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Studio Tests - E 18-55mm F3.5-5.6 OSS lens

The NEX-3 and NEX-5 will initially be available in kits with two lenses, the image-stabilized E 18-55mm F3.5-5.6 OSS and the E 16mm F2.8 'pancake', and for a start we're going to look at the zoom. We think this makes more much sense to buy as a kit with the camera if you're just getting one lens.

The E 18-55mm F3.5-5.6 puts in a pretty decent showing as APS-C kit lenses go, and easily holds its own against those typically bundled with SLRs. Sharpness is generally high (especially in the center of the frame), chromatic aberration is reasonably well-controlled and vignetting is very low; however this does come at the cost of pretty strong geometric distortion.

Sharpness results are a little mixed. At 18mm, sharpness is very high in the center but drops off progressively towards the corners. At longer focal lengths sharpness is impressively high and much more even across the frame. In general best results are gained around F8, much as we'd expect; stopping down to F22 or smaller will result in considerable degradation due to diffraction.
Chromatic Aberration
Chromatic aberration is reasonably well-controlled. As is normally the case there's visible fringing towards the corners at wideangle, which is mainly red/cyan in color. But this diminishes at longer focal lengths, and becomes nonexistent at the telephoto end.
We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the center. The 18-55mm effectively never shows any visible falloff at all.
Distortion is unusually high. At wideangle we measure 2.6% barrel distortion, which is complex in character with strong re-correction towards the corners (making it relatively difficult to correct in software when required). At longer focal lengths the distortion changes to the pincushion type, and reaches a whopping 2.4% at 35mm, which sets a new record for the strongest distortion of this type we've yet measured.

Macro Focus

Not a bad showing here, especially for an internal focus kit zoom. The measured minimum focus distance is 24cm, giving a working distance of about 14cm from the subject to the front of the lens, and a maximum magnification of 0.31x.

Image quality isn't great wide open, with noticeable softness across the frame, but stop down to F8 and the center sharpens up nicely, with the corners not far behind. There's a little pincushion distortion and a touch of lateral chromatic aberration, but nothing too objectionable.

Macro - 76 x 50 mm coverage
Distortion: slight pincushion
Corner softness: moderate
Focal length: 55mm (83 mm equiv)

Software correction of lens aberrations

One of the key elements of Panasonic and Olympus's Micro Four Thirds system is the integration of software correction of lens aberrations into the heart of the system. As usual we've looked in some detail into whether Sony might be following suit, and our conclusion is that no corrections for lateral chromatic aberration or geometric distortion are being used. It's possible some falloff correction is being applied, but if so it's prior to writing of the raw file.

Optical Image Stabilization

The E 18-55mm F3.5-5.6 OSS marks a first for Sony - it's the company's debut attempt at using optical image stabilization in an interchangeable lens. The Alpha DSLR line, of course, has always used in-body 'Super SteadyShot', but the drastic slimming that's been applied to the NEX's body means the stabilization unit simply won't fit. Sony has therefore incorporated 'Optical SteadyShot' into its kit zoom.

We've generally found the stabilization units in SLR lenses to be pretty effective in real-world use, and to quantify this, we subjected the 18-55mm to our studio image stabilization test at a focal length of 55mm, using the NEX-5 as the test camera. The subject distance for these tests was approximately 2m.

We take 10 shots at each shutter speed and visually rate them for sharpness. Shots considered 'sharp' have no visible blur at the pixel level, and are therefore suitable for viewing or printing at the largest sizes, whereas files with 'mild blur' are only slightly soft, and entirely usable for less critical applications.

55mm OSS OFF 55mm OSS ON

In-lens IS systems generally work very well, and Sony's is no exception. Under studio conditions it provides at least three stops of stabilization, and continues to give a decent chance of getting sharp shots at much slower shutter speeds. This is up there with the best in-lens systems currently available from the likes of Canon and Nikon.


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