Sony DSLR-A580 Optics
Sony A580 Optics
The Sony A580 features a bayonet lens mount, which accommodates a range of Sony and Konica Minolta lenses. The Sony A580 comes bundled with a Sony 18-55mm f/3.5-5.6 SAM kit lens, tested in our A560 review. The lens features a built-in focus motor for fast, quiet autofocus, and is designed to be used with subframe Sony SLRs. For additional 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 A580'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 50mm lens will provide about the same view as a 75mm lens on a 35mm camera.)
The Sony A580 provides both manual and automatic focus control modes, set by the Focus Mode switch on the left side of the camera body, unless the lens itself has a Focus Mode switch. If there's a duplicate switch on the lens, it takes over this function, and the one on the body serves no purpose. With whichever switch is applicable, you can select between Auto and Manual focus modes. The Function button provides access to additional AF modes and AF Area options. The Autofocus Mode option under the Function menu offers Single-shot AF, Automatic AF and Continuous AF settings. 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.
Autofocus Area also has three options available through the Function menu: Wide, Spot, and Flexible Spot (manual setting). The default option is a 15-point Wide Focus area, indicated by an array of square focus areas whose locations are indicated by small squares visible through the optical viewfinder. Note that of the 15 AF points, only three utilize a cross-type sensor sensitive to detail in both the horizontal and vertical axis, with the other 12 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 A580 can indicate which individual AF points achieved a focus lock by highlighting only those points in the optical viewfinder while the shutter button is half-pressed.
In Spot mode, the A580 uses only the centermost AF point, and only this point is indicated by a square target box in the center of the viewfinder. Finally, Flexible Spot mode is Sony's terminology for a manual AF area selection, and lets you manually set the main AF point by using the Multi-controller to highlight one of eleven AF points. (The remaining four points are considered to be assist points -- available for selection by the camera in Wide mode, but not for manual selection. The active AF area is briefly illuminated in the viewfinder upon focus lock as a visual reminder of which point was manually selected.
The Sony A580 also offers a Live View mode, although its manner of operation differs from those of most competing DSLRs. The A580 includes a secondary, low-resolution image sensor in its viewfinder housing, which allows it to use the same phase-detection AF sensor that's employed when framing images through the optical viewfinder, resulting in live view autofocus speeds that are just as fast. That's because the secondary sensor negates the need for the additional mirror flips required for phase detection AF in most other Live View implementations. The majority of competing DSLRs must either drop the mirror, focus with the phase detection sensor, and then raise the mirror again before taking a shot in Live View mode, or they must employ a slower contrast-detect autofocus method using data from the main image sensor. Since the image sensor feeding the A580's live preview is located above the mirror, the mirror stays down until the final exposure, exactly as it does in optical viewfinder mode. The downside, though, is less accuracy in framing images, since the secondary sensor only offers around 92% frame coverage. Also, because the optical path for focusing is different than that for capture, there can be issues with front- or back-focusing, just like when using the optical viewfinder.
An alternative to the standard Live View mode is Focus Check Live View mode, which derives its image from the main sensor. Unlike earlier Sony DSLRs, this now allows use of either phase detection or contrast detection autofocus, rather than being limited solely to manual focusing. This mode hence now operates in much the same manner as the live view functionality of most competing DSLRs, as described previously -- and with all the mirror flipping that implies, when using phase detection AF. The preview image in this mode can be magnified by 7.5x or 15x for critical manual focusing, and unlike the standard Live View mode, frame coverage is 100%.
Both standard and Focus Check LV modes offer an advantage over shooting with the optical viewfinder when using the Wide area autofocus mode. Unlike the optical viewfinder, which simply indicates the location of all AF points at all times, the live view modes show which individual phase detection AF points achieved a focus lock, while the shutter button is half-pressed. This is indicated with a green highlight for these AF points, and is a great way to quickly confirm that the camera focused on the subject of your choice.
A depth-of-field preview button can be found adjacent to the grip, at the base of the lens mount. When held in, the A580 stops down its aperture to the selected value, allowing preview of the depth of field available in the scene. Depth of field preview is only available when using the optical viewfinder, or in Focus Check LV mode, but not in the standard live view mode. As with any SLR, the view through the optical viewfinder will dim while the aperture is stopped down. In Focus Check LV mode, though, the A580 adjusts preview sensitivity to attempt to show the image with correct brightness, making it easier to gauge depth of field with small apertures (but perhaps making the preview image grainy in low light conditions).
Sony A580 AF Assist
The Sony A580 uses its built-in flash head as a very bright AF-assist light for better focusing in dim lighting. This has the advantage that the light from the flash is very bright, but the downside is that you can only get AF assist when the flash head is raised. This is a real limitation for available-light photography, as the camera can expose at light levels well below those it can focus at. (Although its low-light focusing ability is much better than average.) If the camera is fixed on a tripod, you can work around this limitation, but it's somewhat awkward. With the flash head up, you must half-press the shutter button to make the camera focus, then switch the focus mode to manual focus, being careful not to touch the focus ring on the lens. Stow the flash head, and you can then take your picture. (But don't forget to switch back to AF mode for the rest of your shooting!)
Sony A580 Anti-Shake
The Sony A580 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 A580 to counteract camera movement with movements of the image sensor, rather than the more common approach of moving an optical element inside the lens.
Sony claims that the SteadyShot Inside anti-shake system in the A580 provides a 2.5 to 4-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 1/8 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.
When SteadyShot Inside is activated, the SteadyShot scale on the right side of the viewfinder display indicates the degree of stabilization. A downside to Sony's body-based SteadyShot approach is that while you can see the results of stabilization on competing lens-based designs, you have only this scale to tell you how the A580's SteadyShot mechanism is doing, at least while using the optical viewfinder. When using live view, the result of the Steadyshot system is shown in the live view feed, just as it would be with a lens-based system. The upside, though, is that the SteadyShot scale does give you a very good idea of how hard the SteadyShot mechanism is working, so you can choose a moment when the camera is moving less to snap the shutter, thus maximizing your chances for a sharp image.
Sony A580 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 anti-dust vibrations to automatically shake the sensor with the anti-shake mechanism each time the camera is shut off. There is also a manual cleaning mode, where the camera first triggers a longer burst of sensor shift shaking, then lifts the mirror and opens the shutter, allowing access to the sensor for use with a blower or other cleaning device. 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. Copper Hill Images is an advertiser of ours, but we'd recommend their wet/dry cleaning system even if they weren't (it's what we use in our own lab): See the Copper Hill website for details.
Lens Test Results
Good performance with the 18-55mm kit lens.
|18mm @ f/8||55mm @ f/8|
The Sony Alpha DSLR-A580 is available bundled with the Sony 18-55mm f/3.5-5.6 DT SAM lens, with a 35mm equivalent focal range of about 27-83mm. Results were good at 18mm, with strong detail across most of the frame and only minor softness in the corners (at f/8). Coma distortion in the trees was low, though a small to moderate amount of chromatic aberration was visible along high contrast elements near the edges of the image. Results were also good at the 55mm setting, with very good sharpness across the frame and minimal chromatic aberration in the highest contrast areas.
About average-size macro area with the kit lens, good flash performance.
|Macro with18-55mm kit lens
|Macro with Flash
As with zoom performance, the Sony A580's macro performance will depend entirely on the lens in use. With the 18-55mm kit lens set to 55mm, the DSLR-A580 captured a minimum area measuring 2.34 x 1.55 inches (59 x 39 millimeters), which is about average for an SLR kit lens. The shot with ambient light only (left) was underexposed, but resolution was quite good in the center despite appearing slightly soft, though there was some strong blurring in the corners. (Most lenses have some softening in the corners at macro distances.) The A580's flash throttles down pretty well for the macro area, and overall exposure is actually more even and much brighter.
Strong distortion at 18mm, though virtually none at 55mm.
|Strong barrel distortion at 18mm, ~1.0 percent|
|Less than a pixel of distortion at 55mm|
The Sony A580's 18-55mm kit lens produced higher than average barrel distortion at wide-angle, at about 1.0 percent, which is quite noticeable in some shots. At the telephoto end, there's not even a full pixel of distortion. 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
Moderate chromatic aberration at wide-angle; lower levels at full telephoto. The lens produced some soft corners at maximum aperture, especially at wide-angle.
|[email protected]/3.5: Upper right
C.A.: Moderate and bright
Softness: Strong blurring
|[email protected]/3.5: Center
|[email protected]/5.6: Lower right
C.A.: Moderate but dull
Softness: Noticeable blurring
|[email protected]/5.6: Center
C.A.: Very low
Softness: Slightly soft
Chromatic Aberration. Chromatic aberration in the corners with the Sony Alpha DSLR-A580's 18-55mm kit lens at wide-angle (18mm) is moderate in terms of the number of pixels, but those pixels are fairly bright. At full telephoto (55mm), C.A. is low to moderate but dull, so it's not as noticeable.
Corner Softness. The Alpha A580's 18-55mm kit lens produced very soft corners in a few shots at maximum aperture. At full wide-angle, the right-side corners were noticeably softer than the left, with the upper right corner softest overall, though noticeable blurring was also present in the other corners. Softness extended far into the frame from the right, though the left side was only soft in the extreme corners. The center of the image was sharp with good contrast. At full telephoto, the corners were slightly soft with lower contrast than wide-angle, though sharpness and contrast at the center were a hint lower as well. A slightly below average performance overall for a kit lens here. (Note that the lens was "wide-open" for these shots, and corner sharpness generally improves when a lens is "stopped-down" a couple of f-stops below full aperture.)
The Sony A580 doesn't appear to be applying any chromatic aberration in its JPEGs, as uncorrected RAW files show similar amounts.
The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Sony Alpha DSLR-A580 Photo Gallery .
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