Sony Alpha SLT-A55 Camera Review
Performance - How well does it take pictures?
Ultimately, it is the image quality that makes a camera worth buying. For an ILC, image quality greatly depends on the lens used. While color, noise, contrast and exposure are properties of the camera, distortion, vignetting and chromatic aberrations are properties of the lens. Sharpness depends on the weakest link. So, the camera cannot capture more details than the lens lets through. Conversely, it is possible for a lens to transmit more details than the sensor can capture.
The most common mistake people do with buying a DSLR is to not spend enough on the lens. Well, the same is true of ILCs. This is the easiest way to be disappointed at image quality. This Sony is sold as a kit labeled SLT-A55VL which comes with a rather low-quality 18-55mm F/3.5-5.6 plastic-mount lens. This keeps the total cost low just as it does image quality. The SLT-A55 is capable of much higher quality, for this reason indoor quality tests here were performed with a Minolta 50mm F/1.7. An affordable modern equivalent would be the Sony Alpha SAL50F14
Sony Alpha SAL50F14.
The 16 megapixels Sony CMOS sensor in the SLT-A55 has an excellent resolving power when combined with a sharp lens. This can be seen in the indoor crops page. The base ISO of 100 is completely noise-free and usable for prints up to 24" x 16". ISO 200 and 400 are nearly identical, which is expected from an APS-sized sensor camera like this one. From ISO 800, noise picks up slowly but images quickly get softer. This is a sign of aggressive noise-reduction, which affects print sizes similarly to increased image noise. There are two noise-reduction settings on the A55: Auto and Weak. The one shown in our samples is Weak. Auto is less predictable as it chooses between weak and strong NR based on multiple factors. These include ISO, drive mode and camera temperature. Since NR cannot be turned off, images from RAW files can show more details along with more noise at higher ISOs. The approach chosen by Sony fits their target market here but advanced users can use RAW to get around it.
ISO 1600 is easily usable to print an 8" x 12" but ISO 3200 is were details seriously get destroyed. Still, small 4" x 6" prints look great at ISO 3200 and 6400 and even ISO 12800 is usable, just barely. The A55 also has Multi-Frame ISO from 100 to 25600. This is a system where the camera processes continuous shots to produce a lower-noise result. The two catches with this is that subject motion will show up as strange artifacts and that self-timers cannot be used in Multi-Frame ISO. The review samples include a comparison page between Multi-Frame and standard ISO settings. Briefly, there seems to be a slight advantage starting at ISO 1600, eventually reaching roughly one full stop.
Metering from the Sony Alpha SLT-A55 is rather good. It rarely over-exposes, erring on the conservative side. There were some rare occasions of instability when the meter would swing between two values in a static scene but nothing to worry about except for writing digital camera reviews. In any case, the meter never moved more than 1/3 EV. There is no way to make the A55 use half-stops either.
The automatic white-balance of the A55 is a below average for a modern camera. Outdoors, WB is good most of the day. As light levels drop, it tends to leave a bluish tint though. Indoors, it gets some lights spot on and others are left with a slight warm cast. Given typical conditions, the warm cast is much less disturbing than the bluish tint which can look quite unnatural. Preset white-balance options behave as expected and can be fine-tuned to fit most situations. As expected, custom white-balance is spot on, at least when things fall in the camera's measurement range. At dusk, when the sky is cobalt-blue, the maximum color-temperature can easily be exceeded. In this case, the A55 displays an error message and sets its the WB to 9900K. On the warm side, the minimum is 2500K, which is much harder to exceed. At least, it is easy to know when WB is off, since the EVF previews it correctly.
Color accuracy is very good when the Creative Style is set to Standard. In this case, some colors were slightly under-saturated but +1 of saturation fixes the problem without producing unrealistic images. Other styles play a little with color saturation but hue remains close to reality. Regarding other image parameters, the defaults are reasonable but a little soft. Boosting sharpness by +1 makes results more pleasing without any visible artifacts. Remember that since parameters are relative on the A55, standard sharpness in Landscape style is actually sharper than +1 in Standard.
Dynamic range is excellent on the A55, even with the DRO features turned off. This camera manages to cope well with high-contrast scenes. When the DRO is on Auto, it uses the light meter to determine how much contrast reduction is needed to capture most of the scene. It works well enough, sometimes boosting shadow noise but generally producing nice-looking images. The DRO can also be set to one of five levels which represent a fixed change in contrast. Using a too-high DRO level can easily result in a flat-looking scene, so it is preferable to set it on Auto when needed.
As expected from an ILC, this camera shows image quality that matches and even exceeds most similarly-priced DSLR cameras. The most important remaining question is: Does it close the gap between SLDs and SLRs? The answer undoubtedly comes down to speed.
While many SLDs have already shown similar image quality, they have so far fallen short of DSLRs in terms of speed, mostly due to autofocus speed and display lag. Enter the Sony Alpha SLT-A55, an SLD with phase-detection AF system that has to work with about 70% less light than its DSLR counterparts to take this on.
Power on time is in the order of 2 seconds, which is the time it takes for an image to form on the EVF. A small detail which should be obvious is that the A55 cannot be used to frame or focus a shot before it has completed its power on cycle. This is true of all SLDs but not SLRs, since an OVF shows something as long as there is no lens-cap on. Shutdown starts immediately and takes just under 2 seconds to shake-off dust from the imaging sensor.
In good light, focusing is nearly instant. Less than ¼s as long as focus is not way off to start with. This shows that the A55 itself can focus extremely fast. When focus is initially far from where it should be, the lens becomes an important contributor to AF speed. The kit lens particularly has a very slow SAM motor that can take over one second to move across the focus range. By contrast, the Minolta 50mm F/1.7 which does not include a focus-motor, is roughly twice as fast. To alleviate this, the A55 has a feature called Eye-Start AF. When active, Eye-Start AF approximately focuses each time the EVF's proximity-detector is triggered. It greatly reduces focusing time at the expense of battery life and audible autofocus noise. When hanging from the neck-strap, Eye-Start AF constantly triggers due to the camera's proximity to the wearer's chest. We assume this also drains the battery faster, but after hearing the AF motor a few times too many, that feature was turned off. When Konica-Minolta originally implemented this feature, they had a grip-detector as well which made sure the camera was held before triggering autofocus.
In low light, focusing naturally slows down. Since autofocus is performed with the lens wide open, just like on an SLR, it slows down in proportion to the maximum aperture at the current focal-length. Take the kit lens again as an example, at 18mm the maximum F/3.5 means it slows down for a small fraction of a second, at 55mm the maximum F/5.6 aperture slows it down by a whole second. The 50mm F/1.7 on the other hand always takes just a fraction longer in low-light and still remains reasonably fast.
Overall, the Sony SLT-A55 shows very good autofocus speed but seems more vulnerable to lenses with small maximum apertures than usual. It still focuses faster than all SLD cameras reviewed here but, in low light, it does lag behind quite a few DSLRs. Between the SLT-A55 and an entry-level DSLR, the difference in auto focus speed is noticeable but not that much.
The all-important shutter-lag is very short and is followed by a quick but noticeable black-out due to the shutter mechanism. Shot-to-shot speeds hover around 1/3s but just remember to turn off Instant Review, otherwise it takes almost 1s between shots. The continuous drive easily reaches 7 FPS and the camera manages to focus continuously throughout an entire burst. It also reaches 10 FPS with the restriction that AF-C is only possible at the maximum aperture. While the shutter-lag and shot-to-shot speeds are reasonable, continuous drive speed is stellar.
The Eye-Start sensor rapidly switches between the EVF and LCD. Entering and exiting Playback mode takes about one second. Playback mode itself is reasonably fast: Switching between images is instant; Zooming into an image takes about 1 second; and Pan-and-zoom is quite responsive. Actually, the camera reacts almost instantly when any button or dial is pressed.
Super Steady Shot has always been one of the most effective image stabilization system and the one built into the Sony Alpha SLT-A55 performs just as well. It is highly reliable and consistently manages more than 2 stops of stabilization. Even 3 stops is quite common. Stabilization is functional in video mode but only to a maximum of 9 minutes, as it may cause the camera to overheat. The 5-level shake-o-meter which is visible on the EVF and LCD helps get a stable image by notifying the photographer when vibrations are low.
The battery used in the SLT-A55 manages 330-shots per charge (CIPA Standard) using the EVF. Despite the much larger LCD, battery-life is longer with it. The only guess as to why is that the EVF's circuitry consumes more energy than the LCD's back-light. These battery life numbers also include the power needed to keep the GPS working every 15 seconds.
Performance - How well does it shoot video?
The Sony Alpha SLT-A55 records full 1080p HD video with stereo sound. Sound can be recorded from the built-in pair of microphones or an auxilary audio input connected via mini-jack. The internal sound is a little muddled, as usual for such small microphones, and easily picks up noise from the autofocus mechanism. Since one of the headline features of the SLT-A55 is continuous AF during video recording, it is probably wise to invest in an external microphone.
Videos at 1920x1080 @ 30 FPS are stored in MTS files using the AVCHD codec. These MTS files are obscurely located below a folder called private several levels deep. While the file-system used on SDHC files is limited to 2GB per file, the A55 can split videos into multiple files and record continuously up to 29 minutes or 9 minutes if stabilization is enabled. The MTS files can be read by the free VLC player but are not generally supported yet.
The more common and easily understood MPEG-4 format is used when movie mode is set to 1440x1080 @ 30 FPS. This peculiar mode records video with rectangular pixels, called anamorphic format, to cover a 16:9 wide-screen aspect ratio with less pixels. This obviously causes a reduction in horizontal resolution. Files are stored along images in this case.
Video quality from the SLT-A55 is truly excellent, showing extremely clean and detailed footage with virtually no artifacts. Motion is rendered fluidly. Continuous autofocus during video actually works much better than on most digital cameras. It can track camera motion and some moving subjects closely. For fast motion, there is a short lag while the camera catches up. When the lens and camera are both set on autofocus, AF-C is used. Focus is manual otherwise.
The SLT-A55 is a rare ILC that can shoot videos at eye-level thanks to the superb EVF. The EVF also accurately previews video framing, color and exposure. Exposure-Compensation can be adjusted while filming but other settings remain on automatic regardless of the current exposure mode.
When the record button is pressed, there is a one second delay until video recording starts. When it is pressed again, there is a one second delay until video recording stops. The former is mostly unfortunate and is probably caused by the lack of a video mode to have the sensor ready for filming. We have seen far worst but this is not ideal by any stretch of the imagination.
The Sony Alpha SLT-A55 is an innovative camera that provides a unique compromise between DSLRs and other SLDs. Most importantly, this camera closely matches the image quality and performance of modern entry-level DSLRs. Its translucent mirror also gives it the unique ability to use phase-detection autofocus during video-recording and continuous-drive up to 10 FPS. While it is clear that some of its features and design is aimed at more novice photographers, the SLT-A55 provides an excellent usability experience through its top-notch EVF.
The truth is that there is very little to criticize the A55 on. Noise-reduction is stronger than ideal and the sensor has to work a little harder than on a standard DSLR, but the difference is hardly significant for most uses. Automatic white-balance is probably the only sub-par aspect but it can often be corrected using presets or custom white-balance. Speed is generally good, although some numbers were not outstanding, the A55 never actually feels slow.
The EVF experience is enough to promise a bright future for SLT cameras. Its bright and large eye-level view is unmatched by any DSLR. This view, which provides an accurate preview of exposure, color, white-balance and focus, is much more useful than an OVF and removes the need for chimpingLooking at the display on a digital camera after taking a picture to see how it came out.. It takes a while to break the habit but, once done, is a liberating experience. For fast action, there may still be a reason to prefer an OVF, but it is a small one. The HUD on the A55 also helps keep the camera longer at eye-level, meaning taking pictures back-to-back faster than with most modern digital cameras.
Without a doubt, the Sony Alpha SLT-A55 deserves our highest rating and we really cannot wait to know how SLT cameras will evolve from here. For now, the A55 is a very compelling DSLR-replacement, particularly for new photographers and video enthusiasts.
Sony SLT-A55 Facts
Mirrorless digital camera
|16 Megapixels Mirrorless (SLD)||ISO 100-25600|
|Sony A Mount|
Sensor-Size: 24 x 16mm
Actual size when viewed at 100 DPI
|2-Axis Built-in Stabilization||Full manual controls, including Manual Focus|
|0.46" Built-in EVF 1.4 Megapixels (0.73X)||Custom white-balance with 1 axis fine-tuning|
|Automatic Eye-Start sensor||Spot-Metering|
|2 Axis Digital Level||Hot-Shoe|
|Built-in Dust Reduction||Stereo audio input|
|10 FPS Drive, 35 Images||Lithium-Ion Battery|
|1920x1080 @ 30 FPS Video Recording||Secure Digital Extended Capacity|
|3" LCD 920K Pixels||Memory Stick Duo|
The Sony Alpha SLT-A55V is the variant of this camera which features a built-in GPS. In some markets, this is the only one sold. GPS stands for Global Positioning System and having one in a camera lets the camera record in EXIF fields where each photo or video was taken.
The A55V has a simple GPS which records position, altitude and direction. This feature may be turned on or off, but not much more. When on, the camera tries to find its position every 15 seconds and records whatever last position it found. This has several implications:
- If the camera is unable to find its current position, it will record the last known position. If the camera was off for a while, or transported underground, the location data will be considerably off. We have seen several examples of this going through Montreal's subway system.
- When moving fast, there may be a non-negligible distance traveled in the 15 seconds between GPS locks. This will also cause the coordinates to be off.
- The direction is recorded as the way the camera is moving, not where it is actually pointing, so it is of limited use.
All GPS systems have an expected precision, for the A55V it is quoted as 30 meters which should give close coordinates but may place the photo in front of the wrong property or the wrong side of the street. In practice it can manage better with more satellites but the positioning system is quite fragile. Buildings are problematic and there is no tracking indoors.
The SLT-A55V supports GPS-Assist data to increase precision and the time it takes to lock. This is data that must be regularly downloaded from Sony's site which shows the current position and paths of GPS satellites Once a month, more or less, the data must be refreshed and copied into the camera. It will then be able to find its position faster than without.
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