The basic operation of a DSLR is as follows: for viewing purposes, the mirror reflects the light coming through the attached lens upwards at a 90 degree angle. It is then reflected three times by the roof pentaprism, rectifying it for the photographer's eye. (Note that the diagram below incorrectly shows a non-roof pentaprism.) During exposure, the mirror assembly swings upward, the aperture narrows (if stopped down, or set smaller than wide open), and a shutter opens, allowing the lens to project light onto the image sensor. A second shutter then covers the sensor, ending the exposure, and the mirror lowers while the shutter resets. The period that the mirror is flipped up is referred to as "viewfinder blackout". A fast-acting mirror and shutter is preferred so as not to delay an action photo.Nikon D7000
Just a few weeks after Canon dropped their EOS 60D on us, Nikon fires back with their new 16.2 megapixel DX-format DSLR.
The D7000 — not to be confused with their recently-announced compact, the P7000 — uses a CMOS sensor and the EXPEED 2 image processing engine, which Nikon claim combine to provide low-light performance that's unmatched with an APS-C sensor. It has a native ISO range of 100-6400, but can be expanded all the way up to 25,600.
Its accompanied by a revamped 39-point AF system with a new 2,016 pixel RGB 3D Matrix Metering system to better handle a wider variety of challenging shooting situations. It uses nine center cross-type sensors and allows shooters to switch between dynamic or single point AF. The Scene Recognition System also dips into a database of more than 30,000 images to optimize focus, exposure and white balance. Nikon D7000 Shoots 1080p Video With Full-Time Autofocus
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