Sony A77 Optics
Sony A77 Optics
The Sony A77 features a bayonet lens mount, which accommodates a range of Sony and Konica Minolta lenses. The Sony A77 optionally comes bundled with a Sony DT 16-50mm F2.8 SSM standard zoom lens, which our sister site SLRGear.com felt to be a capable walk-around zoom. The lens features a built-in focus motor for fast, quiet autofocus, and is designed to be used with subframe Sony SLRs. For detailed test results, see our review of this lens on SLRgear.com.
A small button on the front of the camera releases the lens from its mount, so it can be turned and removed. The A77's CMOS image sensor is smaller than a frame of 35mm film, so the angle of view at any given focal length will not be the same as on a 35mm camera. To find the approximate 35mm equivalent focal length, multiply the focal length of the lens by 1.5. (Thus, a 16-50mm lens will provide about the same view as a 24-75mm lens on a 35mm camera.)
The Sony A77 provides both manual and automatic focus control modes, set by the Focus Mode dial on the left side of the camera's front panel, unless the lens itself has a Focus Mode switch. If there's a duplicate switch on the lens, then both must be set to allow autofocus; that is to say that if either control is set to manual focus, then the setting of the other control will be ignored. The dial on the body provides more control than that on the lens, however. Instead of simply enabling or disabling autofocus, it's also used to set the AF mode to either Single-shot AF, Automatic AF, or Continuous AF. Single-shot sets focus with each half-press of the Shutter button, while Continuous mode is constantly adjusting the focus, whether the Shutter button is pressed or not. The Automatic setting will lock focus on a still subject or continually adjust focus on a moving subject, for as long as the Shutter button is halfway pressed.
The Function button provides access to Autofocus Area options, of which there are four choices: Wide, Zone, Spot, and Local. The default option is a 19-point Wide Focus area, with AF point locations indicated by small squares visible through the electronic viewfinder or on the rear-panel LCD display. Note that of the 19 AF points, only eleven utilize a cross-type sensor sensitive to detail in both the horizontal and vertical axis, with the other eight line-type sensors being sensitive to detail in one direction only. Wide AF bases its focus on the most prominent subject detail in the portion of the image that falls within the AF brackets, and the A77 can indicate which individual AF points achieved a focus lock by highlighting those points in green on either the electronic viewfinder or LCD while the shutter button is half-pressed.
In Zone mode, the AF points are addressed in one of three groups: either a group of seven points in a column near the horizontal center of the frame, or one of two clusters of six points in the left or right of the frame. The camera will still automatically choose one or more points at which to achieve a focus lock, but it will restrict itself solely to point in your chosen group while doing so. In Spot mode, the A77 uses only the centermost AF point, and only this point is indicated by a square target box in the center of the viewfinder or live view display. Finally, Local mode is Sony's terminology for a manual AF area selection, also known as Flexible Spot in some earlier models. This lets you manually set the main AF point by using the Multi-controller to highlight one of the 19 available AF points. The active AF area is given a bolder line in the viewfinder and live view displays, and is again highlighted in green upon focus lock as a visual reminder of which point was manually selected.
A couple of the more unusual features of the Sony A77 are its Face Detection and Smile Shutter functions. Face Detection can detect up to eight faces simultaneously within the image frame, and adjusts focus, exposure, image processing, and flash output. Detected faces are indicated with gray frames, which turn white when they fall under an autofocus point. When focus lock is achieved, the camera indicates which faces it feels were correctly focused with a green frame. When no faces fell under a phase detection sensor, the A77 reverts back to showing the AF points that achieved a lock, instead. Optionally, you can program the camera to recognize the faces of up to eight specific individuals, who will then be prioritized over other faces whenever they're recognized in the image frame. Smile Shutter, meanwhile, can be used to trip the shutter automatically when a smile is detected. You can adjust the "sensitivity" of Smile Shutter to either "Slight", "Normal", or "Big" smile, and a gauge at the left of the screen shows the degree of smile that the A77 is currently detecting, along with a mark indicating the point at which the shutter would be triggered.
A depth-of-field preview button can be found adjacent to the grip, at the base of the lens mount. When held in, the A77 stops down its aperture to the selected value, allowing preview of the depth of field available in the scene. The function is rather more useful than in the typical SLR, however, in that while the view through the electronic viewfinder will dim while the aperture is stopped down beyond the camera's ability to correct for, the camera otherwise adjusts preview sensitivity to attempt to show the image with correct brightness. This makes it quite a bit easier to gauge depth of field with small apertures in good light (but perhaps makes the preview image grainier in low light conditions).
Sony A77 AF Assist
The Sony A77 has a dedicated AF assist lamp, based around a bright red LED that projects a vertical line pattern, providing some high-contrast edges for easier and more accurate focusing on nearby subjects in dim lighting. This has two advantages over the more common flash-based AF assist on cheaper SLRs: it functions regardless of whether your flash strobe is raised, and doesn't dazzle your subject quite as much, so it's less likely to cause a blink.
Sony A77 Anti-Shake
The Sony A77 also employs Sony's SteadyShot Inside anti-shake technology, which uses a highly sensitive accelerometer, and a moveable platter on which the CMOS sensor assembly is mounted. Together, these allow the A77 to counteract camera movement with movements of the image sensor, rather than the more common approach of moving an optical element inside the lens.
Depending upon shooting conditions and the lens type attached, Sony claims that the SteadyShot Inside anti-shake system in the A77 provides anywhere from a 2.5 to 4.5-stop reduction in the blurring produced by camera shake. Translating that into real-world shutter speeds, a two-stop improvement means that a shutter speed of 1/30 second would give you the same resistance to blur from camera shake that a speed of 1/120 would without anti-shake. A 4-stop improvement would mean you could shoot as slow as 1/6 second and get the same results (blur-wise) as when shooting at 1/120 second unaided. Even the lower end of the specified range of effectiveness means a pretty significant improvement in one's ability to hand-hold long exposures.
Sony A77 Anti-Dust Technology
To help combat dust particles on the CMOS sensor from changing lenses, Sony has included both an anti-static coating on the low-pass filter and uses the sensor shift mechanism to automatically shake dust free each time the camera is shut off. There is also a manual cleaning mode, where the camera triggers a longer burst of sensor shift shaking. We've generally found dust-removal systems based on cameras' anti-shake systems less effective than those that use an vibrate the sensor ultrasonically, but it bears noting that no dust removal system completely eliminates the need for occasional manual sensor cleaning.
Sony A77 Optical Test Results
Below are the results of our optical tests of the Alpha A77 with the Sony DT 16-50mm f/2.8 SSM kit lens. The test images shown on most other pages of this review were taken with very sharp references lenses, so we use this page to explore kit lens quality.
Lens Test Results
Good performance with the 16-50mm f/2.8 lens.
|16mm @ f/8||35mm @ f/8|
|50mm @ f/8||2x "Smart Teleconverter"|
The Sony Alpha A77 is available bundled with the DT 16-50mm f/2.8 SSM lens. This lens possesses a typical optical zoom ratio of about 3.1x, but is wider than most with a 35mm equivalent focal range of about 24-75mm. Performance at wide-angle was good though overall detail is just a touch soft at f/8. Some blurring is visible in the corners, as well as some minor coma distortion, though chromatic aberration is very low because the camera suppresses it. There's also a small amount of flare around the building's white surfaces. Performance at 35mm was also quite good, with very good contrast and good sharpness across most of the frame. Results at the 50mm setting were similar, just a hint soft in the center and a bit softer in the corners. The Sony A77 offers 1.4x and 2x "Smart Teleconverter" digital zoom settings, which just crop so there's no image degradation, though the resulting images are smaller. Still, with a total of 24 megapixels on tap, the cropped images are quite useful. (1.4x results in 12-megapixel images, while 2x produces 6-megapixel files.) Overall, a good performance from a premium kit lens.
A larger than average sized minimum coverage area, with good detail. Flash was a bit bright but throttled down reasonably well, though lens casts a shadow.
|Macro with 16-50mm
kit lens (45mm @ f/8)
|Macro with Flash|
As with zoom performance, the Sony Alpha A77's macro performance will depend entirely on the lens in use. However with the 16-50mm kit lens set to 45mm, the Sony A77 captured a larger than average sized minimum area measuring 4.76 x 3.18 inches (121 x 81 millimeters). Detail was pretty good, just a touch soft in the center of the frame at f/8, but corners weren't much softer. (Most lenses have some softening in the corners at macro distances, so the 16-50mm lens did better than average here.) Auto white balance was quite warm and yellowish with our ambient lighting, though. The flash did a pretty good job throttling down, though the lens casts a shadow, leading to a very uneven exposure.
Higher than average geometric distortion at wide-angle.
|Complex barrel distortion at 16mm is about 1.0 percent|
|Pincushion distortion at 50mm is about 0.2 percent|
The Sony Alpha A77's 16-50mm kit lens produced about 1.0 percent of complex barrel distortion (moustache-shaped) at wide-angle, which is higher than average and noticeable in some of its images. At the telephoto end, we measured just under 0.2% pincushion distortion, which is not very noticeable in images. 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 and Corner Sharpness
Low to moderate chromatic aberration in JPEGs. The lens produced some soft corners at both zoom settings.
|16mm@f/2.8: Upper left
Softness: Moderate blurring
|50mm@f/2.8: Upper left
Softness: Slight blurring
C.A.: Very low
Softness: A touch soft
Chromatic Aberration. Chromatic aberration in the corners with the Alpha A77's 16-50mm kit lens at wide-angle (16mm) and maximum aperture was moderate in terms of the number of pixels, so the effect was noticeable in a few shots. At full telephoto (50mm) and maximum aperture, chromatic aberration was less noticeable, with only faint coloration.
Corner Softness. Wide-open at full wide-angle, the 16-50mm kit lens was moderately soft in the top left corner, while other corners were considerably sharper. The softness didn't extend very far into the frame, though, and the center was quite sharp. At full telephoto, all four corners showed only slightly blurring, while the center was just a touch soft with lower contrast than wide-angle. You can also notice some minor vignetting (corner shading) from the darker corner crops, but it's really quite low.
|16mm@f/8: Upper left
C.A.: Moderately low
Softness: Slightly soft
|50mm@f/8: Upper left
Softness: Slightly soft
C.A.: Very low
Chromatic Aberration. With the lens stopped down to f/8, chromatic aberration in the corners at wide-angle (16mm) was moderately low, better than wide-open, and in the center it was quite low. At full telephoto (50mm), chromatic aberration was again low in the corners, and very low in the center.
Corner Softness. Corner sharpness improved at wide-angle at f/8, though corners were still a bit softer that the center. Interestingly, at telephoto some corners were a bit softer stopped-down to f/8 than there were wide open, though the center was fairly sharp. Vignetting was low at wide-angle, and negligible at telephoto.
Overall, a good performance for a kit lens, especially considering the A77's resolution.
When shooting in JPEG mode, the Sony Alpha A77 includes the ability to automatically correct or improve geometric distortion, chromatic aberration, and lens shading (vignetting) from supported lenses, as images are captured.
|Barrel distortion at 16mm is less than 0.2 percent|
|Pincushion distortion at 50mm is lens than 0.1 percent|
Above, you can see with Distortion Correction enabled (set to Auto), the kit lens shows significantly less distortion (<+0.2% at wide-angle, <-0.1% at telephoto) than with it disabled (+1.0% at wide-angle, -0.2% at telephoto). The default setting is Off.
|CA Correction Auto||CA Correction Off|
|16mm@f/2.8: Lower right
|16mm@f/2.8: Lower right
C.A.: High and bright
|50mm@f/2.8: Lower right
|50mm@f/2.8: Lower right
C.A.: Also low
Above, you can see a significant increase in chromatic aberration at wide-angle with CA Correction disabled, though the difference at telephoto is minimal because CA is low at telephoto to begin with. The default setting for this correction is Auto.
|16mm @ f/2.8|
Mouse-over the links above to see the difference Peripheral Shading correction makes at wide-angle when wide-open at f/2.8 (the worst-case scenario for most lenses). The default setting is Auto.
The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Sony Alpha SLT-A77 Photo Gallery .
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