Sony A58 Tech Info
Sony A58 Technical Info
by Mike Tomkins
Sensor and image processing. 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 16.1 megapixel cameras, the Alpha A58 features a 20.1 effective megapixel sensor. The sensor is mounted on a movable platter that allows it to provide for SteadyShot Inside image stabilization.
Total resolution of the chip is 20.4 megapixels, and despite the bump in resolution (accompanied by a 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 3200 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 A37 either.
Of course, that will in part be due to the higher-resolution image sensor, and all those extra pixels which must be handled in capturing, processing and writing each image. Still, the 4.9 frames per second burst rate which we measured in our lab is quite a bit less than the 5.5 fps we found for the A37. It's only a little more than half the 8 fps claimed by Sony for the A57, which hasn't been through our lab.
Buffer depth for the Sony A58 in our lab testing was eight fine JPEG, six RAW, or five RAW+JPEG frames. The A37, by contrast, managed ten JPEG fine, seven RAW, or six RAW+JPEG frames. And Sony rates the A57 as capable of up to 25 fine JPEG, 21 RAW, or 19 RAW+JPEG frames.
Note that all of these figures 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 claimed rate of up to 12 or 7 fps respectively. The A58 saves at a lower resolution of 5 megapixels in tele-zoom mode, but Sony claims it is capable of up to 8 fps at this resolution.
EVF and LCD. One area in which the Sony A58 clearly bests 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 very generous dioptric correction range of -4.0 to +4.0 m-1 as in the A38, and a precise 100% field of view as seen in both earlier models.
Unfortunately, that upgrade may not be the only thing persuading you to take more advantage of the viewfinder. 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. That's below both the size used for the A57, and the average for a modern interchangeable-lens camera.
And in place of the high-res, reduced glare Xtra Fine TruBlack display used in the A57, the Sony A58 uses a lower-res 460,800 dot Clear Photo LCD. That's the same tech as in the A37, albeit with double the resolution of that camera's monitor.
Autofocus. 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 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. 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 Lock-on function allows the camera to better determine when the same subject has arrived under an AF point, and thereby to resume tracking the subject.
Exposure. 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.
Flash. The built-in flash strobe is also relatively little-changed. It still has a guide number of 10 meters at ISO 100, but this is now accompanied by a rather wider 16mm coverage. Recharging is a little slower, at 4 seconds according to Sony, where the A57 could recharge its strobe in 3 seconds. X-sync is at 1/160 sec., and the A58 supports wireless flash.
Hot shoe. As noted previously, the external flash hot shoe 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.
If you have Konica Minolta-style strobes, you can still use them, but you'll need to buy an optional adapter.
Features. 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 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.
Creative effects. Of course, the A58 also includes a variety of other creative options, all of which were present in its predecessor. The camera's 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 Sony's Dynamic Range Optimizer function that tweaks the tone curve automatically or manually to bring out shadow detail without sacrificing highlights. Finally, there's a Sweep 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. 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 maximum, rather than the 28 Mbps of the earlier camera.
Like the A57, the Sony A58 provides 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. You can also attach the ECM-XYST1M mic shown on the right, which mounts on (and interfaces via) Sony's Multi Interface Shoe. The A58 isn't compatible with the higher-end XLR-K1M Multi Interface Shoe-mounted mic, though.
Connectivity. In addition to 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, Micro USB port and Micro HDMI high-def video port.
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. Note however that support for Sony's RMT-DSLR1 wireless remote has been dropped.
Storage and battery. 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 7.2v 1600mAh rechargeable battery pack.
It's the same pack used in the A57, but according to Sony's rating, battery life has been improved dramatically. The Sony A57 was CIPA-rated to 550 shots through the viewfinder, or 590 shots with the LCD monitor. The A37 -- which used a different pack -- lagged even further behind, with 450 viewfinder or 500 LCD shots.
The claimed 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. And Sony's claim gels well with what we found in the field: battery life from the A58 is very good, especially for an EVF-equipped camera.
Accessories. Alongside the camera, Sony also introduced several new accessories. A wired remote commander -- the RM-VPR1 -- connects to the multi-terminal USB port, and is priced at around US$65.
For the multi-interface hot shoe, there's 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 costs US$150, and has been available since 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).