Sony A58 Optics

Optical Zoom
A typical zoom ratio of ~3.1x for a kit lens, with average performance.

The Sony A58 is available bundled with a DT 18-55mm f/3.5-5.6 SAM II "kit" lens. This lens possesses a typical optical zoom ratio for a kit lens of about 3.1x with a 35mm equivalent focal range of about 28-82mm.

Sharpness and contrast at full wide angle (18mm) are fair at f/8 over most of the frame, and chromatic aberration isn't an issue since the camera suppresses it (see below), however some flare is visible around the building's white surfaces. It's difficult to judge corner performance here because of the depth in this scene, so we'll do that below. At full telephoto (55mm), overall performance is also fair, with decent sharpness in the center but slightly soft corners, as well as some flare.

See sections below for comments on macro, geometric distortion, corner softness, performance wide open, chromatic aberration, etc.

Digital Zoom
The A58 offers three types of digital zoom. Sony's "Clear Image" digital zoom is available at 2x magnification, standard digital zoom up to 4x, and Smart Zoom is available where the camera crops away the unused portion of the image when a lower resolution is selected. You can combine the various digital zooms as well.

Clear Image Zoom does a pretty good job at 2x magnification, though there's still a noticeable loss of fine detail and some visible aliasing artifacts, despite Sony's claim of being "nearly equivalent" to optical zoom. 4x standard digital zoom is much softer, as you'd expect. It's difficult to tell given the lack of fine detail in this scene at these zoom levels, but it's probably best to avoid using digital zoom altogether and instead crop, upsize and sharpen as required during post processing.

Macro
A smaller than average minimum coverage area, with good detail. Flash throttled down reasonably well.

As with zoom performance, the Sony A58's macro performance will depend entirely on the lens mounted. However with the 18-55mm kit lens set to 55mm, the A58 captures a minimum area measuring 2.30 x 1.53 inches (59 x 39 millimeters), which is slightly smaller than average for a kit lens. Performance is very good in the center at f/8 with strong detail, though the corners and edges of the frame are quite soft. (Most lenses have some softening in the corners at macro distances.) The flash did a fair job throttling down at minimum distance resulting in slight overexposure, and coverage was somewhat uneven. The flash had no trouble clearing the lens as there is no detectable shadow.

Geometric Distortion
Higher than average geometric distortion at wide angle, but almost no distortion at telephoto.

With the 18-55mm kit lens, the A58 produces JPEGs with about 1.1 percent barrel distortion at wide angle, which is higher than average and quite noticeable. At the telephoto end, there's only about one pixel's worth of wavy distortion, which is difficult to detect. This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).

Chromatic Aberration, Corner Sharpness & Vignetting
Low levels of C.A. (the camera suppresses it). The lens produces some soft corners.

Chromatic Aberration. Chromatic aberration in the corners with the A58's 18-55mm kit lens at wide angle (18mm) is moderately low, and the center of the image shows very little C.A. The camera does a pretty good job at suppressing much of the lateral C.A. produced by the lens (see below). At full telephoto (55mm), C.A. is lower in the corners, though the center shows a bit more than at wide angle (possibly the result of a slight focus difference).

Corner Softness. Wide open at full wide angle, the 18-55mm lens that came with our A58 is soft in all four corners, with the upper-left and lower-right corners being the softest, even showing some image doubling. Softness doesn't extend very deep into the frame, though, and the center has good sharpness and contrast. At full telephoto, the upper-left corner is quite soft while the other corners are sharper, though softness extends fairly deep into the frame. The center isn't quite as sharp as wide angle, with lower contrast.

Vignetting. Moderate vignetting (corner shading) is noticeable at full wide angle, as indicated by the darker corner crops. Corners and edges also show a cool, bluish tint, even in RAW files. We've seen shifts in color along the periphery of the frame before, but it's pretty obvious here. We'll try to determine if it's caused by the kit lens or if something else such as the sensor's microlenses are responsible. Vignetting is negligible at full telephoto, with no discernible color shift.

f/8. "Stopped-down" to f/8, corner sharpness at wide angle improved noticeably compared to wide open at f/3.5, though diffraction makes the center a little softer. At full telephoto, corner sharpness didn't really improve much compared to f/5.6, though the center showed better contrast. Although improved compared to wide open, vignetting and the bluish tint are still visible in the corners at f/8 at wide angle.

Overall, a typical performance for an inexpensive kit lens (which is to say not great). It's a good start and a great value when bought as part of a kit, but to get the most out of the Sony A58's 20-megapixel resolution, you'll want to invest in some better glass.

Lens Corrections

When shooting JPEGs, the Sony A58 includes the ability to automatically compensate for geometric distortion, chromatic aberration, and lens shading (vignetting), as images are captured.

Geometric Distortion

Above, you can see the corrected geometric distortion from the 18-55mm kit lens is very low, with less than 0.1 pincushion distortion at wide angle (slightly over-corrected), and about the same very low wavy distortion as before at telephoto. Note however than some of the wide-angle shot is cropped away during the correction process. The default setting for this compensation is Off (at least with the 18-55mm lens).

Chromatic Aberration

Above, you can see significantly higher lateral Chromatic Aberration at wide angle with Chromatic Aberration Compensation disabled, though the difference at telephoto is minimal because C.A. is low at telephoto to begin with. The default for this setting is Auto.

Lens Shading

Mouse-over the links above to see the difference Lens Shading Compensation makes at wide angle when wide open at f/3.5 (the worst-case scenario for most lenses). As you can see, corners are brightened without affecting brightness at the center, though some fall-off is still left behind in the corrected image. The default setting is also Auto.

Coverage
Excellent accuracy from the EVF and LCD monitor.

The Sony A58's electronic viewfinder and LCD monitor both show 100% coverage in record mode with our Sigma 70mm f/2.8 prime lens. This is excellent performance, though not a surprise given the image is derived from the main imaging sensor.