Live preview, or the ability to see the changing scene through the lens on a
digital camera’s LCD, is something we now take for granted on compact digital
cameras. When in capture mode, even the most inexpensive point-and-shoot will
display the changing scene in front of the lens on the LCD, which is itself a
species of live preview.
Live preview allows a
digital camera's electronic display to be used as a
viewfinder, that is, as a means of framing and previewing before taking the
photograph. In most such cameras, the preview is generated by means of continuously and directly projecting the image formed by the objective lens onto the main image sensor, which in turn feeds the electronic screen with the live preview image. The electronic screen can be either a
liquid crystal display (LCD) or an
electronic viewfinder (EVF).
While some types of digital cameras trace back their origin to a corresponding type of film still cameras (for example digital single-lens reflex cameras "DSLRs" to
film single-lens reflex cameras "SLRs"; digital
rangefinders to film rangefinders, etc.), cameras with live preview also derive from electronic (video) TV cameras.
Most early digital cameras through 1995 did not have a live preview; most
digital single-lens reflex cameras still do not have this feature, as it is fundamentally incompatible with the single-lens reflex mechanism. The first digital still cameras with an
LCD display and live preview were the Casio QV-10 and Ricoh RDC-1 in 1995. The first DSLR to use live view was the fixed-lens Olympus E-10, from 2000; the first interchangeable-lens DSLR to use live view was the Olympus E-330 of 2006.
Compacts & bridges, the low- and high-end cameras with live preview
Live-preview cameras include two different but not so distinct categories:
Bridge digital cameras and Digital Camera Review by Gene Wrights.
Bridge cameras in general are higher-end and more advanced (feature-packed), expensive (higher build quality) and sizable than the
DSLRs, cameras usually without live preview
When considering the advantages and disadvantages of DSLRs, the comparison is usually made between the best bridge cameras, and the smallest and cheapest DSLRs, so most of what can be said in this respect is treated in the
bridge camera article. Check in particular the following sections in that article:
One single fixed but versatile lens
LCDs and EVFs as principal viewfinders
A comparison between compacts and DSLRs would be really a very contrasted one in terms of size, weight, price, capabilities and image quality.
Almost all modern bridges and
compact cameras have a movie mode, while no DSLR offered this option until the
Nikon D90 released in August 2008. DSLRs have faster performance than other cameras in many areas (for example, start-up time, shutter lag, continuous mode, autofocus). This means that DSLRs are more reliable in certain situations, such as sport or action photography, where being late for a fraction of a second may result in missing the right moment of taking the picture. The idea that DSLRs perform better than other cameras in high ISO settings has to do primarily with the sensor size of the camera, not whether it has live preview. DSLRs always have large
sensors while a great majority of other cameras have a small sensor (notable exceptions being the Sony R1 and the Sigma DP1).
Live preview in some or all of these cameras is not conventionally generated (the image formed by the lens is either not directly or not continuously projected over the main sensor). Also the live preview in these DSLRs does not typically serve as their principal means of framing and previewing before taking a photograph. (As DSLRs, they have an optical view reflected in the OVF (Optical Viewfinder) for that purpose and the live preview is an additional feature).
While live-preview technology has been advancing, as for March 2008, there are no DSLRs which show a live preview as seamlessly as a fixed-lens camera. The main issues are with slow focus and lack of exposure-priority display. Among the DSLRs that do manage to focus using the standard phase-detection sensor used by DSLRs, none has managed to show 100% frame coverage like conventional digital cameras, thereby removing the key advantage of live preview over optical viewfinders. Additionally, 100% coverage optical viewfinders have recently become more common and affordable with the appearance of the
Nikon D300 and Olympus E-3.