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The viewfinder is the "window" you look through to
compose the scene.
We will discuss the four types of viewfinder commonly found on
digital cameras.
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Optical
Viewfinder on a Digital Compact Camera
The
optical viewfinder on a digital compact camera consists of a
simple optical system that zooms at the same time as the main
lens and has an optical path that runs parallel to the camera's
main lens. These viewfinders are small and their biggest problem
is framing inaccuracy.
Since the viewfinder is positioned
above the actual lens (often there is also a horizontal offset),
what you see through the optical viewfinder is different from
what the lens projects onto the sensor.
This "parallax error" is most obvious at relatively
small subject
distances. In many instances the optical viewfinder
only allows you to see a percentage (80 to 90%) of what the
sensor will capture. For more accurate framing, it is
recommended to use the LCD instead. For
those who wear corrective glasses it's worth checking to see if
the viewfinder has any diopter adjustment.
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Because
the optical path of the viewfinder runs parallel to the
camera's main lens, what you see is different from what
the lens projects onto the sensor.
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Sometimes
optical viewfinders have parallax error lines on them to
indicate what the sensor will see at relatively small
subject distances (e.g. below 1.5 meter or 5 feet).
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LCD on a
Digital Compact Camera (TTL)
The
LCD on a
digital compact camera shows in real time what is projected onto
the sensor by the lens and therefore avoids the above parallax
errors. This is also called "TTL" or
"Through-The-Lens" viewing. Using the LCD for framing
will shorten battery life and it may be difficult to frame
accurately in very bright sunlight conditions, in which case you
will have to resort to the optical or electronic viewfinder (see
below). The LCDs on virtually all digital SLRs will only show the
image after it is taken and give no live previews.
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| Example
of digital compact with a twist LCD |
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Optical
Viewfinder on a Digital SLR Camera (TTL)
The optical
viewfinder of a digital SLR shows what the lens will project on
the sensor via a mirror and a prism and has therefore no
parallax error. When you depress the shutter button, the mirror
flips up so the lens can expose the sensor. As a consequence,
and due to sensor limitations, the LCD on most digital SLRs will
only show the image after it is taken and give no live previews.
In some models this is resolved by replacing the mirror by a
prism (at the expense of incoming light). The
optical viewfinder normally also features an LCD "status
bar" along the bottom of the viewfinder relaying exposure
and camera setting information.
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The
optical TTL viewfinder allows you to look "through
the lens"
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Optical
TTL viewfinder on SLR with diopter adjustment (slider on
the right side)
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Electronic
Viewfinder (EVF) on a Digital Compact Camera (TTL)
An
electronic viewfinder (EVF) functions like the LCD on a digital
compact camera and shows in real time what is projected onto the
sensor by the lens. It is basically a small LCD (typically
measuring 0.5" diagonally and 235,000 pixels) with a lens in
front of it, which allows you to frame more accurately, especially
in bright sunlight. It simulates in an electronic way the effect
of the (superior) optical TTL viewfinders found on digital SLRs
and doesn't suffer from parallax errors. Cameras
with an EVF have an LCD as well, but no true optical viewfinder.
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Example
of an electronic viewfinder
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