Wednesday, January 24, 2007
Buyer's Guide 2006: Today's Digital SLRs
Features and resolution distinguish the latest cameras
APS And Full-Frame Sensors
Photographers who use 35mm lenses immediately notice the difference in magnification that occurs when those lenses are mounted on a D-SLR. This is because most D-SLR sensors are smaller than a standard 35mm frame. Named after a film format released in the '90s, an APS-size sensor measures approximately 15x23mm. Because the light from the rear of the lens is covering a smaller surface area, the lens delivers an image that looks as if it was taken with a longer focal length.
The lens magnification factor, which often ranges between 1.3x and 1.6x, increases the effective focal length of an attached lens. A 300mm lens, when mounted on a camera with a lens magnification factor of 1.5x, will perform as a 450mm. This occurs with no loss of light as would be experienced with the use of a teleconverter. For photographers who prefer to use their existing lenses at their "true" focal length, however, the Canon EOS-1Ds Mark II and EOS 5D are full-frame digital SLRs whose sensors have the same dimensions of a 35mm frame.
Nikon takes advantage of this lens magnification factor in the High Speed Crop (HSC) mode of its D2x camera. The 12.4-megapixel camera normally features a 1.5x magnification factor, but in HSC mode, the camera's resolution is reduced to 6.8 megapixels. By using a smaller area of the CMOS sensor, lens magnification increases by 2x, making a 300mm ƒ/2.8 lens into a 600mm.
Olympus has based its cameras on an entirely new system. Using a Four Thirds sensor, Olympus SLRs allow for the creation of optics that have been specifically designed for digital image capture. In addition to being lighter and more compact than comparable focal lengths, these lenses also promise improved color and tonal rendition while delivering excellent sharpness.
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