5.6

F6.7

F8.0

F10

F13

Verdict

There's no doubt about it - not once in a single of the 162 samples above does the DA 18-55 kit lens prove superior to its bigger brother. This is what we had been hoping for expecting considering the increased cost of the lens. But, because it had almost three times the zoom range, we were afraid that such a design would result in compromises as is usually the case with such large zoom ranges. We are happy to report that as far as kit lenses go, you can expect no such degredations in quality when deciding between the two.

Now, things are a bit different compared to Sigma's third incarnation of the popular 17-70mm zoom. At the widest ends of either lens' focal length range, the Pentax wants to edge the Sigma in center sharpness, which was surprising considering how the Sigma is faster. With fast lenses, there is an inherent expectation that the faster lens will be sharper at similar apertures as compared to the slower lens because a lens optimizes after stopping down a bit, with the common knowledge being "the faster lens is sooner to optimize than the slower lens." We are pleased to report that in the center, the Sigma does not exceed the sharpness of its weather-sealed rival at its short end.

In absolute terms, it's important to note that the 17mm appears a bit sharper at 17mm versus the 18mm at 18mm, however because of the magnification decrease from 18 to 17mm and the resulting decrease in resolution that ensues from such shrinking, the difference is negligible and thus seems to favor the Pentax.

Move to the edge and we were unable to discern a winner between the two in terms of sharpness, however the Sigma has the edge in contrast and certain in chromatic aberration control. The Pentax seems to have a tendency to allow purple fringing to show itself, a trend we see across all focal lengths unfortunately. Thankfully, in our real-world shooting, we were unable to find significant amounts of fringing. And once again we feel compelled to remind you that these are all 100% crops of a 24 megapixel image - good look spotting those minute amounts of fringing in images sized for the web or better yet, when easily removed in post processing software.

The above assessments match for rest of the focal lengths available on the 17-70 - there is but a splitting-hairs'-difference between the two. There is but one caveat, though, and one we were pretty blown away by. The Sigma maintains an astonishingly high level of resolution, clarity, and contrast in its edge at 55mm and 70mm.

For the final focal length, the 18-135's longest end was a bit underwhelming, never really matching the center resolution of its shorter focal lengths, and with the edges being even more disappointing.

Now that this behemoth of an assessment is behind us, we have to remind ourselves to take a step back and once again see the forest for the trees. Apart from faster maximum aperture and marginally-wider field of view, so far the corner and edge resolution looks like the sole measurable advantage one would gain by skipping the Pentax 18-135mm in lieu of the Sigma 17-70mm.

Don't worry though - on the very next page is our bokeh comparison involving all three lenses again, which should help us assess such a bold claim.


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