Pentax-DA 18-135mm F3.5-5.6 Review
Construction and Handling
In this section we scrutinize every aspect of the physical construction of this lens so you can appreciate exactly what the mix of metal, plastic, and glass entails - before ever putting your sandwich clamps on one.
The only exception that won't be examined in this chapter is the "WR" epithet that is arguably the most exciting physical quality of the 18-135 WR. As such, we've dedicated an entire section to the weather sealing aspect on the following page.
The full official name of the lens is printed in a circular fashion, bordering the edge of the front element. Additionally, the size of the filter thread, in case you should ever forget, is also there to greet you upon inspection of the lens face.
Additionally, as mentioned previously on the Specifications page, the front element of the lens is coated with Pentax's Super Protect coating which promises a much easier to clean glass and that is also more reslient to dust, fingerprints, oils, and water drops. In practice we found the lens to be extremely easy to keep clean, with Pentax's claims of resiliency to be proven.
The DA 18-135 WR is a small, compact zoom with some distinct identifying features. For starters, the most eye-catching piece of flare is the vivid green ring that circumnavigates the widest portion of the lens barrel, a green that has come to signify Pentax's heralded smc lens coating.
The grip of the zoom and focus rings both share the same grid of waffle-esque bumps, rubber versions of the metallic rows of the mode dial on your K-7, K-5, and K-3 cameras.
At the base of the lens, between the metal mount and the start of the zoom ring, are two components. First, starting from the mount, is the beginning of the lens barrel emblazoned with the lens' name ( PENTAX | 18-135mm ) followed by the very narrow (about 5mm wide) focus ring.
The 18-135 WR features a robust focal range, from 18mm to 135mm. As such, and especially since it is not a premium grade zoom, it would be expected to have an external zooming system that causes the lens to extend and contract upon torquing the zoom ring. Additionally, to house such an extensive range, the DA 18-135 WR employs a telescoping design that features two inner barrels, as seen below:
The above image demonstrates both the minimum and maximum zoom positions of the lens. We also included a comparison of with and without the lens hood attached so you can see the effect the lens hood has on the overall size of the lens throughout its zoom range.
From the factory, the 18-135mm zooms with plenty of friction and without creep. Slight creep can develop over time, but it is very minor for a lens in this class.
The 18-135 WR is often regarded as an excellent "walkaround" zoom because not only is it weather resistant—a feature allowing it to be used despite Mother Nature's wrath—but it is also fairly compact. How compact? We placed it next to three lenses that also cover the "standard zoom" set of focal lengths.
As expected, the 18-55 is the smallest lens. Note that we didn't have access to the DA 18-55 WR for the conduct of this review, which does in fact come with a lens hood (same petal shape as the DA 18-135's hood, just a touch smaller). Because the DA-L 18-55 and the DA 18-55 WR share the same exact optical design, they are interchangeable for comparison purposes.
What's surprising is how similar in size the 18-135 is to its smaller "kit lens brother" despite the 80mm of extra focal length range and the same variable aperture range of F3.5-5.6. Also, while the lens bodies are for the most part the same size between the DA 18-135 and Sigma's latest 17-70mm offering, the front element is much larger on the latter, boasting a filter thread 10mm larger than the 18-135 WR's 62mm.
The DA 18-135 WR is equipped with internal focusing, the industry standard for modern high quality lenses. Internal focusing means simply that - the lens elements move back and forth within the lens housing to accommodate the range of focusing distances between infinity and its MFD (minimum focusing distance). This is as opposed to how older lens designs, whether a prime or zoom lens, extended or retreated their front elements as the focus ring was twisted (not to be confused with extension as a result of changing the focal length, aka "zooming").
For Pentax's lenses, you'll know if a lens features internal focusing by Pentax's [IF] trademark found in the official names of all their lenses.
For any sign of a focus distance scale, we regret to state that there is none. The lens designers have instead opted for the massive zoom ring that dominates the overwhelming majority of the lens barrel.
As to the actual performance of the focus system, we'll explore that in-depth later on in this review.
The below image shows the rear lens mount of the DA 18-135, which is obviously metal:
Some lenses come with a plastic mount (such as the aforementioned DA L 18-55mm kit lens). The mount combined with the 18-135 not being a tremendously heavy lens means that we have no worries of the mount eventually succumbing to old age and even hard use.
The below image shows the DA 18-135 WR with its lens hood attached, but facing either its front or its backside towards the camera. On the image below, focus on the lens hood on the right. Notice how the lens has a "window" of sorts with instructions to open it?
So by now you may be asking yourself, "What is that thing, and why would I open the side of a lens hood?"
The below image demonstrates exactly how this looks in practice when the hood is mounted, taken from the HD 55-300 WR In-Depth Review:
Have you ever attempted to rotate a circular polarizer filter while having a lens hood attached? While looking through the viewfinder to see the effect? Well, it's tough, thus requiring you to remove the lens hood, adjust the polarizer, and then re-attach the lens hood. A cumbersome (and annoying) process to say the least. And that's if you got the rotation correct and don't need to repeat the process. This window is the solution, allowing you to stick your finger through it from the bottom to rotate the CPL while the hood is still attached.
Ingeniously, Pentax has been offering this window in all their detachable plastic lens hoods. We would expect this out of something like the DA* line of premium lenses, but the fact that Pentax continues to bring this innovation to even the consumer line of lenses is nothing short of superlative. No one else in the camera industry has this standard, not even in their premium lenses, and we applaud Pentax for this touch. If this doesn't exude the impression, "For photographers, by photographers," we don't know what does.
For the last assessment of DA 18-135's external construction, here's an animated .gif showing the lens hood unattached and attached in its reversed/stowed away position. As you can see, it is extremely compact, adding a negligible amount of girth to the lens, thus making it a piece of kit never to be left out of the camera bag.
It's been mentioned that this is a variable aperture zoom lens. In order to make it easier to visually grasp the exact aperture range of this lens, namely where each maximum and minimum aperture lies along the entirety of the focal length range, we've created the following diagram for you. Above the axis lie the maximum apertures, with the minimum possible openings underneath.
In addition to the DA 18-135 WR and the DA 18-55, we included the latest incarnation of Sigma's 17-70 as well so you can see how its variable aperture range compares.
We were quite astonished to realize that with the 18-135, you lose only 1/3 of a stop for the majority of the zoom range, with the greatest variance being 2/3 stop between 28mm and 45mm. Compared to the much heavier and larger-front-element-wielding 17-70, we expected a larger difference between the two, especially considering how that with the 18-135 WR, you get not only weather sealing, but an additional 65mm of optical zoom.
On the next page we'll take a look at the 18-135mm's most exciting feature: the weather sealing.