The Canon EOS 50D will work with pretty much any EF-mount lens ever made, as well as with the special EF-S lenses designed for cameras with APS-C size sensors.
The 50D hasn't changed its autofocus sensor layout or design from the previous model, the 40D. SLR autofocus accuracy is governed in part by how far apart you can space the sensor elements for a single AF point.
The AF points on the Canon 50D cover about 60% of the frame width, and about 50% of the frame height. The Canon 50D uses the built-in flash head as its AF-assist illuminator, rather than a bright light built into the camera's body. First introduced on the Canon Rebel XTi, Canon's system-wide approach to reducing the impact of dust on the image sensor is also included on the Canon 50D. The principal approach other manufacturers have used to deal with dust has been to make the system self-cleaning, by rapidly vibrating either the anti-aliasing filter itself or a protective cover glass lying above it, to shake loose adhering dust particles.
In typical fashion, Canon's camera engineers took a comprehensive look at the issue of sensor contamination, and came up with a multifaceted, system-wide approach to reducing the impact of dust on users' photographs. Canon's approach uses a vibratory cleaning method as a primary part of the overall strategy, but they've introduced several refinements as well. It's critical for a digital camera to power up and be able to capture the first shot quickly, to avoid missing the action when first starting up.
It turns out that only some of the dust that appears in DSLR images comes from outside the camera: As they age, normal wear and tear can make shutter curtains shed microscopic particles that eventually end up on the sensor. Along with the specially treated shutter, Canon has also begun using a different plastic in their DSLR body caps, one less prone to creating shavings that can drop into the mirror box. Rather than introducing a separate cover glass into the optical chain, Canon has split the Canon 50D'S anti-aliasing filter into two parts. In describing the technology, Canon notes that the outer anti-aliasing element is positioned further from the sensor surface (a millimeter or so) than is normally the case.
Previous models in this line of Canon cameras used an anti-static coating on the anti-alias filter to make it harder for dust to gain a foothold in the first place. No matter how good an automatic cleaning system, there are going to be some stubborn dust particles that it can't dislodge.
This sort of image processing to eliminate dust isn't an entirely new development, it's been a feature of Nikon's Capture software for some time. Canon's anti-dust approach is also different in that the dust map ("Dust Delete data") that the software uses to perform its magic is stored in the headers of the JPEG or RAW files created by the camera. We don't have any quantitative way of evaluating dust-removal systems, but based on Canon's description of it, their anti-dust technology does appear to go a step or two beyond anything else currently on the market, providing a more comprehensive solution to the problem of dust in DSLR images than we've seen to date. Despite the many advances in Canon's anti-dust technology, though, we feel compelled to point out that we've thus far seen no anti-dust system that completely eliminates the need for sensor cleaning. The Canon 50D is offered with an 28-135mm IS kit lens, with a fairly generous optical zoom range of ~4.8x, but an odd focal range for a sub-frame camera. As with zoom performance, the Canon 50D's macro performance will depend entirely on the lens in use.
The Canon 50D's 28-135mm IS kit lens produced about 0.6 percent barrel distortion at wide-angle, which is slightly below average among the cameras we've tested, but still noticeable in some of its images. Our take on this is that the very small pixels of the 50D are a challenge for this somewhat older lens design. These diagrams shows the basic sensor layout, first in the viewfinder, then on the AF sensor itself.
The diagram top right shows some odd arrangements that don't seem to agree with the diagram below, which has neat little plus symbols over each point.


The illustration above shows the relative spacing between the various AF points, with the distances between them marked in millimeters, at the focal plane. In practice, this works well: the flash is quite bright, and probably has a longer range than an on-body illuminator bulb. From the beginning, every DSLR has offered a sensor-cleaning mode, in which the mirror is locked up and the shutter opened to permit the sensor to be cleaned with compressed air, a solvent-carrying swab or other means.
This expands creative options enormously, but every time the lens is removed, dust from the environment is free to enter the camera body. Once dislodged, a strip of sticky material at the bottom of the sensor cavity or mirror box catches and holds them.
Some cameras with integrated cleaning systems can take a second or two for the cleaning cycle to complete before they're ready to capture an image.
In the Canon 50D, Canon has introduced a special shutter-curtain coating designed to greatly reduce the shedding of particles. This greater distance reduces the effect of any dust that does adhere, by making the shadow cast by each dust particle larger and softer-edged. Canon has developed a new fluorine-based coating for the 50D, which purportedly improves this dust resistance property. To deal with these, the Canon 50D has the ability to shoot a dust reference photo, and then transfer that information to Canon's Digital Photo Professional software, which can use it to eliminate the shadows cast by dust particles on the images. Canon's implementation has some additional wrinkles that make it somewhat more useful, though. There's thus no need to keep track of a separate dust image file, the information is always available in the file headers, assuming you've actually performed the dust-mapping process. Starting in the upper left from Shooting Menu Screen 2, selecting Dust Delete Data produces a screen that shows when the last Dust Delete reference image was captured.
Sooner or later, you're going to need to clean your sensor, so we strongly recommend purchasing a good-quality sensor cleaning kit right along with your DSLR. The 35mm equivalent range is about 45-216mm, which isn't wide at all at the wide-angle end. At the telephoto end, the 0.2 percent pincushion distortion is quite low and not as noticeable. Material on this site may not be reproduced, distributed, transmitted or otherwise used without the prior written consent of The Imaging Resource.
EF-S lenses can't be used on full-frame Canon cameras, nor on their models with 1.3x crop factors, like the current EOS-1D Mark III, but small-sensor cameras like the 50D can use any full-frame lenses in Canon's arsenal. For example, a 100mm lens on the Canon 50D will show the same field of view as a 160mm lens on a camera with a 35mm frame size.
It's priced at an average of $450 on its own, and reflects only about $200 difference between the kit and body-only suggested retail. You can disable the 50D's internal flash (or external Speedlite) by going into the Flash Control menu, which still lets the AF-assist pulses to fire; but then you lose your flash capability until you turn it back on. As the market has matured and more DSLRs have found their way into the hands of novice users, it has become clear that some automated way of dealing with sensor cleaning is needed. From there, it's only a matter of time before some of it makes its way to the surface of the sensor where it casts shadows that appear as dark blobs in your images. This approach was pioneered by Olympus, but has since been adopted by Canon, Nikon, Pentax, and Sony.
To avoid this problem, the Canon 50D aborts its normal power-on cleaning cycle as soon as the user touches the shutter button.
Dust particles frequently carry static charges, so the anti-static coating avoids one of the key mechanisms by which dust particles adhere.


You can update the Dust Delete data any time you think the camera might have been exposed to dust, or after you've manually cleaned the sensor.
Selecting OK on this screen initiates a cleaning cycle, after which the camera prompts you to take a picture of a blank white surface.
Automated anti-dust systems like Canon's will certainly help with some of the dust, typically the dust that the nylon brush-based cleaning systems can also handle. Resolution and detail were high, though with moderate softening in the corners from the lens. This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).
That double zig-zag center sensor array, the one that runs from top to bottom down the center (marked in yellow at right), serves the top, center, and bottom AF points.
You can build sensors with wider baselines, but that also restricts the range of lenses they can be used with. In truth, it's the anti-aliasing filter that collects dust, rather than the sensor itself, but common parlance refers to "sensor cleaning." For the sake of familiarity, we'll generally refer to sensor cleaning here, but will make mention of the anti-alias or low-pass filter as seems appropriate. The latest dust map is automatically incorporated into the EXIF headers of all JPEG images, or the headers of any RAW files.
An average performance here, especially considering this is a full-frame lens where much of the captured image should be in the sweet-spot of the image circle. Be sure to click on the Blur Index chart for an interactive look at how the lens performs across its range of apertures and zoom settings, as well as our reports on its chromatic aberration, vignetting, and distortion characteristics. The two yellow sensors in the middle are special, as they're essentially reprogrammable on the fly, able to be considered as part of each of the three center AF points, or taken together as one large sensor for extremely out-of-focus subjects. For non-flash photography, Canon's ST-E2 wireless sync transmitter can apparently also be used for AF assist. While we don't have any technical details on how the dust map is stored, Canon claims that the encoding scheme used for it is very efficient, so the dust map information adds very little to the file size.
If the surface you used to capture the image wasn't sufficiently uniform, you'll get an error message, but if the image was good, you'll see the confirmation screen as shown above in step 6. We ourselves use and recommend products from Copper Hill, which we've found to be both highly effective and among the most reasonably priced on the market.
If your budget will support it, the best package might be to get the 28-135mm kit lens and the EF-S 18-55mm IS model as well. As for their zig-zag arrangement, that just means that one sensor is slightly offset from the other, such that if you were to look at them magnified, one pixel would be slightly off from the other, zig-zagging back and forth like tires on an endurance course. The Dust Delete Data just generated will now be included in the headers of any JPEG or RAW images captured, until you decided to capture a new dust reference image. Results at full telephoto are similar with softness across the frame and again, moderate levels of chromatic aberration. That would give you good image quality in the 18-55mm range (the 18-55mm IS is a surprisingly good lens for the money), as well as the longer reach of the 28-135mm for more distant subjects, all with image stabilization. Thus, horizontal lines that would have been missed by one sensor can be picked up by the other.
We liked this lens when we tested it for SLRgear a while back (see our Canon 28-135mm IS review for those details), but it may be that it's just not up to the challenge of a 15MP sensor. All in all, the EF 28-135mm IS has about average performance for a kit lens, but we really think the average user will want something that starts a little wider.



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