Sony A55 Exposure
Sony Alpha A55 Exposure Options
The Sony A55 offers much the same exposure options you'd find in a traditional SLR camera, plus a few Sony-specific options. Available exposure modes include Program AE, Manual, Aperture Priority, and Shutter Priority modes, with shutter speeds from 1/4,000 to 30 seconds, as well as a Bulb setting for longer exposures. The x-sync speed for flash photography is 1/160 second. A fully automatic mode called Auto+ enables Scene Detection, and places the camera in control of almost all functions, to try to deliver optimum results under a wide range of conditions. Basic options such as exposure compensation aren't available to the photographer in this mode, and the A55 can even automatically enable multiple-exposure modes that capture a burst of images. The Sony A55 also offers a number of Scene modes, a Sweep Panorama mode, and a Multi Frame NR mode which merges multiple images into a single exposure with reduced noise. See the Modes and Menus page for more details.
The A55 offers an optional live histogram function in all operating modes except Sweep Panorama. Located near the bottom right corner of the LCD panel, it's rather small, and offers only a luminance readout rather than a full RGBY histogram, but it's still very useful for ensuring your exposures are correct. Another feature that's rather more common, but still very welcome, is the exposure display visible near the bottom right of the LCD when the camera is in Manual exposure mode. This shows the amount the camera thinks an image will be over- or underexposed within a range of +/-2.0EV, based on the settings you have selected, to help you find the best exposure for the subject. (Beyond the 2.0EV range, arrows on either end of the scale blink to emphasise that the metering system's limit has been reached.) Together, the live histogram and exposure display make it relatively easy to get suitable exposures even when shooting manually.
Sony A55 Face Detection
The Sony A55 includes Face Detection capability, capable of locating up to eight faces in the scene simultaneously. This information is taken into account when determining several exposure variables -- focus, exposure, flash and white balance. The A55 doesn't go as far as some cameras that try to recognize specific individuals, nor is it able to differentiate between adult and child faces. It does, however, includes a related feature that is now pretty common in point-and-shoot cameras, but relatively unknown in large-sensor cameras. Dubbed "Smile Shutter", this allows the A55 to automatically trigger the shutter, capturing photographs by itself when a smiling face is detected within the image frame. The A55's implementation is perhaps best suited to portraits of individuals, since the shutter is tripped when only one face within a group is smiling. There's a three-step control over the degree to which a subject must smile before the shutter is tripped. and when Smile Shutter is enabled, the A55 also provides a graph at the left of the screen that indicates how close a particular expression has come to passing the required threshold for the shutter to be tripped. In our testing we found the feature a little hit-and-miss, however, consistently spiking to the top of the scale and tripping the shutter for some individuals with barely the slightest smile, even when set to require a big smile.
Sony A55 ISO Range
ISO sensitivity ranges from 100 to 12,800, a wider range than that offered by many recent traditional SLRs. The ISO sensitivity is adjusted through the Function menu, or by pressing the ISO (Down Arrow) button on the four-way controller, and adjustments can be made in one-stop increments.
In all but Manual mode, an Auto ISO mode is available. The function is limited to a maximum of ISO 1,600 in most operating modes, although the Hand-held Twilight mode will allow Auto ISO to range as high as ISO 6,400 equivalent if needed.
In addition, the Sony A55 offers a Multi-Frame NR mode, which couples multiple shots into a single output image, in a similar manner to the Hand-held Twilight mode, but allows direct control over ISO sensitivity. When using Multi-Frame NR, the maximum ISO sensitivity limit is expanded to ISO 25,600 equivalent.
Sony A55 Noise Reduction
The Sony A55 gives you only two choices for High ISO noise reduction, neither of which allows the function to be completely disabled. The default is to leave High ISO NR entirely in the camera's control, but if the maximum image detail is desired (or you prefer to do your noise filtering in post processing), a "Weak" option is also available in all except Auto, Auto+, Sweep Panorama, or Scene modes. The Auto option cannot be selected in continuous shooting or bracketed image bursts.
A separate Long Shutter noise reduction On / Off setting is available for dark frame subtraction when shooting exposures of one second or longer. If enabled, this approximately doubles the exposure time for each shot, allowing the second dark frame exposure to be captured with the shutter closed. Long Exposure NR can't be disabled in Auto+, Auto, or Scene modes, and cannot be enabled for Multi-Frame NR, Sweep Panorama, Hand-Held Twilight, Continuous / Advance Priority Continuous, or Bracketed shooting.
Sony A55 White Balance Options
White balance modes on the Sony A55 include Auto, Daylight, Shade, Cloudy, Incandescent, Fluorescent, and Flash. A direct Kelvin temperature setting is also available, ranging from 2,500K to 9,900K, as is a Custom white balance setting, for setting white balance from a white or grey card. The A55's popup flash strobe can be used when determining a custom white balance, and unusually, the camera also provides a Kelvin readout of the measured color temperature -- a great feature which lets you dial the temperature in directly if you're shooting in familiar conditions. The effect of changes in white balance settings is shown in real-time, on the LCD monitor or EVF.
In all of the preset white balance modes, you can fine-tune the color by pressing the left / right arrow keys on the four-way controller while in the White Balance menu. Blue / red adjustment within a range of -3 to +3 arbitrary units for all but the fluorescent mode, which offers only a -1 to +2 unit range. In Kelvin white balance mode, there's also a color filter function which offers a magenta - green filter within a fairly wide range of -9 to +9 arbitrary units.
Custom white balance is set by selecting Custom Setup from the white balance menu, and pointing the camera at a neutral white or grey card under the lighting you'll be shooting in, filling a frame in the center of the display with the reference target, then pressing the Shutter button.
In addition, the Sony A55 can bracket white balance using the White Balance Bracketing (BRK WB) option in the Drive Mode menu. For each shutter release, the A55 records three separate image files, varying only the white balance between each image. Two step sizes are available -- 10 mireds when using the BRK WB Lo setting, and 20 mired steps with the BRK WB Hi setting.
Sony A55 Metering Options
The Sony Alpha A55 offers three metering modes, selected via the Metering Mode option in the Function menu: Multi-pattern, Center-Weighted, and Spot. All three modes operate on data from the camera's CMOS image sensor. The default Multi-segment metering mode divides the image into 1,200 segments, and compares these to determine exposure. Center-Weighted gives precedence to the center of the image while reading the whole frame. Spot metering is useful for high-contrast subjects, as it bases the exposure reading on the very center of the image, letting you set the exposure based on a small portion of your subject. When the camera is operating in Auto+, Auto, or Scene modes, the metering mode is fixed to Multi-pattern, and cannot be changed.
By default, you can lock an exposure reading separately from autofocus lock by pressing and holding the AEL button. Alternatively, the AEL button behaviour can be changed so that pressing and releasing the button will set and release the autoexposure lock on subsequent presses.
Sony A55 Exposure Compensation & Bracketing
The Sony A55's Exposure Compensation adjustment increases or reduces the overall exposure from -2 to +2 exposure values (EV) in one-third stop increments, and like White Balance, the effect of Exposure Compensation is simulated on the preview. In addition, the A55 offers -2 to +2 EV of flash exposure compensation, in 1/3 EV increments, set through the Function menu. A Continuous Bracketing feature captures multiple shots with different exposures. See the Drive Mode section on Continuous Bracketing below for more details.
Sony A55 DRO / HDR
The Sony A55 offers two different functions aimed at handling high-contrast scenes, each functioning in a rather different manner. The Dynamic Range Optimization (DRO) function adjusts the tone curve of captured images, bringing out shadow detail without adversely affecting highlights. As well as an Auto DRO mode, there are also five different levels of DRO available. Alternatively, Sony has included a high dynamic range (HDR) mode, which captures three separate images with varied exposures, and then combines the images in-camera, creating a single image with significantly increased dynamic range. The A55 can either automatically select the exposure variation, or a value can be selected manually in 1EV steps within a range of 1EV to 6EV.
The DRO and HDR modes can't be used together, and each brings its own set of advantages and disadvantages. Since DRO only works from a single shot, it must operate entirely within the dynamic range available from the image sensor, where the HDR mode is able to capture a significantly greater dynamic range than is possible in one shot. Since DRO is effectively amplifying the signal in shadow areas of the image, it also brings increased noise (or increased noise reduction) in the shadows. HDR mode, meanwhile, is suitable only for relatively static subjects, given that it requires multiple exposures. Thanks to microalignment capability, Sony's HDR mode is at least able to deal with the slight changes in framing caused by shooting handheld, but subject motion or camera shake will likely cause unacceptable artifacts in HDR images.
Both DRO and HDR can be disabled altogether if desired, although the default on the A55 is for DRO Auto mode to be left enabled.
Sony A55 Hand-held Twilight
Another function which the Sony A55 has inherited from the company's point-and-shoot camera line is its Hand-held Twilight mode, which is accessed from the Scene (SCN) position on the Mode dial. Hand-held Twilight mode shoots a burst of six images with a single press of the shutter button, using as high sensitivity as is necessary to offer hand-holdable shutter speeds. The A55 then combines all six source images into one image with reduced noise in static areas, as compared to a single shot taken with the same exposure settings. Cleverly, Hand-held Twilight mode is able to deal with moving subjects, by making the assumption that the first frame includes your intended subject. Areas of subsequent images which match up with the first image are factored into the final result, but areas that don't match -- either due to subject or camera motion -- aren't used in creating the final image. This does, however, mean that the moving subject doesn't benefit from the same degree of noise reduction as the rest of the image.
The Sony A55's implementation of Hand-held Twilight does have one important difference from the similar mode found on its point-and-shoot siblings. Where the existing cameras have been able to use an electronic shutter to capture the source images, the A55 must instead rely on its physical shutter. The act of firing the A55's shutter is surprisingly loud, given that there's no reflex mirror entering into the equation -- we've seen some DSLRs issuing similar noise levels (or possibly even a little less). The net result is that with six frames captured in a rapid burst, the A55's Anti-Motion Blur mode can have bystanders turning around in expectation of seeing a paparazzo in their midst. ;-)
Sony A55 Multi-Frame NR
Another function that's closely related to Hand-held Twilight is Sony's Multi-Frame NR mode. A new addition for Sony's SLT-series cameras, Multi-Frame NR has several important differences. Most significantly, it functions in the A55's Program, Aperture- or Shutter-Priority, and Manual modes. In all but Manual mode, it offers the ability to let the camera choose the sensitivity automatically, but unlike Hand-held Twilight it also allows manual selection of ISO sensitivity (and indeed, for Manual exposure shooting, that's the only option given.) One further difference of note is that in Multi-frame NR mode, the maximum ISO sensitivity limit of the Sony A55 is raised from its standard ISO 12,800 equivalent, to an impressively high 25,600 equivalent.
Sony A55 Sweep Panorama
The final mode inherited from Sony's Cyber-shot point-and-shoot lineup is the A55's Sweep Panorama function, with which it can automatically capture a burst of images, and stitch them into a single panoramic image in-camera. Both 2D and 3D modes are offered, with the latter cleverly comparing the relative positions of subjects as they pass the left and right sides of the lens, and using this information to create a 3D image consisting of separate 2D views, stored in a Multi Picture Object file.
Again, since there's no electronic shutter to rely on, the focal plane shutter noise means you won't be catching anybody by surprise, That said, the feature functions pretty well if you've a reasonably steady hand, and your subject matter isn't too close to the camera. If your subject matter is too close to the camera, or your panning isn't smooth and straight, the seams between separate images can become fairly noticeable. Focus and exposure are locked from the first frame of the panorama, so you'll want to pick your starting point carefully. From there, you can pan left, right, up, or down, simply sweeping the camera across your subject matter after pressing the shutter button.
Two panorama sizes are available -- standard, or wide. Standard horizontal panoramas are limited to 15 megapixels, and vertical panoramas to 8.4 megapixels. In Wide mode, horizontal panoramas are 23 megapixels, and vertical panoramas are 12 megapixels. For 3D mode, only horizontal panoramas are possible, with the standard size providing 5.3 megapixel resolution, and the wide size offering 7.7 megapixels. There's also a 1,920 x 1,080 pixel mode designed to match the resolution of a Full HD display, available only for 3D panoramas.
A darkened mask over the left third of the LCD display shows an area of the frame that won't be included in the final output image, and an on-screen message warns you if the Alpha A55 wasn't able to track your panning, prompting you to recapture the panorama. (Depending on how much was captured, the A55 sometimes retains a partial panorama with the uncaptured portion of the image left as a flat grey.)
Sony A55 Drive Modes
The Sony A55 offers a variety of shooting modes through the Drive Mode option under the Function menu, which can also be accessed by pressing the left-arrow button in all shooting modes except Continuous Advance Priority, Sweep Panorama, and Hand-held Twilight modes. Drive options vary depending on the shooting mode, but include Single Shot Advance, two Continuous Advance modes, two Self Timer modes, Continuous Bracket, White Balance Bracket, and Remote Commander. Single-shot, as you'd expect, captures a single image with each press of the shutter button. Continuous Advance captures images at either six frames per second in Hi mode, or three frames per second in Lo mode, while the shutter button is held down. As many as 19 RAW or 28 Large / Fine JPEG shots can be captured in a burst, adjusting focus and exposure between shots as necessary. The Self-timer modes offers a choice of either two or ten second timers. Continuous Bracket mode lets you take a sequence of three shots with either 0.3 EV or 0.7 EV exposure variation steps, with the sequence order being to shoot the metered exposure first, followed by the underexposed and overexposed frames. White Balance Bracket captures three images with varied white balance settings, as describe in the white balance section of this page. Finally, Remote Commander mode configures the A55 to capture images as directed by the optional RMT-DSLR1 wireless remote control, which communicates with the camera via an infrared receiver located in the top of the hand grip.
The Sony A55 also offers a separate Continuous Advance Priority mode, accessed from its own position on the Mode dial. When enabled, this boosts the frame rate significantly to a whopping ten frames per second, and allows both autofocus and autoexposure to continue to operate between frames. There's an important proviso to note if using Continuous Autofocus, though. To allow sufficient light to reach the camera's phase detection autofocus sensor without the need to adjust the lens aperture between frames, the Continuous Advance Priority mode locks the aperture at or near its open position, reducing the available depth of field. The only way to avoid this requirement is to use either single autofocus, or manual focus. With single autofocus, the focus point is locked from the first frame.
Sony A55 Creative Styles
The Creative Style option on the Function menu allows photographers to set the A55's color mode. Six preset options are available -- Standard, Vivid, Portrait, Landscape, Sunset, and B/W. For all six choices, Contrast and Sharpness levels may be adjusted in seven steps. In addition, all but the black and white mode offer seven-step control over saturation. A separate Color Space option under Screen 2 of the Record menu lets you choose between sRGB and AdobeRGB color spaces, with sRGB being best for viewing images on a computer, and Adobe RGB the best choice for printing images.
Sony A55V Geotagging
Finally, the Sony A55V allows geotagging of images and movies at the time of capture. This allows them to be tagged with information regarding capture location, including latitude, longitude, altitude, receiver speed and direction, and the GPS time stamp. Movies are only tagged with information regarding the location at the start of the clip. Accuracy will vary depending on the number of satellites in view at a particular time and location. The initial GPS lock can take several minutes to achieve, if the camera hasn't been used recently, although again this can depend on environmental conditions, as well as the number and position of satellites in view. It's possible to reduce this time by uploading GPS-assist data to the A55V body using Sony's provided Picture Motion Browser software, which can greatly reduce the length of time required to obtain a GPS lock. This process has to be repeated roughly once per month, as the assist data is only good for so long.
Note that all this information pertains only to the A55V model, with the standard Sony A55 model lacking a GPS receiver, and so not including this functionality. In the US market, the only available model is technically the Sony A55V, although it will likely be referred to by many users and photographers as the Sony A55. In overseas markets where both variants are available, though, you'll want to pay attention to which specific model you're considering.
The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Sony Alpha SLT-A55V Photo Gallery .
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Note: For details, test results, and analysis of the many tests done with this camera, please click on the tabs at the beginning of the review or below.
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