Pentax DA 18-135mm f/3.5-5.6ED AL (IF) DC WR
Review Date : Wed, 29 Jun 2011
Author : Jon Tarrant
Weather-resistant finish for use in all manner of conditions
|Cons:||Distortion at extreme focal lengths|
Pentax's 18-135mm zoom has a weather-resistant (WR) design - a claim to fame that only stands up if the optics are any good. Fortunately the optical performance is sound and there are also several other features that make this lens worthy of a second look...
Despite its compact size there is a full 7.5x zoom range that extends from a modest wideangle view to a potent telephoto. The zoom ring fills most of the lens barrel and offers just the right amount of resistance. To the rear there is a very narrow manual focus ring but it is clear, from both its size and its location, that Pentax expects this to be used only rarely.
In AF mode the focusing ring remains undisturbed thanks to a genuine internal-focusing mechanism. When manual focusing is needed it can be applied at any time, regardless of whether the camera is set to MF or AF (there is no mode switch on the lens itself). The motor is a direct current type that works smoothly and quietly but not particularly quickly.
It is obvious that Pentax is proud of its weatherproofed design because the seal on the rear of the lens is made of eye-catching orange rubber. Less obvious is the SP (Super Protect) coating that has been applied to the front of the lens and is claimed to help repel dirt, dust and grease. Inside there are both low-dispersion elements and aspheric profiles. Although chromatic aberrations are dampened they were visible in technical testing at both ends of the zoom range. There is some barrel distortion at short focal-length settings and pincushion distortion at the other end but careful placement of vertical lines will minimise the appearance of these effects in real-world pictures.
MTF (Modular Transfer Function)testing revealed very good results in the mid-zoom range and at the shortest focal length setting once the lens has been stopped-down slightly. The longest focal length produced the weakest results but even these figures are acceptable. Optimum performance is achieved at f/11, except at the 35mm setting where f/5.6 and f/8 dominate.
In use, the Pentax 18-135mm zoom is a straightforward and generally well-behaved lens. There are no switches to fuss over so full concentration can be devoted to the picture-taking process. The price tag is a shade on the high side for buyers who do not need a weather-resistant design but it can easily be justified on account of the supporting features, especially internal focusing and full-time manual intervention.
Overall, this is a capable, compact and comfortable-to-use lens that has the capability to overcome a range of different challenges, both photographic and meteorological.