Canon EOS 350D Digital RebelCanon makes an impressive update to their wildly popular "Digital Rebel."!<<Viewfinder :(Previous) | (Next): Exposure and Flash>> Page 7:OpticsReview First Posted: 3/23/2003, updated: 6/4/2005 |
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Like most digital SLRs, the sensor in the EOS 350D is smaller than a 35mm film frame. This means that the "effective" focal length of standard EF lenses will be 1.6x their normal values on 35mm cameras. Just to be clear, nothing's changed about the lenses or their behavior, it's just that the CMOS sensor is effectively cropping a smaller area out of the lens' coverage circle. The net result is that shooting really wide angle photography is tough with digital SLRs, the 350D included. At the other end of the scale though, it's like having a 1.6x teleconverter on your lenses with no cost in light loss or sharpness. Thus, a 350mm telephoto has the same "reach" as a 480mm on your 35mm film camera. And of course, a f/2.8 350mm is a lot cheaper than a f/2.8 500mm! The net of it is that a 31mm focal length has the same angular coverage as a 50mm lens on a 35mm SLR, and the common 16-35mm zoom lenses have a range equivalent to 25.6-56mm on film cameras. Taking the 18-55mm EF-S lens as a case in point, its focal length translates into an equivalent of ~29-88 mm. (A slightly wider than average wide-angle to a modest telephoto.)
Autofocus System
Like the 300D, the 350D has an autofocus system with seven sensors, arrayed in a cross pattern in the center of the frame. You can manually select which of these you want the camera to pay attention to (handy for off-center subjects), or you can let the camera decide. When it's operating in automatic AF mode, it will use the sensor corresponding to the part of the subject closest to the camera. The EOS 350D's AF system operates in One Shot, AI Focus, or AI Servo AF modes, and in an excellent improvement over the previous Digital Rebel, the Rebel XT allows you to choose the focus mode in Program AE, Shutter Priority, Aperture Priority, or Manual modes. AI Focus AF mode automatically flips between One Shot and AI Servo AF modes, depending on the subject. If the subject remains stationary, the camera remains in One Shot AF mode. However, if the subject begins to move, the camera automatically switches over to AI Servo AF and begins tracking the subject as it moves. This is a handy feature, letting you automatically track moving subjects without having to manually adjust the focus mode. When shooting in any of the Basic Zone exposure modes (Automatic or the preset scene selections), the 350D locks the focus mode to One Shot or AI Servo and doesn't switch between the two modes. The AF system's low light limit is EV 0.5, which combined with the AF assist lamp, provides excellent focusing in dim lighting conditions. The Digital Rebel XT 350D also offers what Canon terms "Predictive AF," which basically calculates the rate at which a subject is approaching or receding from the camera, and then accurately focuses based on the subject's predicted position. (A feature that sports photographers will no doubt appreciate.)
Canon rates the performance of their AF systems by the point at which they cease to be able to track an object moving at a constant speed toward the camera, using a given lens. The closer an object gets, the more rapidly the lens mechanism must turn, so whether an AF system will keep up is largely dependent on the lens in use, it's focus speed, and the camera processor's ability to evaluate a changing scene. While I don't have explicit performance numbers for the Digital Rebel XT, Canon tells me that performance is similar--but not equal to--the EOS 20D. Using Canon's EF 350/3.8 IS USM lens as the basis of comparison, the EOS 20D can track an object moving at 30 mph (50 kph) down to a minimum distance of 26.4 feet (8 meters). A Canon white paper on the Digital Rebel XT reports a more impressive-sounding statistic: "With an EF 300mm f/2.8L IS USM lens, it can focus track a subject approaching at 186 mph up to about 66 feet away."
Manual focus is also available with any of the Canon EF and EF-S lenses, simply by sliding the AF/MF switch on the lens barrel.
AF-Assist Illuminator
Like the first Digital Rebel, the Digital Rebel XT uses the built-in flash head as its AF-assist illuminator, rather than a bright light built into the camera's body. This works well (as you'd expect, the flash is quite bright, and probably has a longer range than an on-body illuminator bulb), but the Rebel XT shares the limitation with the original Rebel that the AF-assist option is only available when a flash is in use (whether internal or external). That is, you can't use the AF-assist illuminator and also make an available-light exposure. If you attach a 550EX external flash unit to the 350D, its internal infrared AF-assist illuminator can be used instead of the flash head itself, providing a useful working range of about 50 feet with a less obtrusive light source. This AF-assist is still only available when the flash is enabled though. For non-flash photography, Canon's ST-E2 wireless sync transmitter can also be used for AF assist, a handy trick. The ST-E2's AF-assist light has a useful range of about 25 feet.
Sensor Cleaning!
Everyone understands that lenses sometimes get dust on them and need to be cleaned, and there are a lot of lens-cleaning cloths, solutions and other accessories on the market that work well. BUT, what do you do when your sensor gets dusty? Dust specks on the sensor tend to show up when shooting at very small apertures, appearing as dark blobs on your images. They're distracting at best, a terrible nuisance at worst, if you end up having to retouch every image to rid of them.
Most of us are naturally leery about the idea of poking around inside the delicate innards of our d-SLRs to wrestle with recalcitrant dust specks. Gently blowing the sensor surface (actually, the surface of the anti-aliasing filter) with compressed air gets rid of some dust, but there's invariably a lot that just stays stuck, no matter what. So what do you do?
If you've got dust specks on your sensor (and sooner or later you will), you're going to need to clean it. There are a lot of products out there intended to address this need, but a distressing number of them work poorly (if at all), and many are grossly overpriced. Advertising hype is rampant, with bogus pseudo-scientific jargon and absurd product claims run rampant. And prices - Did I mention prices? How about $100 for a simple synthetic-bristle brush?
So how do you know what product to use?
We don't pretend to have used everything currently on the market, but can tell you about one solution that worked very well for us. The "Copper Hill" cleaning method is straightforward and safe, and in our routine usage here at Imaging Resource, highly effective. Better yet, the products sold by Copper Hill Imaging are very reasonably priced. Best of all, Nicholas R (proprietor of Copper Hill) has put together an amazingly detailed tutorial on sensor cleaning, free for all.
Sensor cleaning is one of the last things people think about when buying a d-SLR, but it's vital to capturing the best possible images. Take our advice and order a cleaning kit from Copper Hill right along with your d-SLR, so you'll have it close at hand when you need it: You'll be glad you did!
(Other than a few backlinks on their site, we receive no promotional consideration from Copper Hill. We just think their sensor cleaning products are among the best on the market, and like their way of doing business. - We think you will too. Check them out.)
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