Sony 18-70mm f/3.5-5.6 DT SAL-1870

Name: Sony 18-70mm f/3.5-5.6 DT SAL-1870
Brand: Sony
Rating: 6.0 (9 reviews)

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Lens Review
Specifications

18-70mm	$96 average price

Lab Test Results

Blur
Chromatic Aberration
Vignetting
Geometric Distortion

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Introduction
The 18-70mm ƒ/3.5-5.6 DT is the standard ''kit'' lens that ships with current Sony body / lens combinations. With an effective focal length in 35mm terms of 27mm to 105mm, the lens is versatile in wide-angle and light telephoto application. The lens is technically identical to its Konica-Minolta predecessor.

The 18-70mm ƒ/3.5-5.6 is a full-frame lens design, so it won't vignette on a Minolta film body or a full-frame Sony body. It weighs in at just over 8oz (235 grams) and takes the smaller 55mm filters. It ships with a solid circular lens hood and a carrying case, and is available for around $200.

Sharpness
The 18-70mm ƒ/3.5-5.6 offers above-average performance, never hitting a truly tack-sharp image, but not showing any noteworthy flaws, either. Corner softness is an issue in just about every focal length and aperture combination, but for the most part, you're looking at a difference of just 1-2 blur units, according to our blur test chart.

It's a hard one to call, but I would say the optimal point for this lens is at 50mm and ƒ/8. The image is quite sharp (1.5 blur units across the image) and at this setting you don't see the corner softness. The lens is actually quite well optimized at 18mm and ƒ/3.5, where many people will use it, quite sharp in the middle of the image and only slightly softer in the corners; this softness increases as you increase the focal length by zooming in.

Image sharpness degrades due to diffraction limiting as the aperture approaches the smaller end at ƒ/16 and above. As far as sharpness is concerned, there isn't a compelling reason to go above ƒ/16 - images are quite soft at this setting.

Chromatic Aberration
Chromatic aberration is quite evident at all focal length settings lower than 50mm, predominantly in the corners of the image. At smaller apertures chromatic aberration increases, so if you need to shoot wide, try and use a wider aperture to minimize this effect. At 50mm and above chromatic aberration is not noticeable except with some intense pixel-peeping.

Shading (''Vignetting'')
As is the case with most wide-angle zooms, there is some significant light fall-off in the corners when shooting wide-angle and wide-open (18mm, ƒ/3.5) - over a half-stop difference. Zooming in to 24mm decreases this to a quarter-stop, and at all other settings you're looking at less than that.

Distortion
No surprises with distortion here - as is typical for wide-angle lenses, set below 50mm there is significant barrel (''bloat'') distortion, seen at its most obvious at 18mm, where you're looking at almost a full 1% geometric distortion in the corners, and half a percent throughout the rest of the image. Happily this distortion decreases to near-zero as you approach 50mm, and pincushion distortion isn't a significant factor after that through to 70mm.

Autofocus Operation
The focusing operation of Sony 18-70mm ƒ/3.5-5.6 is conducted mechanically. The autofocus isn't particularly fast or quiet, talking probably around one second for the entire range. It's not an internal focusing lens, so there is some forwards-backwards travel as the lens focuses, but more importantly, the assembly rotates as it focuses, meaning any filters attached are also going to rotate as they focus. Not a huge issue, it just means that while using a polarizing or graduated filter you'll want to make sure you're focused before you align your filter to your preference.

Macro
The lens isn't a dedicated macro lens, but it focuses fairly close (1' 3'', 38cm) from the subject. The lens provides a magnification of 0.25x.

Build Quality and Handling
The lens is very well constructed, with a rugged plastic mechanism. Being a budget lens there aren't any frills such as a distance scale or aperture ring. The lens extends during zooming, almost half again its length. The focus ring travels about 1/4 of the diameter: not great for accurate manually focus, and the focus ring is almost an afterthought, with no real depth to grab on to. You can hear the gears whirring as you turn the focus manually. Being gear-coupled, manual focus can only happen when the camera is in MF mode.

Alternatives

Sony 16-80mm ƒ/3.5-4.5 DT Carl Zeiss ~$700
While a fair bit cheaper, this lens is a much higher quality lens than the 18-70mm, so you are getting what you pay for - somewhat sharper (though we detected significant issues with corner sharpness at certain settings) and a much higher build quality. The 16-80mm does have some issues with vigetting at wide angle (at 16mm, what lens doesn't) but distortion and resistance to chromatic aberration are better addressed.

Konica Minolta 18-70mm ƒ/3.5-5.6 D AF DT ~$90
This lens is technically the same as the Sony 18-70mm ƒ/3.5-5.6, but it was discontinued when Sony bought out Konica-Minolta. If you can find one used, it should give the same performance as the Sony but for a lot cheaper.

Sigma 17-70mm ƒ/2.8-4.5 DC Macro ~$350
A bit wider maximum aperture, slightly wider-angle and with the added perk of an integrated macro mode, for a few extra dollars you get a sharper lens with vastly better resistance to chromatic aberration, comparable distortion but a bit worse vignetting.

Conclusion
The Sony 18-70mm ƒ/3.5-5.6 is a capable kit lens, producing consistently above-average sharp images. It has some weak points - chromatic aberration below 50mm, and we're not big fans of lenses whose front filters turn while focusing or zooming. You shouldn't feel bad if you got this lens as part of the kit - you need to start with something, and while it's not the sharpest lens in the box it's not that bad, either. However, at these price points, if you're shopping for something in this range you might find a bit better performance for the money with the Sigma 17-70mm ƒ/2.8-4.5. Or, if you want to stay loyal to the Sony brand, invest a bit more in the Sony 16-80mm ƒ/3.5-4.5. Finally, if you're really stretched for cash and you can find one, the Konica-Minolta 18-70mm ƒ/3.5-5.6 is technically the same lens.

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.