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

Vignetting

In this assessment of the lens, we focused on the amount of vignetting produced by the lens, or the characteristic where the brightness of an image is not uniform across the entire frame, particularly the further one gets toward the edges of the frame.

Before we get to the images, it's important to note that the complete removal of any and all vignetting from a lens' widest apertures, if not entirely impossible, would require an extremely complex with very large optical elements (and thus big dollars). Even for the most expensive lenses available to consumers, across any brand, vignetting is expected.

Minimum Focal Length (18mm)

For our first focal length test, we were at the minimum focal length of the 18-135 WR. The following settings were applied across all the sample images during this iteration:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 18mm
  • Off-Camera Flash w/ Umbrellas
  • Camera Mode: X-Sync (Flash)
  • Shutter Speed: 1/180s
  • ISO: 80
  • Flash Power Manually Adjusted to Match Aperture Changes
F3.5
F4.0
F4.5
F5.6
F8.0
F11

Medium Focal Length (55mm)

For our next focal length, 55mm and with a maximum aperture of F4.5 now, the following settings were in effect (same as above):

  • Tripod
  • 2s Timer per shot
  • Focal Length: 18mm
  • Off-Camera Flash w/ Umbrellas
  • Camera Mode: X-Sync (Flash)
  • Shutter Speed: 1/180s
  • ISO: 80
  • Flash Power Manually Adjusted to Match Aperture Changes
F4.5
F5.6
F8.0
F11

Maximum Focal Length (135mm)

Finally, we wanted to see how the DA 18-135 WR managed vignetting when zoomed all the way in. Other than starting at F5.6 because that is "wide open" at max tele, once again there was no change in the testing methodology:

  • Tripod
  • 2s Timer per shot
  • Focal Length: 18mm
  • Off-Camera Flash w/ Umbrellas
  • Camera Mode: X-Sync (Flash)
  • Shutter Speed: 1/180s
  • ISO: 80
  • Flash Power Manually Adjusted to Match Aperture Changes
F5.6
F8.0
F11

Verdict

As you can see, the DA 18-135 WR does not manage its corner darkening uniformly. So how will this affect your photography in the real-world?

At its widest apertures, predominantly used for landscapes and capturing wide swaths of buildings' interiors, the vignetting will be at its most detrimental. This is especially true considering the fact that the DA 18-135 doesn't seem to improve all that much despite stopping down 2-3 stops, the optimal apertures for maximum depth of field and sharpness. Correctable in post processing software such as Adobe Lightroom, the lack of change in the exposure difference across the frame isn't the end of the world, however at wider field of views the DA 18-135 WR leaves much to be desired in this regard.

Conversely, as you increase in focal length, approaching portrait territory--where vignetting would not be chastised--the lens does an excellent performance of maintaining an evenly lit frame. From medium telephoto all the way to its maximum zoom, vignetting incurred because of the DA 18-135 will have a negligible impact on your photographic output, especially upon closing the aperture one stop.

Click next for an examination of aberrations when shot in harsh sunlight.


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