Sony Alpha SLT-A33
Sony A33 Image Quality
Saturation & Hue Accuracy
Very good overall accuracy and saturation, with only minor shifts in hue and intensity.
Skin tones. Here, when adjusted for the correct white balance, the Sony A33 did well, producing natural-looking skin tones. 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. The Sony A33 did push cyan toward blue, red toward orange, orange toward yellow and yellow toward green, but shifts were 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 only 4.53 after correction for saturation, overall hue accuracy was very good; much better than average. Hue is "what color" the color is.
The Sony A33 offers six preset "Creative Style" options. You can adjust contrast, saturation, and sharpness for any of the settings.
|Creative Style Options|
Mouse over the links above to see the effect of the presets on our Still Life target. Click on a link to load the full resolution image.
The Sony A33 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, about as wide a range as you're likely to find photographically relevant, apart from special effects that are arguably better achieved in software. The fine steps between settings mean you can program the camera to just the level of saturation you prefer, a feature we look for in cameras.
|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
Very warm cast with Auto, but good color with the Incandescent and Manual settings. About average amount of positive exposure compensation required.
|Auto White Balance
|Incandescent White Balance
|Manual White Balance
Indoors, under normal incandescent lighting, color balance was overly warm with the Auto white balance setting. Results with the Incandescent setting were quite good, just slightly warm. The Manual setting was very accurate, though some may prefer Incandescent because it conveys a touch more of the warmth of the original lighting. The 2,600 Kelvin setting which matches the color temperature of our lights resulted in a slightly cool, bluish image. The Sony A33 required +0.3 EV positive exposure compensation here, which is average for this shot. (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, detail, and exposure.
|Manual White Balance,
|Auto White Balance,
Outdoors, the Sony A33 performed well, requiring no exposure compensation to keep the model's face bright in our "Sunlit" Portrait shot. The average among the cameras we've tested is +0.7 EV, so the A33 performed better than average 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 deep shadows and bright highlights, without the help of DRO (DRO was off for these shots). Despite the apparent brightness, there are very few clipped highlights in the model's face and shirt, with most of the clipping occurring in specific color channels in the flowers. There weren't many lost shadows either. Only a few highlights were blown in the House shot at the default exposure as well, also a very good result. Color balance is good, though Auto white balance rendered the model's face a touch too cool. We preferred results from the Manual white balance setting. The Far-field House shot had very good color, also just a touch cool. Overall, very good performance.
Very high resolution, 1,900 ~ 2,100 lines of strong detail.
|Strong detail to
2,100 lines horizontal
|Strong detail to
1,900 lines vertical
In camera JPEGs of our laboratory resolution chart revealed sharp, distinct line patterns down to about 2,100 lines per picture height in the horizontal direction, and about 1,900 lines per picture height in the vertical direction. Complete extinction of the pattern didn't occur until about 2,600 to 2,800 lines. 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
Very good detail and sharpness, with some minor edge-enhancement on high-contrast subjects. Moderately low noise suppression visible in the shadows and areas of low contrast.
|Very good definition of high-contrast
elements with some visible
|Subtle detail: Hair
Noise suppression tends to blur
detail in areas of subtle contrast.
Sharpness. The Sony A33 captures fairly sharp, detailed images overall when using a sharp lens (the above left crop is from a shot taken with the very sharp Carl Zeiss Vario-Sonnar T* 24-70mm F2.8 lens), though some edge enhancement artifacts are visible on high-contrast subjects such as the tree branches, roof and trim in the crop above left. Fine detail such as the smaller branches and pine needles show very little edge enhancement. The A33 offers seven levels of sharpening though, so you can always tweak JPEG output to your taste. 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 moderately low noise suppression in the darkest areas of the model's hair. Some individual strands are smudged together, though quite a few strands are still visible despite the low contrast subject. Overall, very good results here for a 14-megapixel APS-C sensor. 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 A33 produces fairly sharp, detailed in-camera JPEGs. However, quite a bit more detail can often be obtained from carefully processing RAW files with a good RAW converter.
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, RAW file processed through Sony's Image Data Converter SR version 3.2 software at default settings, another processed with IDC's sharpening turned up to +100, and finally one converted with Adobe Camera RAW 6.2, sharpened in Photoshop. For the Sony A33's images, I found best results with strong but tight 300% unsharp masking with an 0.3 pixel radius.
As you can see, the Sony IDC version at default settings is somewhat softer than the in-camera JPEG. (Color rendering is also slightly different.) Increasing the sharpness helped, but the resulting image doesn't really show any additional detail. There is also an odd green coloration along some of the white trim on the house that's not present in the camera JPEG, so it's possible IDC still needs some work to properly support the Sony A33's ARW files. On the other hand, the Adobe Camera RAW version sharpened in Photoshop reveals quite a bit more fine detail.
ISO & Noise Performance
Very good noise performance for a 14-megapixel APS-C sensor, with excellent results up to ISO 800.
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|
The Sony A33's images are quite clean at ISO 100 and 200, and ISO 400 is almost as good. Some noise "grain" is noticeable at ISO 800, and there's a bit of chroma noise in the shadows, but the camera doesn't smudge away as much fine detail as most others at this ISO. There's some stronger smudging of fine detail at ISO 1,600, but the A33 still does better than most at this ISO for its resolution. At ISO 3,200, fine detail suffers from more aggressive noise reduction, but there is still some detail left, though chroma noise is starting to become an issue in the shadows. Detail takes larger hit at ISO 6,400 and especially 12,800. There's also quite a bit of chroma noise in the form of purple and yellow blotching, especially at ISO 12,800. Overall though, these are very good results, but not quite as good as those from the Sony NEX-3 and NEX-5 which likely share the same or very similar sensor. As always, see the Print Quality section below for maximum recommended print sizes at each ISO.
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.
High ISO NR = Weak
High ISO NR = Auto
Noise Reduction Oddity. The "Weak" high ISO NR setting smudges the red leave pattern in our Still Life target setting more than the "Auto" setting at higher ISOs. The Auto setting does reduce chroma noise compared to the Weak setting though (lower crops). We saw similar behavior with previous Sony models such as the NEX-5/3 and A550/A500.
Extremes: Sunlit and low light tests
Very high resolution with excellent highlight and shadow detail. Very good low-light performance, capable of capturing bright images in near darkness. Special modes make it possible to capture low-light images without a tripod.
|0 EV||+0.3 EV||+0.7 EV|
Sunlight. The Sony A33 handled the deliberately harsh lighting in the test above very well. Though contrast is a little high, shadow and highlight detail are both very good. The camera's contrast adjustment also did a good job of decreasing overall contrast without producing strong color variations; see the section below. The default exposure (0 EV) did the best job here, as the model's face was reasonably well exposed without blowing as many highlights as the +0.3 and +0.7 EV settings. Note that these shots were captured with the Sony A33's DRO (Dynamic Range Optimizer) control set to Off, so the camera's dynamic range is pretty good even without the aid of DRO. Still, 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 DRO results.
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.)
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 A33's contrast setting meets both challenges.
|Contrast set to lowest,
|Contrast set to lowest,
At its lowest contrast setting, the A33 did a really excellent job of preserving highlight detail, maintaining natural-looking skin tones, and holding nice detail in the shadows. The Sony A33 captures good color outdoors, though just a touch on the cool side. Overall, very good results here, especially when the contrast setting is tweaked. (This is a really tough shot; the Sony does a much better than average job handling it.)
|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. Sony did a good job here.
|Outdoor Portrait DRO Examples|
|DRO Off||DRO Auto||DRO Level 1||DRO Level 5|
(Levels adjusted equally in Photoshop on the right-hand side to show noise)
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. The Sony A33 enables Auto DRO by default. You can also set the level manually, from 1 ("weak") to 5 ("strong"). As one would expect, DRO is only available for JPEGs.
The above images and crops show the effects of DRO disabled, set to Auto (the default), Level 1 ("weak") and Level 5 ("strong") for our "Sunlit" Portrait shot. As you can from the crops, Auto DRO had very little effect on the highlights in this shot, as the images are virtually the same when it comes to highlights. This is because very few highlights were lost in the first place. (Despite the apparent brightness, almost no highlights were clipped in the white shirt.) The bulk of the difference between different levels of DRO is found in the shadow areas. The stronger the level, the more boost is applied to the shadows. Along with that boost is an increase in shadow noise, though noise is not as much of an issue as we expected for a 14-megapixel subframe sensor.
|Far Field DRO Auto Example|
|DRO Off, 0 EV||DRO Auto, 0 EV|
Here's an example of Auto DRO at work with our Far-field House shot. The difference is very subtle, with just a slight boost to the shadows.
|Far Field DRO Levels|
|Level 1||Level 2||Level 3|
|Level 4||Level 5||Auto|
Above, you can see the effects of the five manual levels of DRO, plus Auto, on our Far-field House shot. Auto DRO produced results similar to the manual Level 1 setting, though not identical.
|Outdoor Portrait HDR Examples|
|HDR Off||HDR Auto||HDR 1 EV||HDR 6 EV|
(Levels adjusted equally in Photoshop on the right-hand side to show noise)
High Dynamic Range. The Sony A33's HDR mode takes three images in rapid succession, one at the nominal exposure, one underexposed, and one overexposed, then combines them into one high dynamic range JPEG automatically. Highlight areas from the underexposed image, shadow areas of the overexposed image, and properly exposed areas from the nominal image are combined in-camera to produce an image with increased dynamic range. The camera saves the composite image, as well as the one taken at nominal exposure. 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. The user manual warns that 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. As you can see, the Auto setting produced an image that looks quite flat and unnatural, roughly matching the 3 EV setting. The lowest manual setting of 1 EV did a great job however, taming highlights and boosting shadows without additional noise. In fact, shadow noise is lower since the overexposed image would have less noise in the shadows than the nominally exposed image. There may also be some blending going on, which would also average out random noise.
|Far Field HDR Example|
|HDR Off, 0 EV||HDR Auto, 0 EV|
Above is another example of the Sony A33's HDR mode at work. As you can see, both highlights and shadows are well preserved, with no noise penalty. The image does look a bit flat, though. If you look carefully at the full resolution HDR image, you will see some ghosting in the leaves, caused by movement from wind during the exposures.
|Far Field HDR Levels|
|1 EV||2 EV||3 EV|
|4 EV||5 EV||6 EV|
Above, you can see the effects of the six manual levels of HDR on our Far-field House shot, plus Auto. Auto HDR produced results similar to the manual 2 EV setting, though not identical.
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.)
Low light. The Sony A33 performed well in our low light test, producing bright images down to the lowest light level we test at (1/16 fc) at all ISO settings. The metering system struggled a bit at very low light levels though, so we used manual exposure for these shots (except for the Multi-frame NR examples in right-most column, which used Aperture-priority). Noise is very well controlled up to ISO 800, though as expected, at higher ISOs there are moderate to high amounts of fine luminance noise and some blotchy chroma noise. Auto white balance did a very good job here, producing a neutral color balance at all ISOs and light levels. There is just a hint of some horizontal banding at very high ISOs, but that's not uncommon. Hot pixels can be seen with long exposure noise reduction turned off (the second column from he right), even at ISO 100, but they are few and far between. The right-most column shows the results with Multi-frame Noise Reduction active. It really does a good job at reducing noise compared to a single frame at the same ISO and light level, though that's a little hard to tell from these shots, because the Sony A33's metering system underexposed them.
The camera's autofocus system was able to focus on the subject down to below the 1/16 foot-candle light level unassisted with the 18-55mm kit lens. That's excellent performance even for an SLR. The SLT-A33 was 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 like the Sony A33 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 Hand-Held Twilight|
|Manual, 1/30s, ISO 6400||Hand-Held Twilight, 1/60s, ISO 6400|
Hand-Held Twilight. A feature inherited from Sony's Cyber-shot point-and-shoot cameras, Hand-held Twilight mode shoots a burst of six images with a single press of the shutter button, using high enough sensitivity to hand-hold the camera in fairly low light. The A33 then combines all six source images into one image with reduced noise in static areas, as compared to a single shot taken with the equivalent exposure settings. In the example above, Hand-Held Twilight mode chose ISO 6,400 at a shutter speed of 1/60s. As you can see, the camera managed to get an image almost as sharp with similar noise while being hand-held (on right) as with the same ISO on a sturdy tripod, though the resulting image in this case is a bit dim. (We found this feature works better on real-world subjects such as poorly lit nightscapes.)
|Low Light Multi-frame NR|
|Manual, 1/4s, ISO 12800||Multi-frame NR, 1/10s, ISO 12800|
Multi-frame Noise Reduction. This new feature is similar to Hand-held Twilight mode, but gives you control over the ISO used, so you may still need to use a tripod depending on the ISO 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 clean 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, though the underexposure isn't really showing what the technique is capable of. An added bonus is that ISO 25,600 equivalent is available with MF NR.
Here's a better example of Multi-frame Noise Reduction at work using our Still Life target in good light at ISO 6,400:
|Normal mode, 1/1250s, ISO 6400||Multi-frame NR, 1/1250s, ISO 6400|
Print quality is very impressive, producing usable prints from every ISO setting.
ISO 200 shots also show excellent detail at 20x30 inches.
ISO 400 shots are slightly soft, but still show good detail at 20x30 inches.
ISO 800 images look great at 13x19, but were a little soft at 20x30 inches.
ISO 1,600 images print well at 13x19, with a little noise appearing in the shadows, but it's not as bad as on the A55.
ISO 3,200 files are a little too soft printed at 13x19 inches, but they look better at 11x14. There is some color fading, but it's not too bad.
ISO 6,400 shots are usable at 8x10, but really look better at 5x7.
ISO 12,800 images are a little grainy at 5x7, but shape right up when printed at 4x6 inches.
Overall, very impressive results from the Sony A33, producing a usable print from every ISO setting.
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.)
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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.