A Nikon D90 in "liveview" mode
In
digital photography,
live preview is the feature that 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).
Historical background
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.
Until 1995 most digital cameras 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 swinging-mirror
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
Canon EOS 20Da, a
special version of the
Canon EOS 20D
with modifications for
astrophotography. The first general-use
interchangeable-lens DSLR with 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
Compact digital
camera. Bridge cameras in general are higher-end and more
advanced (feature-packed), expensive (higher build quality) and
sizable than the compacts.
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:
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 is not a feature of the DSLR
type, but simply improved functionality of more expensive camera
models. Consequently DSLRs are more suitable for situations, such
as sport or action photography, where a fraction of a second more
delay between pressing the shutter release and exposing may result
in missing the right instant. Cameras with larger sensors perform
better than cameras with smaller sensors in
low-light
situations, with less
optical noise in
the image; DSLRs have larger sensors than most digital non-SLR
cameras, leading to better images. Non-DSLR digital cameras with
large sensors are available; for example the
Sony R1,
Sigma DP1, and
Panasonic Lumix
DMC-G1/GH1.
Digital SLRs with live preview
Live-preview functionality is becoming more and more common on
digital SLR cameras, and as of mid 2008 almost all new DSLRs have
the feature. The following is a partial list of DSLRs with live
preview:
- Canon 20Da,
40D, 50D,
450D, 500D, 1000D,
1D Mark III, 1Ds Mark III, 5D Mark II, 7D, 1D Mark
IV
- Olympus E-10, E-20,
E-330, E-410, E-420,
E-450, E-510, E-520,
E-620, E-30, E-3
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, Olympus E-3 and the Pentax
K-7.
Digital camera backs with live preview
Phase One
See also
References
External links
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