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The KAF3 mount means that this lens has no AF drive shaft and therefore needs the newer generation of Pentax DSLR bodies, starting with the K10D providing that it has been updated to firmware v1.30 or above and with the K-5, K-r, K-7, K-x, K-m, K20D, K200D and K100D Super being fully compatible. Older bodies will mean using the lens for manual focus only.
The lens is constructed with 13 elements in 11 groups and the 7 blade diaphragm ensures a virtually round aperture for enhanced bokeh.
The new DC motor is silent and swift and the lens is also enabled for Quick Shift, a Pentax feature whereby after AF is achieved the focus point can be tweaked manually. This is especially useful in macro photography and, although not a macro lens, the maximum magnification approaches a useful 1:4.
The lens is quite chunky,taking 62mm filters, and weighs a solid 405g. The 35mm-equivalent range is 27.5-207mm. The metal bayonet is firmly secured by five screws, giving reassurance that the construction is solid and will wear well.
The lens balances well on the K-5 body that I tested it on and is a very useful range, ideal for a standard zoom. The Quick Shift feature is a real advantage in many situation especially, as mentioned above, close up shooting. The focus point can be fine-tuned after AF locks on without having to operate any additional switch. One nice thing about Pentax lenses is that there are no inconvenient macro settings to worry about – focusing is continuous throughout the range.
The new DC motor, built into the lens, is very slick. It is silent, fast and just locks on to the subject first time, every time. During this test there was not even one occasion when focus was not instantly achieved. Being used to the sound of conventional AF built into a camera body, this new style of focusing is quite odd at first, like living in a silent world.
The metal bayonet mount is smooth and locks firmly into place, more firmly than older lenses because of the weatherproof seal at the back of the lens. The Internal Focus means that the lens does not change length whilst focusing, although the focusing ring does still rotate.
In terms of handling and general functionality, this lens design would be very difficult to improve on.
In terms of photography in the field and in the studio, the lens performs very well. There's no doubt that images have superb colour, good sharpness and very pleasing bokeh. Aesthetically this scores very highly, producing very pleasant images.
The downside is in the compromises that have been made to make the lens as compact as it is and, probably, to make it Internal Focusing as well.
At 18mm, the lens puts in its strongest performance. The MTF50 chart shows good levels of detail, albeit it falling off in the corners. The MTF20 chart reveals a contrasty lens that has a high visual sharpness. This contributes to the good overall perception of the images. In terms of chromatic aberration, the centre of the field is very well controlled but this falls off dramatically towards the edges. It is in the area of distortion that things have been really let go, and we have quite high levels of barrel distortion that would easily be noticeable in architectural shots.
By 35mm the distortion and CA are coming under better control, and the high contrast is well maintained across the frame. The fine detail as shown by the MTF50 chart is not there in the corners, but is reasonable to about half way across the field. Images still look good because the coarser details are reproduced very well.
This pattern is maintained through the 70mm and 135mm charts. High central resolution falling over very severely towards the corners, good even contrast across the frame and good central control of CA being allowed to drift considerably toward the outer field and especially the corners. Distortion is quite visible throughout as it varies from wide angle barrel to telephoto pincushion.
However, we do not routinely buy lenses to take pictures of test charts and in the real world this is a very attractive lens that produces really good images. This is clearly because high visual sharpness is achieved through an excellent MTF20 result, where coarser detail is reproduced well across the frame.
If a lens for architecture and copying of documents is wanted, then this is not it. If it is wanted for general shooting of pictorial subjects and portraits then the lens produces excellent, visually appealing images that have a very attractive character about them. When we add to this the ability to keep shooting in the rain and cold, then we do have an extremely versatile option for Pentax users. In terms of handling the lens is an absolute joy to use.
|A versatile lens that produces pleasing results but with some optical compromises.|
SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR: ProsSuperb handling
Silent DC motor
Quick Shift manual focus
Visually appealing images
SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR: ConsHigh distortion levels
High CA levels
Low fine resolution at longer focal lengths
|VALUE FOR MONEY
|Construction||13 elements in 11 groups|
|Angle-of-view||79° ~ 11.9°|
|35mm equivalent focal length (on APS-C body)||27.5-207mm|
|Size (lxw)||73mm x 76mm|
|In the box||Front lens cap O-LC62
Rear lens cap
Lens hood PH-RBC 62mm