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SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR Lens Review

John Riley reviews the SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC, a weather resistant, compact lens.

Posted: 26/05/2011 - 14:15


SMC Pentax-DA 18-135mm f3.5-5.6 ED AL [IF] DC WR

Weather resistant, compact, sporting the new DC motor and all in a very compact package, this new Pentax lens is very appealing. Braving the English rain, we shall see if its performance lives up to its potential.

SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR: Features

An impressive feature set starts with the simplified weather resistant construction. This makes it difficult for water to gain ingress and shooting in the rain becomes a real possibility. The SP (Super Protect) coating also repels water, dirt and grease, further aiding bad weather use.

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.

SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR: Handling

This is a very chunky lens and, unusually for Pentax, the manual focusing ring is located near the camera body rather than near the front. This means adopting a slightly different hold, but this is not a problem and just takes a moment to adjust to. The grip on both manual focusing ring and zoom ring is positive and the action of both is smooth but firm. The lens seems to be very well made and the finish throughout is to a high standard.

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.

SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR: Performance

So does the performance live up to the handling? As we look at both the lab tests and the in field photography, the answer to that is not as straightforward as we might expect.

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.

How to read our CA charts

Chromatic aberration (CA) is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.

Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.

For this review, the lens was tested on a Pentax K-5 using Imatest.

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.

How to read our MTF charts

The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges.

The scale on the left side is an indication of actual image resolution and sharpness as LW/PH and is described in detail above. The taller the column, the better the lens performance.

For this review, the lens was tested on a Pentax K-5 using Imatest.

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.

SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR: Verdict

There is a lot to like about this lens and in a practical sense it gives a good account of itself. There are design compromises that have lead to drawbacks, but often it is a matter of matching a lens design with the desired application.

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.

SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR Pros

  • Superb handling
  • Weather resistance
  • Silent DC motor
  • Close focusing
  • Quick Shift manual focus
  • Visually appealing images
  • High distortion levels
  • High CA levels

SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR Cons

  • High distortion levels
  • High CA levels
  • Low fine resolution at longer focal lengths
  • High price

Features: 4.5/5
Handling: 5/5
Performance: 3.5/5
Value: 3.5/5
Overall Verdict: 4/5

Pentax smc DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR Specifications

Manufacturer Pentax
Lens Mounts Pentax K SMC-FA
Focal Length 18mm - 135mm
Angle of View 11.9 - 76
Max Aperture f/3.5 - f/5.6
Min Aperture f/22 - f/38
Filter Size 62mm
Stabilised No
35mm equivalent No Data
Internal focusing No Data
Maximum magnification No Data
Min Focus 40cm
Blades 7
Elements 13
Groups 11
Box Contents
Box Contents No Data
Weight 405g
Height 73mm

Members gallery photos using: smc PENTAX-DA 18-135mm F3.5-5.6 ED AL [IF] DC WR

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