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

Bokeh

For our next assessment of the DA 18-135 WR, we look at the one quality that you can't objectively quantify. Japanese for "blur," bokeh in a photographic context has come to be defined as the out of focus portions (you know, the blurry parts) of an image. When aiming for shallow depth of field to isolate the subject in focus, the quality of the out of focus background can surely make or break an image.

In order to effectively assess the bokeh of the lens in question, we ran it through a few of its different focal lengths, matched by the DA 18-55 and Sigma 17-70 "C" for comparison as well. We started at 55mm because anything wider was very difficult to induce consistent bokeh without being very close to your subject with a distant background.

A note on the choice of focal lengths - it's important to note that the DA 18-135 WR isn't designed as (or even pretending to be) a fast wide angle or even normal lens that would allow for intentionally shallow depth of field at wider focal lengths. For this parlor trick Sigma's latest K-mount lens, the 18-35mm F1.8 "Art," comes to mind. Pentax's weather sealed superzoom, however, is certainly competent with a near subject in front of a blurry backdrop such as a portrait. Because of this, we chose to make our first comparison at 55mm.

Finally, our bokeh tests will consist of our pine cone model in front of a very busy background - branches, tree bark, leaves, etc. It's very challenging for a lens to render in a smooth blur. While the wall of Christmas light bokeh was a huge hit in our HD 55-300 WR review and we would prefer to use that, sadly that won't be revisited for this review because it's, well, summer. And when it's summer time, we don't prepare for visits from Santa like those people Down Under...

Comparison One - 18-55 vs 18-135 vs 17-70 @ 55mm

As it says in the heading, for our first focal bokeh comparison test, we were at the maximum focal length of the lesser kit lens, with the other lenses set to match. The following settings were applied across all the sample images during this iteration:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 55mm
  • Focus Distance: 1.5m
  • Distance between Subject and Tree to Right: 1.5m
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: automatically adjusted to match aperture
  • ISO: 400
  • Flash: None
  • Distance between Subject and Tree Behind it: 3m

For your analytical pleasure, we've included the entire aperture range from wide open (lens dependent) to F11, as the majority of your shots will be within that aperture range to mitigate diffraction. Especially when attempting to achieve shallow depth of field.

Clicking on any of the below images will allow for an enlargement.

DA 18-55
DA 18-135 WR
Sigma 17-70 "C"
F4.0
N/A N/A
F4.5
N/A
F5.0
N/A
F5.6
F6.3
F7.1
F8.0
F9.0
F10
F11

Comparison Two - 18-135 vs 17-70 @ 70mm

Now we move to the maximum zoom of the Sigma, comparing at that focal length. No change in the shooting parameters from the above test:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 55mm
  • Focus Distance: 1.5m
  • Distance between Subject and Tree to Right: 1.5m
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: automatically adjusted to match aperture
  • ISO: 400
  • Flash: None
  • Distance between Subject and Tree Behind it: 3m

Clicking on any of the below images will allow for an enlargement.

DA 18-135 WR
Sigma 17-70 "C"
F4.0
N/A
F4.5
F5.0
F5.6
F6.3
F7.1
F8.0
F9.0
F10
F11

Comparisons Three and Four - 18-135 @ 135mm - Near and Far

For our final testing of the 18-135's bokeh, we have two different scenarios. On the left is with the camera in the exact same position as all the above tests - 1.5m away from our model. We realized though that not always are you going to be able to so close to your subject (be it a critter or your kids), so we took a few steps back for the column on the right. Here we are now 4m away from the pinecone to see how much of an effect the distance change between the lens and the subject has at 135mm. 

Once again, the below shooting parameters haven't changed (except for the subject distance at 1.5m and 4m, respectively):

  • Tripod
  • 2s Timer per shot
  • Focal Length: 55mm
  • Focus Distance: 1.5m (left) and 4m (right)
  • Distance between Subject and Tree to Right: 1.5m
  • Camera Mode: Av (Aperture Priority)
  • Shutter Speed: automatically adjusted to match aperture
  • ISO: 400
  • Flash: None
  • Distance between Subject and Tree Behind it: 3m

Clicking on any of the below images will allow for an enlargement.

DA 18-135 WR - Near (1.5m)
DA 18-135 WR - Far (4m)
F5.6
F6.3
F7.1
F8.0
F9.0
F10
F11

Verdict

The above images speak for themselves - the DA 18-135 WR is capable of producing beautifully creamy backgrounds, excellent for portraits and other images that require subject-background isolation. This is especially true when the lens is zoomed in and the subject is nearby. Because of the compression effect common with telephoto lenses and their long focal lengths, it is easy to completely isolate your subject from what's behind it.

As you step away from your subject, the ability to isolate it via shallow depth of field becomes more diffcult simply by nature of the relatively slow aperture of the lens. This would not be the case with a telephoto zoom with a much faster aperture across its entire zoom range, such as the DA* 50-135 F2.8.

When comparing the lens to the Sigma 17-70 "C," we honestly cannot distinguish between the two lenses' outputs in a blind test. Even in the highlights, the DA 18-135 WR does a stellar job rendering them as attractive orbs rather than with distinctive sides (hexagons, octagons, etc.) indicative of straight aperture blades.

The bottom line is simply this - the seven rounded blades on Pentax's weather resistant 7.5x zoom certainly do an outstanding job across both the focal length and aperture ranges.

Our last comparison test awaits - pseudo macro and whether the 18-135 or 17-70 can pull it off.


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