Canon EOS 20DBy: Shawn Barnett and Dave EtchellsSlightly smaller and lighter upgrade brings greater speed and ease of use along with higher res and lower image noise. <<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 6:OpticsReview First Posted: 08/19/2004, Update: 11/19/2004 |
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Like most digital SLRs, the sensor in the EOS 20D is smaller than a 35mm film frame. This means that the "effective" focal length of your 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 using regular EF lenses. This has all changed, now that the new wide angle 10-22mm USM lens is available. 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 300mm telephoto has the same "reach" as a 480mm on your 35mm film camera. And of course, a f/2.8 300mm 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, the common 16-35mm zoom lenses have a range equivalent to 25.6-56mm on film cameras; and the new 10-22mm will be equivalent to a 16-35mm.
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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