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Studio Tests - Sony DT 18-55mm F3.5-5.6 SAM lens

The announcement of the Alpha 230 / 330 / 380 series was accompanied by that of four new, inexpensive lenses, between them designed to cover a broad range of shooting situations, and all featuring Sony's latest 'Smooth Autofocus Motor'. These new optics are the DT 50mm F1.8 SAM 'portrait' lens, DT 30mm F2.8 macro, DT 55-200mm F4-5.6 telezoom, and the DT 18-55mm F3.5-5.6 SAM. The latter looks destined to become the standard kit lens for Sony's APS-C DSLRs from now on (replacing the ageing DT 18-70mm F3.5-5.6) so we've tested it to see how good it is.

The DT 18-55mm F3.5-5.6 SAM performs very well for a kit lens, challenging the Olympus Zuiko Digital 14-42mm F3.5-5.6 for the crown of best all-round performer in its class in our studio tests. It's undoubtably superior to the DT 18-70mm F3.5-5.6 lens it replaces, maintaining image quality across the frame to match the demands of modern high resolution sensors in a far more convincing fashion.

Sharpness Sharpness is high for this class of lens, and impressively consistent across the frame at all settings (a big improvement over the 18-70mm). Unusually the lens tends to be sharpest wide open and deteriorate on stopping down, perhaps hinting at a slight focus shift at smaller apertures. Overall though there's really very little to criticise here.
Chromatic Aberration Chromatic aberration is generally pretty well-controlled. The only concern is some fairly strong red/cyan fringing in the corners at wideangle, but there's nothing to worry about at longer focal lengths - again an advance over the old 18-70mm.
Falloff We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the centre. There's really nothing of note here, only a stop or so wide open at 18mm.
Distortion Distortion is the biggest flaw in an otherwise impressive showing - barrel distortion at wideange is strongly pronounced at 3.3%, practically matching our current record-holder (the Canon EF-S 18-200mm F3.5-5.6 IS). Zoom in, though, and distortion progressively disappears; at the telephoto end it's insignificant.

Macro Focus

The 18-55mm's decent performance in our studio tests does come at a slight cost in close-up performance. Maximum magnification is impressive at 0.4x, at a closest focus distance of 0.23m and with a working distance of about 0.1m from the front of the lens ot the subject.

Center sharpness is high even at F5.6, however in our flat-field chart tests the corners are rather soft, due at least in part to strong curvature of field. They progressively sharpen up on stopping down, but never match the centre. Most other 18-55mm kit lenses do a bit better in this regard (although the old 18-70mm was rather worse).

Macro - 60 x 40 mm coverage
Distortion: negligible
Corner softness: High
Focal length: 55mm (83 mm equiv)

Autofocus

The DT 18-55mm F3.5-5.6 SAM debuts Sony's new 'Smooth Autofocus Motor', which replaces the screw-drive coupling from the camera body with a small in-lens motor for autofocus. This works perfectly well - focus is generally fast, reasonably quiet, and accurate - and there's no obvious performance penalty compared to the screw-drive system of the old 18-70mm. The one slight irritation is that Sony users will now have to get used to two switches for changing focus modes (something Nikon shooters have had to put up with for a long time), and remember to always use the one on the lens to change to manual focus, as otherwise the focus motor and gearing can be damaged.

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