I assume that you know what digital slr cameras are, cameras that takes video or still photographs, or both, by recording images on a light-sensitive sensor.
Go here for Canon Digital SLR:s
Depending on if the mirror is up or down, the light can only reach either the viewfinder or the sensor. On most digital SLR cameras you can therefore not view the scene you are about to record on the LCD display.
The advantage of an optical viewfinder is that it shows the exact image that you are getting, you see the image throw the lens. There is no time lag as it is on compact cameras LCD:s or in electronic viewfinders.
A disadvantage of the optical viewfinder system is that you can't view the scene on the LCD monitor before you take the photo. Electronic viewfinders may be better in dim light because the display can be brightened up.
Some of the resent DSLR:s have something called live preview or "Live
View" which makes it possible to use the LCD monitor when you compose
When I write this in September 2008 many digital SLR cameras from the big manufacturers have the option for live preview.
As of 2008 both Nikon and Canon announced digital SLRs that records full motion video. The Nikon D90 is capable of 720p high-definition video while the Canon EOS 5D Mark II 21.1MP can record 1080p video.
If you follow the links above you can review the specifications and also order the cameras from Adorama. I bought my Canon 5D Mark II from Adorama.
Most cameras use either a CCD or complementary metal oxide semiconductor, or CMOS chip, as an image sensor. It seems that the best DSLRs are using a CMOS sensor.
The largest Digital SLR sensors are referred to as "full-frame", and are the same size as 35 mm film.
These sensors are used in professional DSLRs such as the Canon EOS-1Ds Mark III, Canon EOS 5D, Canon 5D Mark II, Nikon D700, Nikon D3, Nikon D3x and the Sony Alpha 900.
The more common DSLR:s uses a smaller sensor usually called APS-C sized, which is, approximately 23 mm x 15 mm or about 40% the area of a full-frame sensor.
The Four Thirds System sensor is 26% of full frame, APS-H sensors (used, for example, in the Canon EOS-1D series cameras) are approximately 61% of full frame, and the Foveon X3 sensor at 33% of full frame sensor.
The sensors used in DSLR:s are much larger than the sensors found in compact cameras, most use sensors known as 1/2.5", whose area is only 3% of a full frame sensor.
Even high-end compact cameras such as the Canon PowerShot G9 or the Nikon CoolPix P5000 use sensors that are approximately 5% and 4% of the area of a full frame sensor.
In general, a larger sensor have less noise, higher sensitivity, and increased dynamic range. There is also a relation between the digital camera sensor size and depth of field, with the larger sensor giving a shallower depth of field then a smaller size sensor.
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