A viewfinder, separate from the ubiquitous LCD screen, offers a number
of advantages. First and foremost, it relieves the batteries of the
camera from the heavy drain of the LCD screen; and can considerably
increase their life.
Second, it provides a useful alternative to the LCD screen outdoors.
LCD screens generally require a backlight to be visible and this light
can easily be overwhelmed by sunlight, making it impossible to see the
image. Alternatives exist, such as screens that let the sunlight go through
and to reflect it back through the image (Sony's DSC-F505 for example);
or others that funnel the light through a top opening, and channel it
back through the screen. These alternatives help, but both the colour
rendition and contrast of image, is lower than it would be when the backlight
is used.
Separate viewfinders do not have these problems, but they do have others
which will be detailed later. Viewfinders come in 3 basic types:
Separate from the lens, commonly referred to as an
optical viewfinder
Through The Lens, commonly referred to as a TTL viewfinder,
Electronic Viewfinder, also called an Eye-level LCD
viewfinder.
The Optical Viewfinder:
Whether the camera's lens is a zoom or not, the viewfinder is separate
from the lens and mimics the view and focal length of the lens.
The size of the exit pupil of a viewfinder dictates how clear the image
will be, and a relatively large exit pupil is important if eyeglasses are
worn since they move the eye back from the viewfinder. A viewfinder equipped
with a diopter correction can correct vision and avoid the use of glasses
when taking photos. But, the correction only works with near, or far-sightedness.
All optical viewfinder
are placed as close to the lens as possible to lessen the
Parallax error.
Parallax error occurs because the lens of the camera and the viewfinder
see the subject from a slightly different position. Over a long distance
the error is hard to detect; but over short distances, such as when photographing
portraits or macros, the difference in the perspective becomes magnified
and can enormously affect the composition of a photo. This is why many
digital cameras compensate by turning on the LCD screen when the macro
function is used. The screen shows the image the sensor is receiving and
avoids the parallax error.
Parallax has always been a problem with separate optical
viewfinders, and many ideas have been used to minimize it.
Optical viewfinders will generally have "crop" or "parallax" markings,
indicating the actual image-taking area, but none of these
simpler methods are 100% effective. Additionally, optical
viewfinders cannot display 100% of the image that will be
captured and are commonly limited to around 85% or less of
the actual frame. This is why TTL (through the lens) viewfinders
were developed.
The Optical TTL Viewfinder:
These are generally used with more expensive cameras, and present the image
the lens receives.
The different systems used to show the image originating from the lens
vary in their details, but they generally reflect, or split, the light
coming through the lens and direct some, or all of it to the viewfinder
while the image is being composed.
The disadvantage of TTL viewfinders is that they are more
expensive to build because of their complexity. This is why
they are more commonly found on high-end and professional
digital cameras. Furthermore, they commonly require a small
LCD display to indicate focusing and exposure, adding to
their cost. However, this may be changing. Hewlett-Packard,
working in cooperation with Pentax, recently released a camera
(HP 912/Pentax EI2000) which uses a TTL viewfinder, but is
quite reasonably priced.
Recently, some digital cameras have arrived on the market which use a variation
of the TTL viewfinder, but forgo the complex optical systems. Instead,
they use viewfinders similar to those found on video cameras: tiny LCD
screens which show the same view and information as the main LCD screen,
but in the shelter of a viewfinder.
The Electronic Viewfinder:
The advantages of this type of viewfinder are the same as for the optical
version: they show exactly what will be captured, they are visible in daylight
(by virtue of being recessed behind an eyecup), indicate aperture, shutter
speed, etc. but, in addition, they can also display the camera menus—something
optical viewfinders cannot do.
The disadvantages of electronic viewfinders can be summarized
in 3 points: they require power (unlike the optical, or optical
TTL viewfinders); show an overly bright view, just like LCD
screens; and are quite coarse in comparison to optical systems.
The latter point may be of greater importance since these
systems—to date—are unable to show the smaller
details in the frame: for instance whether someone's eyes
are open, or partially closed.
While no system is "perfect", the general consensus is that of
all three the optical TTL viewfinder is still the best.
