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I've been reading a lot about the Pentax DA 18-135mm lens and its performance compared to other lenses. I've heard that this lens is very soft at 135mm regardless of aperture. However, I've also read that the image quality is overall better than the 18-55mm lens. I am confused about the performance of the two lenses as a result. Since I own an 18-55mm lens (came with my Pentax K-r), how does the image quality of the 18-135mm lens compare to the 18-55mm, especially wide open in the edges and corners? Is it better or worse than the 18-55mm in terms of resolution?

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    \$\begingroup\$ The PhotoZone test of the 18-135 was abysmal. So bad that it seems like a bad sample, though Pentax said otherwise. photozone.de/pentax/597-pentax_18135_3556 \$\endgroup\$
    – coneslayer
    May 3, 2011 at 16:48
  • \$\begingroup\$ I can't help but think that the PhotoZone test was based on a bad unit, but I can't say for sure until there are more resolution tests for this lens. I'm still waiting for LensTip to test this lens. I wanted to make sure that it was no worse than my 18-55mm kit lens. That's why I asked this question. \$\endgroup\$
    – bwDraco
    May 3, 2011 at 16:59

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It's a pretty decent lens, despite what the Photozone review says. You've already seen the Pentax Forums review that includes crops of a chart. I'd trust your eyes over what some chart with numbers on the web says.

I've had the lens for a few months, and it's softer in the corners at the telephoto end compared to my DA* 50-135mm. Despite that, the 18-135mm lens is my most frequently used lens as it's "good enough" and it covers a very useful range.

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  • \$\begingroup\$ After reading the user reviews at Pentax Forums, I've come to the conclusion that the PhotoZone test was based on a bad unit, since the user reviews indicate that the lens actually performs very well at the 135mm end. Thanks! \$\endgroup\$
    – bwDraco
    May 3, 2011 at 17:50
  • \$\begingroup\$ I put very little stock in MTF charts these days simply because all lenses I've used have been "sharp enough", even the kit lenses that came with the K-5 (i.e. the 18-55 & 50-200). Put it this way, over the years there has never been a photo where I thought "If only I had a sharper lens, this photo would be better" whereas I've frequently slapped myself for not bringing a lens that was wide/long/fast enough. \$\endgroup\$
    – CadentOrange
    May 3, 2011 at 19:25
  • \$\begingroup\$ It depends where you start. Never tried the 18-135mm but when I had to send my DA* 16-50mm for repairs, my first idea was to get the 18-55mm as a cheap backup. Big mistake, the quality is horrible, everything looks like it was shot in a dark tunnel. I deleted all the photos from it, returned it and bought another 16-50m. After that I felt silly ruining good photos just to save $800. The lesson is to be careful with expensive gear, it is impossible to go back after! \$\endgroup\$
    – Itai
    May 3, 2011 at 20:28
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    \$\begingroup\$ It sounds like your 18-55mm lens was broken. \$\endgroup\$
    – CadentOrange
    May 3, 2011 at 21:07
  • \$\begingroup\$ Not really broken but similar to what I see with other kit-lenses. I'd say the Pentax is a little sharper than average but vignettes more and stopping down has little effect on that near wide-angle. Maybe I could have sent it for warranty service saying it vignettes too much. \$\endgroup\$
    – Itai
    May 4, 2011 at 17:05

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