Sony A58 Preview

by Mike Tomkins
Posted 02/25/2013

In the first half of 2012, Sony launched two new Translucent Mirror-based cameras that together formed the entry-level to the company's interesting, SLR-alternative lineup, the Alpha A37 and A57. Just ten months or so later, the Sony Alpha A58 follows in their footsteps, ready to replace one or perhaps both models. Reports from Europe, where the new camera was first unveiled, suggested that both of last year's cameras will be replaced by the A58 in that market. Our current understanding is that in the US market, the A37 will continue to be offered alongside the newer Sony A58, at least for the time being.

Compared to its predecessors -- and especially, to the A57 that's being replaced in the US market -- the Sony Alpha A58 has several key changes. Some are clear improvements, others debatably so, and in a few areas the specifications have been dialed back somewhat from the previous model. Key changes include a higher-resolution image sensor, Organic LED-based electronic viewfinder, Sony's proprietary Multi-Interface hot shoe, and a significant improvement in battery life. Accompanying these are a plastic lens mount, a reduction in the burst shooting rate and the specification of the LCD monitor, and a video mode that lacks the higher-bitrate 1080p60 Full HD option of the Sony A57. Of course, these are only the most significant differences; there are a number of other changes, as we'll see.

Sony has created a slightly smaller, lighter body for the Alpha A58, but the physical differences between the new body and that which precedes it are actually fairly minimal. The most significant change is the aforementioned switch to a plastic lens mount, something we can't recall seeing on any digital camera of this class to date. (We've seen more than a few lenses with plastic mounts, but not digital camera bodies.) It should be noted that the surface which has been replaced with plastic isn't, we believe, a load-bearing surface. The bayonet behind the mount is likely what takes the load of the attached lens, and this is still made of metal.

The plastic portion of the mount, then, is simply the interface against the back of the mount on the lens -- but nonetheless, we do have concerns about its durability in the longer term. It's one thing to place a plastic mount on a lens, which receives wear only whenever that specific lens is mounted or removed, and another entirely to put a plastic mount on the camera body, which will be worn every single time any lens is mounted or removed. Of course, an entry-level camera won't be subjected to the frequent lens changes that a pro or enthusiast camera might be, and perhaps this is what Sony is banking upon.

Looking at the rest of the body design, the basic control layout is almost completely unchanged, with the exception of the fact that the exposure compensation and zoom buttons have switched places. The former now occupies prime real estate behind the shutter button, and the latter has been demoted to the rear panel. And on the rear, it's immediately obvious that the A57's bottom-mounted tilt/swivel LCD panel has been replaced by a new tilt-only display that's rather less versatile. On the top deck, though, there's Sony's new Multi Interface hot shoe, something we've only seen on a few of the company's more expensive cameras until now. The Multi Interface shoe provides not only for flash strobes, but also for other accessories such as external microphones, viewfinders, and more. It's a relatively young system so far, but offers quite a bit of scope for extending the A58's capabilities in the future.

Moving beneath the skin, the Sony Alpha SLT-A58 is based around a higher-resolution Exmor APS HD CMOS image sensor than those of its predecessors. Where the A37 and A57 were both 16.2 megapixel cameras, the Alpha A58 features a 20.1 effective megapixel sensor. Total resolution is 20.4 megapixels, and the sensor is mounted on a movable platter that allows it to provide for SteadyShot Inside image stabilization. And despite the bump in resolution (and corresponding decrease in pixel pitch), Sony has retained the same sensitivity range of ISO 100 to 16,000 equivalents for its new camera. Of this range, everything from ISO 100 to 3,200 equivalents is available under automatic control.

Perhaps explaining its ability to retain the same sensitivity range while increasing resolution, Sony notes that it has updated the BIONZ image processing algorithms used in the Alpha SLT-A58. The new algorithms apply variant levels of noise reduction and sharpening across the image, based on the degree of subject detail detected. According to the company, these algorithms are the same as those used in its flagship Alpha SLT-A99 model.

Note, though, that Sony says it's using the same algorithms, and not the same image processing hardware. That the Sony A58 is based around a less powerful image processor seems fairly clear from its burst-shooting performance, which not only trails the A57 by some distance, but also doesn't quite manage to match the capabilities of the previous entry-level model, the A37. Of course, that will in part be due to the higher-resolution image sensor, and all those extra pixels that must be handled in capturing, processing and writing each image. Still, the five frames-per-second burst rate is just a little less than the 5.5 fps reported by Sony for the A37, and well behind the eight fps of the A57. Buffer depth for the Sony A58 is said to be just seven fine JPEG, six raw, or five raw+JPEG frames. The A37, by contrast, managed 17 JPEG fine, seven raw, or six raw+JPEG frames, and the A57 allowed up to 25 fine JPEG, 21 raw, or 19 raw+JPEG frames.

All of these are at full resolution; in the tele-zoom mode the Alpha A58 falls in between the A57 and A37's performance, but does so because it records at significantly lower resolution. The A57 and A37 save tele-zoom images at 8.4 megapixel resolution, with a rate of up to 12 or seven fps respectively. The A58 saves at a lower resolution of five megapixel in tele-zoom mode, but manages up to eight fps at this resolution.

One area in which the Sony A58 should clearly best both of its predecessors is its electronic viewfinder. While the SVGA resolution of the A58's viewfinder is said to be the same as that of the finder in the A37 and A57, and the size of the display used to create the viewfinder image is similar, the Sony A58 now uses an organic LED panel in place of the LCD panel from the earlier cameras. It also has a wider dioptric correction range of -4.0 to +4.9 m^-1, while retaining the same 100% field of view.

And that upgrade may not be the only thing persuading you to take more advantage of the viewfinder. Sadly, the Sony A58's LCD panel has been downgraded in several ways, compared to that of the A57. (It does, however, better the display found in the A37.) We've already noted the lack of a tilt-swivel articulation mechanism, replaced with a tilt-only mechanism. This allows a viewing range from 135 degrees upwards to 55 degrees downwards, and so cannot provide for portrait framing. The display itself is the same 2.7-inch size used in the A37, rather than the later 3.0-inch diagonal of the A57. And instead of a high-res, reduced glare Xtra Fine Trublack display as in the A57, the Sony A58 uses a lower-res 460,800 pixel Clear Photo LCD. That's the same tech as in the A37, albeit with double the resolution of that camera.

Autofocus is largely unchanged in the Sony A58. As with both its predecessors, the new model uses a 15-point phase detection autofocus sensor, and as is standard for Sony's Translucent Mirror cameras, this is available at all times -- even during movie capture. Three points at the center of the array are still cross-types, sensitive to detail in both horizontal and vertical orientations. There's still no dedicated autofocus assist lamp, with the Sony A58 relying on its popup flash strobe to provide assist illumination. One change, however, is a new Lock-On Autofocus function. Our understanding is that this couples information from the phase-detection autofocus pixels with that from the main image sensor, allowing subjects to be tracked as they pass between autofocus points, or as they stray outside the area covered by the autofocus sensor. This allows the camera to better determine when the same subject has arrived under an AF point, and thereby to resume tracking the subject.

Although it has a dedicated autofocus sensor, the Sony SLT-A58 meters exposures using the main image sensor. It considers the scene as 1,200 separate zones, and offers a choice of multi-segment, center-weighted, and spot metering modes. The working range for metering is -2 to 17 EV, at ISO 100 with an f/1.4 lens. Shutter speeds on offer range from 1/4,000 to 30 seconds, plus bulb. In all respects, this is unchanged from the A37 and A57.

The built-in flash strobe is also relatively little-changed. It still has a guide number of 10m at ISO 100, but this is now accompanied by rather wider 16mm coverage. Recharging is a little slower, at four seconds according to Sony, where the A57 could recharge its strobe in three seconds. X-sync is at 1/160 sec., and the A58 supports wireless flash.

As noted previously, the external flash hotshoe has been entirely replaced. Gone is the Konica Minolta-derived proprietary hot shoe that's featured on most previous Sony Alpha cameras, replaced with the new multi-interface hot shoe. This not only supports standard flashes, but also integrates 21 additional pins embedded at the front of the shoe for interfacing all manner of accessories to the camera.

Like the Sony NEX-3N alongside which it was announced, the Sony A58 has an updated Auto Framing function. This examines pictures as they're captured, then decides if the composition can be improved. If so, the camera will crop the image so as to best match its internal composition rules, then use a pattern-matching digital zoom function to enlarge the image back to full resolution. The end result, suggests Sony, is an image that's more pleasing, yet not of obviously lower image quality to the photographer. Previously, Auto Framing worked only for portraits, keying off the camera's face detection functionality. In the Sony A58, it also works for non-portrait photos. According to Sony, it will now recognize the subject in macro and action photos, and crop to improve composition with these subjects as well.

Sony has has also retained its 'Clear Image Zoom' function, a 2x digital zoom that relies on the rather clumsily-named 'By Pixel Super Resolution' algorithms to upsample images to a higher resolution than that at which they were captured. Sony claims Clear Image Zoom to offer better results than competing digital zoom techniques because it uses pattern matching to improve the quality of the guessed data.

Of course, the A58 also includes a variety of other creative options, all of which were present in its predecessor. A Picture Effects function has 11 modes, and a total of 15 possible effects. These include options like Retro Photo, Toy Camera, and HDR Painting, catering to those who prefer to do their post-processing in-camera. There's also a High Dynamic Range mode that combines multiple shots in-camera to yield a single image with broader dynamic range, and a Dynamic Range Optimizer function that tweaks the tone curve automatically or manually to bring out shadow detail without sacrificing highlights, plus a panorama mode that automatically captures and stitches images as you sweep the camera past your chosen scene, then saves the result as a single panoramic image.

Video capture in the Sony A58 is also largely similar to that in the A57, but with one important difference, as noted previously. The SLT-A58's video capture still tops out at Full HD (1,920 x 1,080 pixels), but is now limited to a choice of an interlaced 60i or progressive-scan 24p capture rate at this resolution, instead of the progressive-scan 60p rate of the Sony A57. It also has a lower bit rate of 24 mbps max., rather than the 28 mbps of the earlier camera. Like its predecessor, the A58 caters for movie audio with both a built-in stereo microphone in front of the flash hot shoe, and a standard 3.5mm jack for stereo external microphones.

As well as the mic jack, there's a variety of other connectivity options behind rubber flaps on the left of the camera body, including a DC input, USB port, wired remote terminal, and high-def HDMI video output. Sony describes the USB port as a multi-terminal, and it accepts a new RM-VPR1 wired remote control that provides a remote shutter button with lock, a zoom control, and a video button. In the contours of the handgrip, a small window conceals both an infrared remote receiver (compatible with the optional RM-DSLR1 remote), and a self-timer lamp.

The Sony A58 includes a single card slot on which to store images and movies. It's compatible with either the relatively commonplace Secure Digital cards (including SDHC and SDXC types), or with Sony's proprietary Memory Stick PRO Duo and PRO-HG Duo cards.

Power comes courtesy of an NP-FM500H InfoLithium M rechargeable battery pack, the same used in the earlier camera. According to Sony's rating, though, battery life has been improved dramatically to CIPA testing standards. The Sony A57 was rated to 550 shots through the viewfinder, or 590 shots with the LCD monitor. The A37 lagged even further behind, with 450 viewfinder or 500 LCD shots. The improvement in the Sony Alpha A58 is night-and-day in this area, with 690 shots on the viewfinder, or 700 when framing with the LCD monitor.

The Sony Alpha SLT-A58 goes on sale in the US market from April 2013. Kit pricing for a bundle including an updated DT 18-55mm F3.5-5.6 SAM II zoom lens is expected to be in the region of US$600. The new lens is said to offer quieter autofocus, and better-controlled flare and ghosting.

Alongside the camera, Sony will also offer several new accessories. A wired remote commander, the RM-VPR1, will connect to the multi-terminal USB port, and will be priced at around US$65 when it ships this April. For the multi-interface hot shoe, there will be a new on-camera flash strobe, the HVL-F20M, offering wireless flash control, bounce capability, auto white balance compensation, and the ability to enable or disable flash by raising or lowering the flash head. The HVL-F20M flash strobe will cost US$150, and ship from May 2013. Finally, there are three new Alpha-mount lens options. From most affordable to most expensive, these are the aforementioned DT 18-55mm F3.5-5.6 SAM II zoom (US$220), the Carl Zeiss Planar T* 50mm F1.4 ZA SSM prime (US$1,500), and the updated 70-400mm F4-5.6 G SSM II with faster autofocus and reduced flare / ghosting (US$2,200).