Sony DT 18-70mm 1:3.5-5.6 Lens Review: 3. Test results: Digital Photography Review

Studio Tests

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NOTE the line marked 'Nyquist Frequency' indicates the maximum theoretical resolution of the camera body used for testing. Whenever the measured numbers exceed this value, this simply indicates that the lens out-resolves the sensor at this point - the calculated MTF values themselves become meaningless.

The Sony kit lens is a competent performer, overall about on a par with similar lenses from other manufacturers. Resolution is slightly low at the extremes of the focal length range; there are also issues with chromatic aberration from wideangle through to 35mm.

Resolution	Resolution is highest in the middle of the focal length range, falling away slightly at wideangle and telephoto. The lens also shows a distinct tendency towards softness in the corners at all focal lengths and apertures. Best results are (as usual) obtained around F8-11, before the onset of diffraction; and as always apertures of F22 or smaller are generally best avoided.
Chromatic Aberration	Chromatic aberration is a clear issue at wideangle settings, although no worse than other similar lenses; however it continues to be a problem further into the focal length range than usual (perhaps due to the extended overall range), with clear green/magenta fringing visible even at 35mm. CA also gets slightly worse on stopping down.
Falloff	We consider falloff to start becoming potentially problematic when the corner illumination falls to more than 1 stop below the centre. The 18-70mm is something of a star performer here, with just a little falloff even wide open at 18mm, which essentially disappears on stopping down even slightly. It's easily the best of the inexpensive kit lenses in this regard.
Distortion	Distortion characteristics are generally pretty good; there's the usual barrel distortion at wideangle, with a strong 'wave' character and corner re-correction making software correction relatively difficult. This slowly deminishes in magnitude through to near-neutrality at 35mm, beyond which we see mild pincushion distortion; in real-world terms distortion is likely to be imperceptible beyond 28mm.

Macro Focus

Coverage is a bit low by kit lens standards, with a magnification of 0.29x achieved at a minimum focus distance of 33.5cm, and a working distance of 19.5cm between lens and subject.

The image is reasonably good wide open and improves progressively on stopping down. There's also very little in the way of distortion or chromatic aberration, so overall not a bad showing at all.

Macro - 81x54 mm coverage
Distortion:Very mild pincushion
Corner softness: Low
Focal length: 70 mm (105mm equivalent)

Specific image quality issues

As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. Overall this lens is a competent performer, rarely throwing up any nasty surprises, but never hugely impressing either.

Chromatic Aberration

We're never surprised to see chromatic aberration on a kit lens at wide angle, but this lens unusually continues to show quite strong CA on zooming in to around 35mm. The visual effect of this is also effectively amplified on higher pixel count sensors, making it highly visible in the 100% crop from the Alpha 350 below (although no more likely to impact on an actual print).

35mm F8, Alpha 350	100% crop

Flare

The Sony 18-70mm shows admirable control of flare for a kit lens. With the sun placed in the top corner of the frame, it shows no discernible flare patterns, except for a slight loss of contrast towards the opposite corner. Even in strong side- or back-light, it rarely shows much more than a slight loss in contrast - impressive stuff.

16mm F8, sun in corner of frame	50mm F5.6, strong sidelight

Background blur ('bokeh')

One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. At 70mm F5.6, this lens can give substantially defocused backgrounds, but the blur pattern isn't particularly smooth (although no better or worse than other similar lenses).

170mm F5.6 Alpha 700	50% crop

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