佳能重磅DSLR透视
by Stephen Shankland
Cameras have always been marvels of miniaturization, but with the switch to digital technology, engineers have had to squeeze electronics and computers into camera bodies already filled with mechanical and optical components.
Most folks only see the outsides of cameras, but the insides can be works of engineering art, too. Canon\'s latest SLRs, the $8,000 EOS-1Ds Mark III and $1,300 EOS 40D, are a good case in point.
Here are some of the views I found most interesting.
Inside-out 40D
(Credit: Canon)
I like this shot as much for the drafting prowess as the assembly of innards it shows. It gives a more direct appreciation of just how little empty space there is inside a 40D. Clearly subsystems such as autofocus, image processor, display and sensor must be designed not to elbow in on other components\' turf. It must be a terribly complicated exercise in three-dimensional visualization.
1Ds Mark III\'s chassis
(Credit: Canon)
If you dropped this camera on your foot, the camera would probably come out ahead. Its internal chassis and mirror box are made of magnesium alloy. The camera is 6 oz. lighter than its predecessor, though, the 1Ds Mark II.</ br>
Weather sealing
(Credit: Canon)
To keep out water and dust, the 1Ds Mark III has weather seals at 76 locations such as around buttons, dials and switches.
Humongous sensor
(Credit: Canon)
Canon can only get 20 full-frame sensors from each wafer, apparently a standard 200mm-diameter slice of silicon crystal--assuming that there are no duds. That manufacturing and research expense contributes to the camera\'s $8,000 price tag. Full-frame sensors measure 36x24mm, the size of a frame of 35mm film. Most digital SLRs, including Canon\'s 40D, use smaller sensors that are considerably cheaper to make.
The 40D\'s double motors
(Credit: Canon)
The 40D has two motors, one to operate the shutter and another to flip the reflex mirror up (which means light coming through the lens heads for the sensor instead of the viewfinder).
Computing horsepower
(Credit: Canon)
It takes a lot of computing power for the 40D to process its images--it can shoot as many as 6.5 frames per second, pulling each 10.1-megapixel image of the sensor, processing it, then sending it to a DDR memory buffer before it\'s written to a flash card. The 40D uses a single Digic III image-processing chip, but the 21.1-megapixel 1Ds Mark III uses two in parallel.
1Ds Mark III prism
(Credit: Canon)
In most SLRs, a prism sits atop the lens, redirecting light from the reflex mirror to the viewfinder. Larger prisms typically mean better magnification and a more complete view of what actually will be photographed, but also mean a heavier, more hulking camera.
