SMC Pentax-DA 17-70mm f/4 ED IF SDM Lens Review

SMC Pentax-DA 17-70mm f/4 ED IF SDM Performance

At 17mm central sharpness is very good at open aperture and peaks at f/5.6, just one stop down. After that sharpness slowly reduces, but is still very good at f/16 and good at f/22. The edges never really approach the central sharpness, being only fair throughout the range but peaking at a good level at f/11. CA is controlled tightly at the centre, being barely one quarter of a pixel wide at all apertures. An excellent result. The edges though show quite a bit of fringing, with high CA values exceeding 2 pixels width throughout. This edge CA can clearly be seen in images, but can of course be tackled in software. Distortion is an obvious -3.24% barrel, which again can be corrected in software.

At 35mm Central sharpness again starts off as very good, peaking one stop down at f/5.6 and remaining very good through to f/16. It remains good at f/22. Edge sharpness is poor at f/4 and f/5.6, rising to good levels by f/11 and f/16 before trailing off again to fair at f/22. CA however is much better than at 17mm, again excellent at the centre with exceptionally good figures. The edges are also much better, less than one pixel width. Pincushion distortion measures +1.18%, correctable but reasonably low in any case.

At 70mm, although the figures are slightly lower, the central sharpness is still very good from f/4 to f/16, peaking at f/5.6. It is still good at f/22. The edges fare less well, being poor at f/4 and f/5.6, fair at f/8 and good at f/11 and f/16. Sharpness falls to fair levels at f/16.

MTF 17mm
 

MTF 35mm
 

MTF 70mm
 

How to read our 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 as LW/PH. The taller the column, the better the lens performance. Simple.

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

CA remains very well controlled, especially at the centre of the field. Pincushion distortion measures +1.15%, another good result.

CA 17mm
 

CA 35mm
 

CA 70mm
 

How to read our charts

Chromatic aberration 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 minimise the problem, hence they usually cost more.

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

Bokeh is a bit fussy with this lens, not quite as smooth as lenses with more diaphragm blades. However, in general images were punchy and had a very good overall sharpness. The edges did let the lens down at longer focal lengths and wider apertures, although this could be taken advantage of with some subjects, perhaps close portraits.

Flare can be induced, despite the SMC coatings, and this is not helped by the lack of lens hood. Fortunately the hood is provided in the package with new lenses. Shielding the lens shows that given a hood or some other shield the resistance to flare becomes good. Into the light shots then retain contrast, saturation and sharpness very well.

Value For Money

There are now a few options in the Pentax range if we want to upgrade to a more interesting zoom than the standard kit lens. The SMC Pentax-DA 18-135mm f/3.5-5.6 ED AL IF DC WR lens (£379) extends the range at the cost of a slightly less wide view but also adds the faster DC motor and weather resistance. The HD Pentax-DA 16-85mm f/3.5-f/5.6 ED DC WR (£499) widens the view but only adds a small amount to the telephoto end, and also offers DC motor and WR construction. This compares to the £449 being asked for the reviewed lens.

Sigma also offers an alternative, the 17-70mm f/2.8-4 DC Macro HSM (£329) which gives that slightly wider maximum aperture at the widest end.

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