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

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.

	CA	MTF20	MTF50
18mm
35mm
70mm
135mm

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.

Pleasing results from fill-in flash in fading daylight, ISO200, 1/125, f/4.5, 68mm (35mm equiv: 102mm)		Alison poses for a test shot in the studio, ISO100, 1/100, f/8, 135mm (35mm equiv: 202mm)
The widest shot at 18mm, ISO200, 1/125, f/8, 18mm (35mm equiv: 27mm)		The longest zoom at 135mm, ISO200, 1/160, f/8, 135mm (35mm equiv: 202mm)
The passageways of Manchester show moderate distortion with careful choice of viewpoint, ISO200, 1/30, f/8, 24mm (35mm equiv: 36mm)		Coarser detail is reproduced well, along with vibrant and attractive colour, ISO200, 1/200, f/8, 78mm (35mm equiv: 117mm)
A good level of detail is present in this shot in the rain, ISO200, 1/160, f/8, 21mm (35mm equiv: 31mm)		An ideal range of focal lengths to capture most events as they unfold, ISO200, 1/100, f/8, 21mm (35mm equiv: 31mm)

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