Sony 18-55mm f/3.5-5.6 DT SAM SAL-1855

SLRgear Review
October 12, 2009
by Andrew Alexander

In May 2009 Sony elected to replace its 18-70mm ƒ/3.5-5.6 DT with a new 18-55mm ƒ/3.5-5.6 as a standard kit lens. While it doesn't have the 70mm reach, the 18-55mm lens features the SAM in-lens autofocus motor, for quick and quiet focusing.

The 18-55mm ƒ/3.5-5.6 DT was designed to fit only the APS-C sensor, and will show distinct vignetting if used on a Sony full-frame dSLR camera. Accordingly the lens produces an effective field of view of 27-83mm. The lens features a variable aperture, whose maximum size decreases as the focal length is extended:

A circular-shaped lens hood is available for the 18-55mm ƒ/3.5-5.6 DT, but is not included. The lens is available in a variety of camera kit combinations, or separately for approximately $200.

Sharpness
As a kit lens we aren't expecting amazing results for sharpness, that said, we were pleasantly surprised.

Wide open at 18mm and ƒ/3.5, the lens shows a generous area of sharpness reaching almost across the entire frame - around 1.5 blur units. There is some slight corner softness on the right side, and from one setting to the next this softness switches sides, leading us to assume our particular sample suffers from some de-centering. Stopping down to ƒ/4 shows negligible improvement, but at ƒ/5.6 and 18mm, the lens is very crisply sharp indeed, tack-sharp across the frame at 1 blur unit. It's sharp all the way to ƒ/11 at this setting, where diffraction limiting begins to set in, but even at ƒ/16 sharpness is only then beginning to reach 2 blur units.

In the mid-range of the zoom setting (24-35mm) we note some more extensive corner softness issues, prominently at 24mm and ƒ/4 where the left side reaches upwards of 5-6 blur units. That said, it's a small area of softness, mixed with a generous area of central sharpness (~1.5 blur units). Stopping down to ƒ/5.6 evens things out, and by ƒ/8 it's very close to tack sharp - just under 1.5 blur units, slightly sharper in the center. The lens is still fairly sharp at 55mm, at around 1.5 blur units on average, slightly softer at the corners. Stopping down to ƒ/8 or ƒ/11 offers only marginal improvement.

Fully-stopped down performance isn't great, but isn't as awful as we've seen on other lenses - best at 18mm, where we note just over 2 blur units across the frame at ƒ/22, and worst at 55mm where we note around 4 blur units at ƒ/36.

Chromatic Aberration
While a bit high at 18mm, chromatic aberration is on the whole quite well-tamed, especially at 28mm and longer. The results are fairly uniform from aperture to aperture, so there's no particular advantage to stopping down here.

Shading (''Vignetting'')
Corner shading is significant only at 18mm and 24mm; at other focal lengths, there is no appreciable light falloff. The corners are darkest at 18mm and ƒ/3.5, where we note corners that are 2/3 EV darker than the center. At 24mm and ƒ/4, the differential is just a bit lower than a half-stop. At any other setting than 18mm, corner shading falls below the quarter-stop differential; at 18mm, stopping down to ƒ/5.6 and greater will still show corners that are a third-of-a-stop darker than the center.

Distortion
Distortion results for this lens are nicely predictable: highly barrelled at wide-angle, and as the lens is zoomed out towards 55mm, distortion decreases until it is negligible at 55mm. Distortion is fairly high at 18mm (+1.0%) in the corners, and +0.5% throughout the rest of the image. If you want to keep your straight lines straight, shoot at 55mm.

Autofocus Operation
With Sony's SAM technology, the autofocus on the 18-55mm is quick and very quiet, focusing from infinity to closest-focus in about one second. Shorter focus changes happen quite quickly. It's worth noting that the front element does turn during autofocus operations, making life just that little bit more challenging for filter users.

Macro
Macro performance isn't bad for this lens, at 0.34x magnification. Minimum close-focusing distance is just 25 cm (just over nine inches).

Build Quality and Handling
The emphasis on this particular lens is on economy, with an all-plastic construction. The finish is nice to look at - a smooth semi-gloss black. Both the body mount and the 52mm filter threads are plastic, and accordingly the weight of the lens is quite low, only 210 grams (just over 7 ounces). There is only one switch, which enables or disables autofocus; there are no other perks such as a distance scale or depth-of-field scale, though the lens does feature curved diaphragm blades to improve bokeh appearance.

The zoom ring is the larger of the two, rubber with a raised ribbed texture, 5/8-inch wide. The ring takes about 35 degrees to turn through its zoom range, and the lens changes its length throughout; its shortest length is at 35mm, where the front element is basically flush to the body. At 18mm and 55mm, the front element is extended by about a half-inch. There's a good resistance on the zoom ring, making it easy to turn but not so easy that it would be subject to zoom creep.

The focusing ring will not win points with manual focus users. It is composed of smooth rubber, just a quarter-inch wide, and provides only thirty degrees of turning radius. The focusing range is bounded on either end with a hard stop. The short focusing throw undoubtedly speeds autofocus performance, but making small adjustments with manual focus is quite difficult. The lens is built with autofocus in mind.

A lens hood (model ALC-SH108) is available separately for the 18-55mm ƒ/3.5-5.6 DT. The hood is the circular type, and reverses onto the front of the lens for easy storage.

Alternatives

Sony 18-70mm ƒ/3.5-5.6 DT ~$200
While the new kit lens doesn't reach 70mm, the new 18-55mm is superior to the 18-70mm with regard to sharpness, resistance to chromatic aberration and corner shading, such that the improved image performance won't make you pine for the extra 20mm of reach.

Sigma 17-70mm ƒ/2.8-4.5 DC Macro ~$350
Sigma offers the 17-70mm ƒ/2.8-4.5 in the Sony mount, offering a wider, longer, and faster lens option than the Sony 18-55mm. The Sigma is slightly sharper, about the same with CA and distortion; corner shading is a bit more distinctive, particularly at 17mm.

Tamron 17-50mm ƒ/2.8 XR Di II LD Aspherical IF SP AF ~$450
Tamron's 17-50mm ƒ/2.8 is justifiably popular, offering a constant ƒ/2.8 aperture in a kit-lens range of focus lengths. And it's sharp at ƒ/2.8, sharper than the Sony when matched in the same focal length and aperture; CA performance and corner shading are quite low. Distortion is a bit of a mixed bag, perhaps a bit less predictable than the Sony, but otherwise, the Tamron is the stronger performer.

Conclusion
For a kit lens, the Sony performs quite well - sharp wide open at 18mm, reaching its best performance when stopped down to ƒ/5.6 or ƒ/8. It's a definite improvement over the previous kit lens, the 18-70mm ƒ/3.5-5.6 DT.

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.