One thing that people often find frustrating when upgrading from a compact camera to a DSLR is that they get used to composing their pictures on their compact camera by using the screen on the back of the camera. Moving up to a DSLR and having to hold it to your eye and look through the viewfinder may not come naturally, and many users prefer to have a bigger brighter view to show them what the camera is going to capture - that's where live view comes in.
Live view is the system that takes what the lens is seeing and, instead of directing it via the mirror to the viewfinder, projects it, electronically, onto the camera's rear screen. Using this can be very helpful for composing in tricky situations, such as when the camera is mounted on a tripod at an awkward height for trying to get your eye behind the viewfinder, or when shooting over people's heads, or when you want to shoot close-ups of flowers without getting your knees muddy!
Another great feature that can help when composing your picture is a 'flip-out' or articulated screen. Some models allow you simply to angle the screen to make it easier to see when you hold the camera up high or down low, while other models have screens that can twist and rotate to allow virtually any viewing angle. Sony pioneered the articulated screen, but more and more models are now using this idea, such as Nikon's D5100 and the latest Canon models the EOS 60D and 600D.
[Note - I have already given an explanation of difference between phase detect and contrast detect systems, but the following makes clearer how they relate to live view.]
Autofocus when using live view can be more of a challenge. The quickest focus mode, the phase detect method, relies on the mirror directing the image to the focus sensors, but using live view to project the image onto the rear screen requires the mirror to be moved out of the way. Some models can therefore only use the slower contrast detect method to focus in live view. More expensive models offer a choice, but when using phase detect the mirror has to be flipped back into position in order to focus, causing the screen to black out temporarily, which can be disconcerting. Contrast detect may be slower but the mirror is not needed and so there is no screen blackout.
Digital SLR Basics
Digital SLRs and Digital Cameras Key Differences
Digital SLR or Compact System Cameras
Digital SLR Handling
Help for Beginners
Lenses and Accessories
Buying a Camera Lens
Digital SLR Accessories
Learn More About Features
Resolution and Sensor Size
Manual Exposure Modes
Help With Tricky Lighting
Live View and Articulated Screens
Depth of Field Preview Button
Current and Recommended Models
Summary of Current Models
Recommended Digital SLRs
Digital SLR Guide Author
This guide was written by Ian Younger
Live view is not only a compositional aid, however. It can act as a 'live preview' of what your picture will look like, so, on some models, as you change your aperture and shutter speed you can see the view on the screen getting lighter or darker, and you can also see instantly the effect of changing the white balance setting or using one of the creative picture style effects. Again, users of compact cameras will be used to this, and, nowadays, most DSLRs have live view, but you may find it absent on some entry-level models, such as the Sony A290. Some higher-end models, such as the Nikon D300s, also lack live view, perhaps because it used to be seen as a little 'gimmicky' on a 'serious' camera.
Another benefit of using live view is that it can help with more accurate focusing. Most models allow you to zoom in or magnify the image on the screen, allowing you to check that specific elements in your picture are sharp, or take manual control over the focus to make sure it will be spot on.
An additional advantage of live view over simply relying on the viewfinder is that most viewfinders do not allow you to see quite to the edges of the image produced by the lens. Typically the viewfinder only shows about 95% of the picture area, which means when you take the picture it will show a little more around the edges than you were able to see in the viewfinder. More expensive models, however, such as the Pentax K-5 or Canon 7D, offer 100% viewfinder coverage, for a true 'wysiwyg' (what you see is what you get) view.