SPEED/TIMING
Start-up to First Shot (Advantage: Nikon D80)
We test how long it takes for cameras to take a shot after they're turned on. For compact cameras, the delay can be a few seconds, long enough to miss a shot, but with DSLRs, it's usually pretty short. The Nikon D80 turned in the quickest time, at 0.45 seconds. The Canon Rebel XTi was next, at 0.54 seconds. The Sony Alpha A100 took noticeably longer – 1.05 seconds in our trials.
Though we set up our tests to control for the differences in ergonomics, the power switches of the cameras may have an effect on how quickly users get them going. The D80's switch is a ring around the shutter release, and is very quick to use. The Rebel XTi's switch juts out from the mode dial, and we found it natural to switch the camera on with the right thumb, while the index finder stayed on the shutter release. The Sony Alpha A100 has its power switch on the far left of the back. We didn't find that an easy spot to get used to, because we usually cradle a DSLR's lens with the left hand, so turning on the camera required changing our grip.
Shot to Shot (Advantage: Nikon D80)
The three cameras offer very similar burst modes, ranging from the Nikon D80's 2.8 frames per second, to the Rebel XTi's 2.7 fps, to the Sony Alpha A100's 2.5 rate. We used a 2GB SanDisk Ultra II compact flash card to evaluate the speed of the Canon and the Sony, and a Kingston 2GB SD card in the ND80. The neighborhood of 3 frames per second is useful for candids and action. Sports and news photographers will likely require more speed – the 5 fps offered by more expensive cameras such as the Nikon D200 or the Canon EOS 30D, or the 8 or 8.5 fps offered by the same companies' pro-level cameras for photojournalists.
The Alpha, D80 and XTi outdo their predecessors when it comes to the number of shots they can take in single bursts. The D80 managed an even 100 of its best JPEGs before pausing. The XTi rattled off a remarkable 69 of its best JPEGs before pausing. The Alpha just didn't stop – it kept shooting at 2.5 fps until it filled the memory card with JPEGs. In their RAW modes, the cameras shot shorter bursts. The Nikon D80 managed 15, and then paused 5 seconds before shooting again. The Rebel XTi shot 10, and needed a 6.5-second rest. The Alpha shot 13 RAW frames at 2.5 fps, and then slowed to 1.3 fps, but, once again, didn't stop until the card was full.
It's unlikely that many users will tax these cameras' burst capacities in JPEG mode, but for RAW shooters, 5 seconds could be a very long time to wait for the buffer to clear while shooting action. The D80's faster speed, combined with a respectable 15-frame burst in RAW mode, adds up to a better burst mode.
Shutter to Shot (Advantage: Canon XTi)
We test the time lag from the depression of the shutter to the actual shot, shooting a subject a few feet from the camera, with the lens set to autofocus, at wide-angle. If they were pre-focused, all of these cameras would perform much faster. The Sony Alpha A100 had a typical lag of 0.27 seconds in our test, while both the Nikon D80 and the Canon Rebel XTi lagged 0.18 seconds. The difference is noticeable in shooting sports or other action.
IMAGE QUALITY
Resolution (Advantage: Canon XTi)
Resolution measures the level of detail a camera can record in an image. We test resolution by photographing a standard ISO chart, and analyzing the images with Imatest software, an industry-standard software package for photographic testing. Imatest reports resolution results in line-widths per picture height (LW/PH), a measure that's appropriate to digital camera testing, because it is independent of the physical size of the sensor, and because it reflects the useful results that a camera can deliver in a print. Imatest also analyzes in-camera sharpening. All cameras process image data as they create either JPEG or RAW files, and DSLRs such as these three allow the user to adjust the amount of sharpening done in-camera. The more sharpening done by the camera, there will be less to do in post-processing on a computer.
We evaluated the resolution of these three DSLRs in two tests.The first looked at the maximum performance of each lens, at its optimal settings, while the other test was administered at the maximum aperture setting of f/3.5. For the first test, we determined the “sweet spot” of each particular kit lens by shooting the three cameras at a range of apertures and focal lengths, reporting the best results we got from each.
The Sony Alpha A100 delivered the best resolution scores of the bunch, with 1967 LW/PH horizontal and 1796 vertical in a shot taken at f/9 and 60mm. However, the image was slightly oversharpened: 2.27 percent horizontally and 1.37 percent vertically. The Canon Rebel XTi, shot in its Neutral Picture Style setting, came in at 1531 LW/PH horizontally and 1662 vertically, but was heavily undersharpened by 18.6 percent horizontally and 17 percent vertically. The Nikon D80 in its default parameters, resolved 1660 LW/PH horizontally and 1301 vertically, with undersharpening of 12.1 and 24.7, respectively. The differences in sharpening will likely cancel out the differences in LW/PH, and careful users will tailor any of these cameras to their needs – snapshooters who don't plan to tweak their images individually would probably do well to bump up the sharpening on the Canon or Nikon, but a photographer who plans to retouch images will have to decrease sharpening on the Sony Alpha A100. The Canon can be easily adjusted to perform more like the Sony, though with slightly less sharpening imposed, by selecting its Standard Picture Style. Users can increase the Nikon’s sharpening with a slider in the camera’s menu.
Nikon D80
Nikon D80 - Vertical Resolution
The story is similar with the apertures wide open. The Sony Alpha A100 delivered LW/PH scores of 2167 and 1940 horizontally and vertically, but had to work harder to maintain the same visible sharpness with more significant oversharpening of 9.73 and 7.31 percent. The Canon Rebel XTi delivered 1615 and 1507 LW/PH, undersharpening at 8.65 and 16.1 percent. The Nikon D80 scored 1423 and 840.8, undersharpening a whopping 24.1 and 32.3 percent. With apertures wide open on cheap kit lenses, these tests may say more about lens quality than the sensor, though it's clear that the Sony Alpha A100 is programmed more like a point-and-shoot camera and attempts to keep the images as snappy as possible. This forces users to dial down the sharpening levels to make them more adjustable in post-processing. The XTi and D80, by contrast, function more like typical DSLRs and leave room for users to sharpen files post-capture or adjust the levels in-camera to realize all the detail in the file. The Nikon and Camera design will be much more favorable to users familiar with SLRs, while the Sony design will be produce more visible detail out of the camera.
Nikon D80 - f/3.5
Canon XTi - f/3.5
Sony A100 - f/3.5
Moiré (Advantage: Nikon D80)
Moiré is the common term used for digital artifacts caused by incompatibilities between the pattern of photosites on an image sensor, and a pattern in the subject. It can show up as incorrect colors, odd curving patterns, or both. Each of the cameras were tested using its kit lens. In the samples from the Nikon D80, Sony Alpha A100, and Canon Rebel XTi, we see both effects, slightly. The three images are 100 percent crops 180 pixels square – they are very small sections of the images. In both the D80 and the XTi images, there is a color shift toward the center of the pattern. The XTi image shows a bit of pink above, below and to either side of the center. The D80 image simply looks a bit yellower in the middle. The effect is most visible in the Alpha image, which shows both warm and cool colors, and curving lines. Sharpening increases the moiré effect, and, as our resolution testing showed, the Alpha performs much more sharpening than the D80 or the XTi.
Sony A100
Nikon D80
Canon XTi
Noise (Advantage: Canon XTi)
Image noise in digital photos looks a bit like film grain or bad television reception. Its speckling appears random and sometimes with a pattern. It limits image quality by disrupting the rendering of texture, and if it's bad enough, by reducing resolution. We use Imatest software to measure noise in images with shots of a GretagMacbeth color chart. We test noise at each ISO setting.
Digital processing to remove noise is a balance, because it's hard to mathematically discern between image noise and fine detail. If the reduction is too aggressive, it reduces resolution and leaves surfaces looking unnaturally smooth. All commercial cameras perform some noise reduction. The Sony Alpha A100, Nikon D80, and Canon Rebel XTi all have user settings for noise reduction, so we tested the various settings.
The Canon XTi did best with noise reduction turned off, while the Alpha was far behind both the XTi and D80. Both the D80 and the XTi did much better with their reduction on, and both performed much better than the Alpha. The D80 has three noise reduction settings: “Off,” “Norm” and “High.” Over ISO 1000, there is a significant difference between Norm and High. The XTi's reduction setting performs somewhere between the D80's two settings.
Low Light – Night Scene (Advantage: Nikon D80)
We shoot a night scene with cameras to test their performance in low light, both at high ISOs and when using long exposures. The night scene shots were taken using a semi-automatic shooting mode and the camera’s automatic white balance setting. The D80 images looked more blue than the Alpha or the XTi images. The XTi images looked pink. The Alpha images seemed more neutral, but they were less saturated.
Click on any of the images below to view the full resolution file.
ISO 100
Canon XTi - ISO 100
Sony A100 - ISO 100
Nikon D80 - ISO 100
ISO 200
Canon XTI - ISO 200
Sony A100 - ISO 200
Nikon D80 - ISO 200
ISO 400
ISO 800
Canon XTi - ISO 800
Sony A100 - ISO 800
Nikon D80 - ISO 800
ISO 1600
Canon XTi - ISO 1600
Sony A100 - ISO 1600
Nikon D80 - ISO 1600
At 1600, the Alpha images had less contrast and were much noisier than the D80 or XTi images. At 1600, the D80 and the XTi maintained saturation better than the Alpha as well. The D80 looksed best to us because it maintained saturation of both blues and oranges. Though all the images shot at 1600 awere noisy, we noticed particular problems with the Alpha and XTi images – the Alpha's noise gets blotchy at 1600, looked less film-like, and therefore, it will look more distracting to many viewers. In the XTi image, the noise gets brighter – some of the pixels that are off-color are way off, rather than just slightly askew.
Long Exposures (Advantage: Sony Alpha A100)
At 30 seconds and ISO 400, the Sony Alpha A100 produced a neutral, but still saturated image, picking up the weird greens of the mercury vapor light and the nicotine orange of sodium lights, while managing a natural rendering of the facade of the facing building. On the other hand, the Nikon D80's 30-second, ISO 400 looks very green and too dark. The XTi managed a fuller exposure, but doesn't deliver the color contrast that the Alpha does. Noise is less of a problem at the long exposure than it was at the highest ISO.
Canon XTi - 30sec exposure, ISO400
Sony A100 - 30sec exposure, ISO400
Nikon D80 - 30sec exposure, ISO400
Dynamic Range (Advantage: Canon XTi)
The dynamic range of a printed photo runs from the pure white of the paper to the darkest black of ink or pigment. The dynamic range of a scene is usually much wider than that – it might run from the brightness of the sun to the darkness of a deep shadow. The challenge for camera designers is to develop cameras that can translate the very wide range of light and dark in the world into the more limited range of a print or computer monitor. We use Imatest software to measure how wide a range of brightness a camera can capture, and still show detail throughout the range. Imatest reports both high and low quality ranges. The high quality range shows the kind of smoothness that users expect in the most important parts of their subjects, while low quality has much more noise. Low quality range is important, though, because it adds texture to shadows and highlights.
The Sony Alpha A100 high quality range is about 8 EV all the way up to ISO 200, which is an excellent score among cameras we've tested. This result reflects the use of the Alpha's ISO 80 and 200 settings that are designed specifically to preserve highlight and shadow detail. (The Alpha's other dynamic range improvement system functions only in auto modes, which are not compatible with our dynamic range test.) The Alpha drops precipitously at 400, 800 and 1600, however. The Canon Rebel XTi and the Nikon D80 are closely-matched at ISO 100 and 200, though the XTi shows an advantage at 400 to 1600. So, though the Sony Alpha has an advantage at 200, the Canon Rebel XTi is the best performer overall, with superior high-ISO performance.
Color (Advantage: Canon XTi)
We test cameras' color performance by photographing an industry standard color chart manufactured by GretagMacbeth. We analyze the images with Imatest software, the leading package for this kind of measurement. Imatest measures saturation – whether the colors are too bright or too dull – as well as color error – whether the blues are greenish, or the yellow is too orange.
The Canon Rebel XTi is the standout in this test – its color error was significantly lower than either the Sony Alpha A100 or the Nikon D80, which scored very similarly, though the Alpha is slightly better at ISO 100 and 1600, and slightly worse in the middle of the ISO range.
Click on the images below to view the full resolution files.
Sony A100 - Standard
Nikon D80 - Normal
Canon XTi - Standard
Color Information - by channel
Blue Channel
Sony A100 - Blue Channel
Nikon D80 - Blue Channel
Canon XTi -
Blue Channel
Green Channel
Sony A100 - Green Channel
Nikon D80 - Green Channel
Canon XTi - Green Channel
Red Channel
Sony A100 - Red Channel
Nikon D80 - Red Channel
Canon XTi - Red Channel
White Balance (Advantage: Canon XTi)
White balance allows cameras to accommodate various types of lighting, each of which imparts a characteristic color on subjects. We test white balance by photographing a GretagMacbeth color chart in various lighting conditions, and analyzing the images with Imatest software. Imatest exaggerates color error to make it easier to see. We test the accuracy of each cameras' automatic white balance setting as well as their presets for various types of light.
Auto White Balance
Daylight
Nikon D80
Sony A100
Canon XTi
Tungsten
Nikon D80
Sony A100
Canon XTi
Fluorescent
Nikon D80
Sony A100
Canon XTi
Flash
Nikon D80
Sony A100
Canon XTi
All three cameras undercorrected tungsten light in their auto settings. That's probably strategic, because the warm tint they give is flattering for portraits. The Canon Rebel XTi also undercorrects tungsten light in its preset mode, leaving subjects a bit orange. The Nikon D80's tungsten preset corrects well, giving a neutral tone. Oddly, the Sony Alpha A100 overcorrects tungsten with its preset, giving a blue tint, which wouldn't be appealing in any situation we can think of, since it is neither accurate nor flattering.
The Sony Alpha A100 did a better job autocorrecting our fluorescent lights, while the Canon Rebel XTi and the Nikon D80 left a much more sickly green tint in their shots. All three cameras' presets rendered the light too blue.
Flash light looks purple under the Sony Alpha A100's auto white balance, and blue on the preset. The Nikon D80 gave a slightly green tint in auto mode, with a very neutral preset. The Canon Rebel XTi's auto mode and flash preset gave more or less identical results – they're a little pink, subtly flattering for human subjects.
White Balance Presets
Daylight
Nikon D80
Sony A100
Canon XTi
Tungsten
Nikon D80
Sony A100
Canon XTi
Fluorescent
Nikon D80
Sony A100
Canon XTi
Flash
Nikon D80
Sony A100
Canon XTi
All told, the Auto settings were problematic – the Sony Alpha A100 auto mode missed on flash and tungsten, with better performance on fluorescent. The D80's auto was off on flash, tungsten and fluorescent. The XTi's auto performance was off on the same three, though it erred in a better direction with flash.
Portrait (Advantage: Canon XTi)
Our portrait samples prompted thoughts of exfoliants and an eyebrow trim, but beyond mere vanity, they reinforce some of what we've noted in other testing. The Sony Alpha A100 image is oversharpened -- though not sharper than the Nikon D80 or the Canon Rebel XTi images. Resolution isn't a bad thing in portraits, but the detail in the Alpha image looks harsh. Shot under tungsten light, they show the Canon bias to keep tungsten images warm, and Nikon's neutral tone. The highlights in the Nikon image aren't as smooth as the Alpha or the XTi RAW Files. All in all, the Canon Rebel XTi produced the better portrait.
Sony A100
Nikon D80
Canon XTi
RAW Files – Underexposure (Advantage: Draw)
We shot RAW files of a still life with the three cameras set to various levels of underexposure, to see how well RAW files respond to adjustment. We used Adobe RAW converter to open the files, rather than the manufacturers' software. We don't claim this is an exhaustive test of the potential for RAW files, but we hope it's helpful to consumers who are considering shooting RAW with these cameras.
Simply put, RAW files are not a substitute for getting the exposure right, or for bracketing. The software impressively converted shots up to 3 EV underexposed, and recovered the acid colors of our convenience-store bouquet. There are drawbacks to the gambit, however: The underexposed shots are very noisy, and the noise increases significantly with 1 EV of underexposure. An underexposed image squeezes all the image data into the left side of the histogram, and data expansion appears to happen evenly across the range of tones available. In a well-exposed shot of our flowers, the background is just about dead black – it prints that way, at least. As the underexposed images were expanded, however, the converter found detail in the blackout cloth background as well as the flowers. It's impressive, but not helpful. We used the automatic settings on the converter, rather than tweaking manually, which could clearly have given us a black background.
Straight Conversion (no adjustment)
Sony A100
Canon XTi
Nikon D80
Auto Conversion (Adobe Camera RAW)
Sony A100 - automatic conversion
Canon XTi - automatic conversion
Nikon D80 - automatic conversion
It's not clear from these data whether one camera has a better RAW file that the others. To say that, we would have to do much more testing, beyond the scope of this review.
Parameters (Advantage: Canon Rebel XTi)
The Sony Alpha A100, the Canon Rebel XTi, and the Nikon D80 all bundle a range of image parameters including saturation, contrast and sharpening into sets. Canon calls them Picture Styles, Nikon calls them Image optimization and Sony calls them Color/DEC mode. With each camera, the sets can be fine tuned for saturation, contrast and sharpness, but the text descriptions suggest that some of the built-in options go beyond those three parameters.
All three cameras offer a black and white setting for shooting monochromatic images. All three also include dedicated Portrait settings, which and they generally do the same things – they make pinks more pure, to tone down blemishes, they cut sharpening, and they decrease contrast. The D80's Normal setting, and the XTi's and Alpha's Standard settings all boost saturation, contrast and sharpness. The XTi and the Alpha have Landscape settings, which boost saturation and sharpening. The D80 has a Vivid and a Vivid plus setting, which do the same things. The Alpha's Sunset setting is supposed to accentuate warm tones more than cool ones, and our trial images suggest that it does. The Alpha's Night mode adds tone to highlights without changing shadow values.
Click on the thumbnails below to view the full resolution files.
Black and White Mode
Nikon D80
Canon XTi
Sony A100
The Landscape, Vivid, Vivid plus, and Sunset settings all tend to block up the reds in the rose in our sample shot. When one looks at the separate color channels of the image, large patches of the shots taken in those modes have only red – no trace at all of blue or green. On the other hand, Canon's Neutral and Faithful modes tend to maintain at least a very low level in each channel. That's a big advantage for editing and printing the image – without those small variations, the red will posterize – turn into flat patches of color -- in printing.
Canon recommends shooting in Neutral or Faithful settings to preserve detail for post-processing, and Nikon says the same about its Softer setting. The other settings generally make it more difficult to post process images, by pushing colors to extremes, over-sharpening and losing detail.
Image stabilization (Advantage: Sony Alpha A100)
We use the term image stabilization to indicate any camera mechanism that prevents motion blur by physically moving something in the optical system, either an element of the lens, or the sensor. The Sony Alpha A100 has Super Steady Shot, which moves the sensor. The great advantage of this system is that the stabilization system works with every lens that fits the Alpha. Canon and 
Nikon have opted instead to make individual lenses with stabilization, but the kit lenses offered with the D80 and XTi are not stabilized. Both Canon and Nikon charge significantly more for stabilized lenses than regular ones, and they don't offer every focal length or aperture range with stabilization.
One argument against moving the sensor to manage vibration is that a moving system may let the sensor get out of alignment with the lens mount. Most compact cameras with fixed lenses and stabilization move a lens element, because the lenses are smaller, lighter and therefore easier to move.
We compared the Sony Alpha A100 stabilization system with a Nikon 24-120mm VR lens mounted on the D80 (VR is Nikon's trade name for optical stabilization) and the Canon Rebel XTi, with its unstabilized kit lens. The idea of this test is to illustrate the effectiveness of the Alpha’s in-camera stabilization system compared to a moving lens system.
We shot part of our ISO target hand-held with each camera at 1/15 of a second, with stabilization on and with it off. Both the Sony and Nikon stabilization systems were effective in our test, but given the variables in our test, our results shouldn't be used to try to identify a superior system. The point is more to indicate whether the Sony system is effective and what advantage is offered by a camera that comes with a system built into the camera design.
Sony A100 - Super SteadyShot ON
Nikon D80 - VR ON
Canon XTi - No image stabilization
