Sony A58 Exposure
Sony A58 Image Quality
Saturation & Hue Accuracy
Typical saturation levels and hue accuracy.
|In the diagram above, the squares show the original color, and the circles show the color that the camera captured. More saturated colors are located toward the periphery of the graph. Hue changes as you travel around the center. Thus, hue-accurate, highly saturated colors appear as lines radiating from the center. Mouse over the links to compare ISOs and click on links for larger images.|
Saturation. The Sony A58's overall default color saturation is oversaturated by 9.6% at base ISO, which is about average these days. Saturation remains fairly consistent across the ISO range, except at ISO 6400 where it dips to 102.6%. Reds and dark blues are boosted the most, but not as much as we often see. Most other colors are pushed just a bit, though yellow and cyan are slightly undersaturated which is quite common. Overall, saturation levels are quite pleasing to our eyes, and you can of course tweak them more to your liking. Most consumer digital cameras produce color that's more highly saturated (more intense) than found in the original subjects. This is simply because most people like their color a bit brighter than life.
Skin tones. The Sony A58 does fairly well with Caucasian skin tones. Brighter flesh tones have a healthy pinkish tint, though darker areas are nudged toward orange. Still, pretty good results here. Where oversaturation is most problematic is on Caucasian skin tones, as it's very easy for these "memory colors" to be seen as too bright, too pink, too yellow, etc.
Hue. Like many cameras, the Sony A58 shifts cyan toward blue, red toward orange, orange toward yellow and yellow toward green, but shifts are relatively minor. (The cyan to blue shift is very common among the digital cameras we test; we think it's a deliberate choice by camera engineers to produce better-looking sky colors.) With an average "delta-C" color error of 5.17 after correction for saturation at base ISO, overall hue accuracy is about average, with accuracy only moderately lower at higher ISOs. Hue is "what color" the color is.
The Sony A58 has a total of seven saturation settings available, three above and three below the default saturation. This covers a pretty wide range of saturation levels. Saturation also had almost no effect on contrast, which is how it should work.
|Saturation Adjustment Examples|
The table above shows results with five of the seven saturation settings, including the default and the two extremes. Click on any thumbnail above, then click again to see the full-sized image.
|See full set of test images with explanations
See thumbnails of all test and gallery images
Exposure and White Balance
Indoors, incandescent lighting
Slightly warm casts with Auto and Incandescent, good with Manual, and a touch cool with Kelvin white balance settings. Average exposure compensation required.
|Auto White Balance
|Incandescent White Balance
|Manual White Balance
Indoors, under normal incandescent lighting, color balance is a bit warm and orange with the Auto white balance setting, though results here are slightly better than average. Results with the Incandescent setting are a bit better but still somewhat warm and orange/yellow. The Manual setting is quite accurate, just slightly on the cool side. The 2,600 Kelvin setting which should match the color temperature of our lights is too cool and bluish. The Sony A58 required +0.3 EV positive exposure compensation here, about average for this shot, though images are just a touch bright. (Our test lighting for this shot is a mixture of 60 and 100 watt household incandescent bulbs, a pretty yellow light source, but a very common one in typical home settings here in the U.S.)
Very good results under harsh lighting, with good handling of contrast, color, and exposure.
|Auto White Balance,
|Auto White Balance,
Outdoors, the Sony A58 performed very well. No exposure compensation was required to keep the mannequin's face reasonably bright in our "Sunlit" Portrait shot, which is much better than average among the cameras we've tested. (Most cameras require about +0.7 EV here.) Contrast is a little high as you might expect under such harsh lighting, but the camera does a good job of holding onto detail in both the shadows and bright highlights, even without the help of DRO (see below). Both Auto and Manual while balance produced decent skintones, with lighter tones slightly pinkish while darker ones slightly warm, with a slight orange tint. Default exposure is quite good for our Far-field shot as well, just a touch underexposed but with very few highlights blown, again with DRO disabled. There are quite a few dark shadows in the trees, however only very dark shadows are noisy and posterized, but that's not usually an issue as we're talking *very* dark shadows. The Far-field shot with Auto white balance has very good color, just a touch on the cool side. Overall, a very good performance in harsh lighting, especially considering DRO was off for these shots.
Very high resolution, ~2,500 lines of strong detail from both JPEGs and RAW files.
|Strong detail to
~2,500 lines horizontal
|Strong detail to
~2,500 lines vertical
|Strong detail to
~2,500 lines horizontal
ACR converted RAW
|Strong detail to
~2,500 lines vertical
ACR converted RAW
In-camera JPEGs of our laboratory resolution chart reveal sharp, distinct line patterns down to about 2,500 lines per picture height in both the horizontal and vertical directions. Some may argue for higher numbers, but aliasing and sharpening artifacts start to interfere at this resolution. Complete extinction of the pattern doesn't occur until about 3,200 lines. Some color moiré is evident in JPEGs, though that's not uncommon. Adobe Camera Raw wasn't really able to extract more lines of resolution here from a matching RAW file, and it generated stronger color moiré, so the Sony A58 does a good job holding on to high contrast detail at base ISO in its JPEGs. Use these numbers to compare with other cameras of similar resolution, or use them to see just what higher resolution can mean in terms of potential detail.
Sharpness & Detail
Good default sharpness, though fine detail is a touch soft. Mild to moderate noise suppression visible in the shadows and areas of low contrast.
|Good definition of high-contrast
elements with some minor sharpening
artifacts. Fine detail is just a touch soft.
|Subtle detail: Hair
Noise suppression tends to blur
detail in areas of subtle contrast.
Sharpness. The Sony A58 captures sharp, detailed images overall, though results are a touch soft at default settings, despite using a very sharp Carl Zeiss 24-70mm F/2.8 SSM lens at f/8 for the shot above left. There are some minor edge enhancement artifacts seen around high-contrast elements such as sharpening halos around the larger tree branches and pine cones, but they're not excessive and quite normal. Fine detail such as the smaller branches and pine needles show very little edge enhancement, but appear a little mushy due to noise reduction. Edge enhancement creates the illusion of sharpness by enhancing colors and tones right at the edge of a rapid transition in color or tone.
Detail. The crop above right shows mild to moderate noise suppression in the darker areas of the model's hair. A number of low-contrast strands are smudged together, though higher contrast strands are still distinct. We saw similar results with fine detail in the pine needles being flattened a bit. Still, pretty good results here, especially for a high-resolution APS-C sensor. We did however notice some demosaicing errors in the form of blue or green pixels that look like chroma noise in the hair, as well as hints of the "jaggies," a type of aliasing artifact. This implies the A58 has a fairly weak optical low-pass filter, but you have to look pretty closely to spot them. Noise-suppression systems in digital cameras tend to flatten-out detail in areas of subtle contrast. The effects can often be seen in shots of human hair, where the individual strands are lost and an almost "watercolor" look appears.
RAW vs In-Camera JPEGs
As noted above, the Sony A58 produces in-camera JPEGs with very good detail, though fine, low-contrast detail is a touch soft. Quite a bit more detail can often be obtained from carefully processing RAW files with a good converter, as can be seen below.
In the table above, mousing over a link at the bottom will load the corresponding crop in the area above, and clicking on the link will load the full resolution image. Examples include (from left to right): an in-camera Fine JPEG, the matching RAW file processed through Sony's bundled Image Data Converter software at default settings, and finally the same RAW file converted with Adobe Camera Raw 8.1, then sharpened in Photoshop using unsharp mask at 300% with radius 0.3.
As you can see, the Sony IDC version at default settings has somewhat better detail (and slightly different color) the in-camera JPEG, though sharpening artifacts are a little more prominent. The Adobe Camera Raw conversion shows better detail than both the in-camera JPEG and the IDC conversion, less obvious sharpening halos, but also reveals a bit more noise. You can always turn up the luminance noise reduction (default of zero was used here), or process the files in your favorite noise reduction program or plugin if you want cleaner images. Bottom line: as is usually the case, the Sony A58 rewards RAW shooters with improved detail (and much better control over the final image) when processed with a good converter.
ISO & Noise Performance
Very good noise versus detail performance up to ISO 1,600.
Default High ISO Noise Reduction
|ISO 100||ISO 200||ISO 400|
|ISO 800||ISO 1,600||ISO 3,200|
|ISO 6,400||ISO 12,800||ISO 16,000|
The Sony A58's JPEG images are very clean up to ISO 400, though as mentioned previously some very fine, mostly low-contrast detail is lost to noise reduction already at base ISO. There are demosaicing errors in the hair above the mannequin's forehead, though that's pretty common these days, especially with a sharp lens. Stronger noise reduction at ISO 800 removes much of the colored pixels with just a slight increase in smudging, though the aliasing artifacts mentioned earlier are still visible. ISO 1,600 is slightly softer though detail is still very good, and the aliasing artifacts have practically vanished. ISO 3,200 is noticeably softer with stronger smudging and more noticeable noise "grain", but detail is still pretty good for the sensitivity. Image quality goes down rapidly from there, though. ISO 6,400 still shows some fine detail, but 12,800 and especially 16,000 suffer from much stronger blurring and more noticeable luma noise accentuated by the camera's sharpening. Chroma noise is also stronger at these high ISOs, producing blotchy purple and yellow patches. Overall, though, these are very good results especially considering the A58's price point and resolution.
As always, see the Print Quality section below for maximum recommended print sizes at each ISO, as printed performance often doesn't correlate well to what's seen on-screen at 100%.
A note about focus for this shot: We shoot this image at f/4, usually using one of three very sharp reference lenses (70mm Sigma f/2.8 macro for most cameras, 60mm f/2.8 Nikkor macro for Nikon bodies without a drive motor, and Olympus Zuiko 50mm f/2.0 for Four Thirds and Micro Four Thirds bodies). To insure that the hair detail we use for making critical judgements about camera noise processing and detail rendering is in sharp focus at the relatively wide aperture we're shooting at, the focus target at the center of the scene is on a movable stand. This lets us compensate for front- or back-focus by different camera bodies, even those that lack micro-focus adjustments. This does mean, though, that the focus target itself may appear soft or slightly out of focus for bodies that front- or back-focused with the reference lens. We know this; if you click to view the full-size image for one of these shots and notice that the focus target is fuzzy, you don't need to email and tell us. :-) The focus target position will have been adjusted to insure that the rest of the scene is focused properly.
Extremes: Sunlit, dynamic range and low light tests
Very high resolution with very good highlight and shadow detail. Good low-light performance, capable of capturing bright images in near darkness, though AF struggled at lower light levels.
|0 EV||+0.3 EV||+0.7 EV|
Sunlight. The Sony A58 handled the deliberately harsh lighting in the test above very well. We preferred the default (0 EV) exposure here as the face is reasonably bright while almost no highlights were clipped in the white shirt. Some may prefer the +0.3 EV exposure for its brighter exposure in the face, though, while the +0.7 EV exposure is definitely too bright. It's really up to the photographer. Folks printing directly from the camera will likely want the +0.3 EV image, while people post processing will likely prefer the default exposure for its slightly better highlight retention. As mentioned previously, contrast is a little high, but highlight detail is very good at default exposure. There are some deep shadows however they contain good detail, though very deep shadows are posterized. However, that's not really an issue except perhaps for those trying to recover a severely underexposed image.
For best results, be sure to use fill flash in situations like the one shown above; it's better to shoot in the shade when possible. See below for results with Dynamic Range Optimization and High Dynamic Range features enabled.
Because digital cameras are more like slide film than negative film (in that they tend to have a more limited tonal range), we test them in the harshest situations to see how they handle scenes with bright highlights and dark shadows, as well as what kind of sensitivity they have in low light. The shot above is designed to mimic the very harsh, contrasty effect of direct noonday sunlight, a very tough challenge for most digital cameras. (You can read details of this test here. In actual shooting conditions, be sure to use fill flash in situations like the one shown here; it's better to shoot in open shade whenever possible.)
Dynamic Range Analysis
A key parameter in a digital camera is its Dynamic Range, the range of brightness that can be faithfully recorded. At the upper end of the tonal scale, dynamic range is dictated by the point at which the RGB data "saturates" at values of 255, 255, 255. At the lower end of the tonal scale, dynamic range is determined by the point at which there ceases to be any useful difference between adjacent tonal steps. Note the use of the qualifier "useful" in there: While it's tempting to evaluate dynamic range as the maximum number of tonal steps that can be discerned at all, that measure of dynamic range has very little relevance to real-world photography. What we care about as photographers is how much detail we can pull out of the shadows before image noise becomes too objectionable. This, of course, is a very subjective matter, and will vary with the application and even the subject matter in question. (Noise will be much more visible in subjects with large areas of flat tints and subtle shading than it would in subjects with strong, highly contrasting surface texture.)
What makes most sense then, is to specify useful dynamic range in terms of the point at which image noise reaches some agreed-upon threshold. To this end, Imatest computes a number of different dynamic range measurements, based on a variety of image noise thresholds. The noise thresholds are specified in terms of f-stops of equivalent luminance variation in the final image file, and dynamic range is computed for noise thresholds of 1.0 (low image quality), 0.5 (medium image quality), 0.25 (medium-high image quality) and 0.1 (high image quality). For most photographers and most applications, the noise thresholds of 0.5 and 0.25 f-stops are probably the most relevant to the production of acceptable-quality finished images, but many noise-sensitive shooters will insist on the 0.1 f-stop limit for their most critical work.
JPEG. The graph at right (click for a larger version) was generated using Imatest's dynamic range analysis for an in-camera Sony A58 JPEG file with a nominally-exposed density step target (Stouffer 4110). At the base ISO of 100 (the optimal ISO) with DRO and HDR settings turned off, the graph shows 11.4 f-stops of total dynamic range, with 7.99 f-stops at the "High" Quality level. Roll-off at the highlight end of the curve is gradual, and the low end extends fairly linearly, but the steps get rather spread out, indicative of a tendency of the deepest shadows to break up into discrete levels (posterization) if you try to brighten them too much. These are good results for in-camera JPEGs from a consumer model. Compared to the Nikon D3200 for example, the A58 scored slightly higher at the High Quality level (7.99 vs 7.65), but significantly lower in total dynamic range (11.4 vs 12.3 f-stops). Note though that this measurement has a margin of error of about 1/3 f-stop, so differences of less than 0.33 can be ignored.
RAW. The graph at right is from the same Stouffer 4110 stepchart image captured as a RAW (.ARW) file, processed with Adobe Camera Raw using the Auto setting, then manually tweaking from there. As can be seen, the score at the highest quality increased by over 1-1/3 stops from 7.99 to 9.37 f-stops compared to the in-camera JPEG, while total dynamic range also increased by a similar amount from 11.4 to 12.6. Again, these dynamic range scores are pretty good, but not quite as good as some leading competitors. Compared to the Nikon D3200, the A58 scored lower in total dynamic range (12.6 vs 13.3 f-stops), but slightly higher at the high quality level (9.37 vs 8.84 f-stops). It's worth noting here is that ACR's default noise reduction settings reduced overall noise somewhat (see the plot in the lower left-hand corner) relative to the levels in the in-camera JPEG, which would tend to boost the dynamic range numbers for the High Quality threshold. Also, the extreme highlight recovery being performed by ACR here would likely produce color errors in strong highlights of natural subjects.
We really like it when a camera gives us the ability to adjust contrast and saturation to our liking. It's even better when those adjustments cover a useful range, in steps small enough to allow for precise tweaks. Just as with its saturation adjustment, the Sony A58's contrast setting meets both challenges.
|Contrast set to lowest,
|Contrast set to lowest,
At its lowest contrast setting, the A58 does a really excellent job of toning down highlights and opening up shadows while maintaining natural-looking skin tones. Very good results here.
|Contrast Adjustment Examples|
The table above shows five of the seven contrast setting, including the default and two extremes. It's pretty hard to evaluate small differences in contrast on small thumbnails like these, so click on any thumbnail to go to the full-size image.
One very nice feature of Sony's contrast adjustment is that it has very little effect on color saturation. Contrast and saturation are actually fairly closely coupled, it's a good trick to be able to vary one with out the other changing as well. As usual, Sony did a good job here.
Outdoor Portrait DRO Comparison
Dynamic Range Optimization is Sony's name for their dynamic range enhancement technology. DRO divides the image into small areas, analyzes the range of brightness of each area, and adjusts the camera's image processing parameters accordingly to make the best use of the available dynamic range. DRO does not boost ISO like some systems, so increased noise is less of an issue, though existing noise may be more visible in raised shadows. Auto DRO is enabled by default on the Sony A58. You can also set the level manually, from 1 ("weak") to 5 ("strong"), or turn it off. As one would expect, DRO is only available for JPEG files.
The above thumbnails and histograms show the effects of the available levels of DRO on our "Sunlit" Portrait shot with no exposure compensation. Mouse over the links to load the associated thumbnail and histogram, and click on the links to visit the full resolution image. As you can see from the thumbnails and associated histograms, DRO boosts shadows and mid-tones without blowing additional highlights, yielding a more balance exposure. Auto DRO setting did a good job here, and the five manual levels give quite a bit of control over the effect.
Above, you can see the effect of DRO settings on our Far-field shot. The default Auto setting produced a very good exposure overall, despite the harsh lighting. Nice.
High Dynamic Range. The Sony A58's HDR mode takes three images in rapid succession, one nominally exposed , one underexposed, and one overexposed, then combines them into one high dynamic range JPEG automatically. Lighter areas from the underexposed image are combined with darker areas from the overexposed image to produce an image with compressed tonal range. The camera then saves a single composite image, as well as the nominally exposed image. The overlaid images are micro-aligned by the camera, but it can only correct for so much movement. If it can't micro-align successfully, an icon indicating HDR capture failed will appear. For best results, the subject should not move or blink, so it's not really intended for portraits. There is also a manual mode where you can select 1 EV ("weak") to 6 EV ("strong") difference in exposures.
Mouse over the links to load the associated thumbnail and histogram, and click on the links to visit the full resolution image. As you can see, the Auto setting did a decent job boosting shadows and mid-tones while reigning back highlights, however we prefer the lower manual settings for this subject. The higher the manual setting, the more highlights are toned-down and shadows opened up, but higher settings can produce flat and unnatural results with this scene. Still, it's nice that Sony provides six manual levels, giving quite a bit of control over the effect.
Above, you can see the effect of HDR settings on our Far-field shot. Watch out for ghosting and other artifacts caused by subject movement during the capture sequence, though, as you can see in the people and around the flag and leaves in some of the above shots.
Low Light. The Sony A58 was able to capture bright images down to the lowest light level we test at (1/16 fc) at all ISO settings. Noise is well controlled up to ISO 3,200, though as expected, at higher ISOs there are moderate to high amounts of fine luminance noise and some blotchy chroma noise. A few hot pixels can be seen particularly with long exposure noise reduction turned off (the right-most column), but nothing out of the ordinary. We didn't detect any significant banding (pattern noise), perhaps just a hint of horizontal banding at the highest ISO where it's not usual. Some heat blooming (reddish tint) emanating from the bottom of the frame can be seen at the highest ISOs and lower light levels, but that's not unusual either.
Auto white balance did a very good job here, producing a fairly neutral, just slightly cool color balance.
Note that the left-most column in the above table contains images shot at one foot-candle using Sony's Multi-frame NR feature. See below for more details.
The Sony A58's autofocus system was only able to focus on the subject down to between the 1/4 and 1/8 foot-candle light level unassisted with an f/2.8 lens in our tests, which isn't as good as most true DSLRs. The A58 was however able to focus in complete darkness with its built-in focus assist lamp enabled.
How bright is this? The one foot-candle light level that this test begins at roughly corresponds to the brightness of typical city street-lighting at night. Cameras performing well at that level should be able to snap good-looking photos of street-lit scenes.
NOTE: This low light test is conducted with a stationary subject, and the camera mounted on a sturdy tripod. Most digital cameras will fail miserably when faced with a moving subject in dim lighting. (For example, a child's ballet recital or a holiday pageant in a gymnasium.) Thanks to their phase-detect AF systems, digital SLRs (SLTs) like the Sony A58 tend to do much better than point & shoots, but you still shouldn't expect a quick autofocus lock with moving subjects. (A useful trick is to just prop the camera on a convenient surface, and use its self-timer to release the shutter. This avoids any jiggling from your finger pressing the shutter button, and can work quite well when you don't have a tripod handy.)
|Low Light Multi-frame NR|
|Default NR, 1/60s, ISO 12,800||Multi-frame NR, 1/60s, ISO 12,800|
Multi-frame Noise Reduction. This feature is similar to Sony's Hand-held Twilight mode which shoots a burst of six images with a single press of the shutter button and combines all six images into one composite image with reduced noise. But unlike Hand-held Twilight, Multi-frame NR gives you control over the ISO, aperture and shutter speed used, so you may still need to use a tripod depending on the exposure parameters you select. (We frankly don't see the value to this mode when using a tripod, as selecting a lower ISO and longer shutter speed will produce a cleaner image as well.) As you can see, the image captured with Multi-frame Noise Reduction (right) is cleaner than the standard image (left) despite both being shot at ISO 12,800. An added bonus is that ISO 25,600 equivalent is available with MF NR. As with HDR mode, though, static subjects are recommended.
Excellent 30 x 40 inch prints at ISO 100/200; a nice 11 x 14 at ISO 3200; and even prints a good 4 x 6 at its highest ISO of 16,000.
ISO 400 makes a very tight 24 x 36 inch print, with sharp detail, and wall display prints up to 30 x 40 inches.
ISO 800 yields a nice, crisp 16 x 20. The 20 x 30 inch print here is suitable for less critical applications where minor film-grain like noise is OK in some areas.
ISO 1,600 is capable of a good 13 x 19 inch print. There is minor noise now apparent in some shadowy areas, and a slight decrease in contrast in our target red swatch.
ISO 3,200 prints a good 11 x 14. There is now a fair amount of noise visible in some flat areas, but otherwise a nice print overall.
ISO 6,400 produces a nice 8 x 10 for this ISO. It is beginning to lose contrast detail in our tricky red swatch, as most cameras do here, but a very solid print.
ISO 12,800 prints a good 5 x 7, with colors still popping nicely. This is the same print size we rated as good at this ISO for the A58's acclaimed great uncle the RX1.
ISO 16,000 makes a good 4 x 6. This is significant because so many cameras we have reviewed lately do not yield a suitable 4 x 6 at their highest ISO.
We could say the Sony A58 does a very good job in the print quality department from JPEGs, but when you consider its body-only street price of somewhere under $600, it'd be fairer to say it does an excellent job. We don't take price or any other factors into consideration when evaluating prints, just how they look, but drawing a conclusion is another story. Simply put, if you are looking at stepping into your first DSLR, or if you need a solid back-up to your more advanced model, the A58 can be counted on in the JPEG image quality department across the ISO spectrum.
Testing hundreds of digital cameras, we've found that you can only tell just so much about a camera's image quality by viewing its images on-screen. Ultimately, there's no substitute for printing a lot of images and examining them closely. For this reason, we now routinely print sample images from the cameras we test on our Canon Pro9000 Mark II studio printer, and the Canon Pixma MP610 here in the office. (See the Canon Pixma Pro9000 Mark II review for details on that model.)
The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Sony Alpha SLT-A58 Photo Gallery .
Not sure which camera to buy? Let your eyes be the ultimate judge! Visit our Comparometer(tm) to compare images from the Sony Alpha SLT-A58 with those from other cameras you may be considering. The proof is in the pictures, so let your own eyes decide which you like best!
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