Choosing the Right Camera Focal Length
Changing lenses is like looking at the landscape through different
windows.
-
A standard lens, usually refer to fixed
lens with 50mm in focal length - gives a view of the scene that
approximates to human vision and is consequently often referred to as a
normal lens.
-
The wide-angle lens is the landscape
photographer's picture window, recording on film a broad swathe of the
scene.
-
Telephoto lenses are like cottage windows
- distant details easily fill the frame.
Choosing the right lens isn't just about
fitting everything into the picture, though, because focal length
affects the image in other ways. One of these is depth of field.
Depth of field
Long focal length lenses reduce depth of field, so that less of the
landscape is in focus on film; wide-angle lenses keep more of the image
sharp. So if you want to isolate just a portion of the scene, and throw
other subject planes out of focus, use a telephoto lens, or a "tele"
setting on a zoom lens. For maximum sharpness, select the smallest
aperture.
Viewpoints
Different lenses give you a wider choice of viewpoints, and this in
turn affects the appearance of the picture. If you use a telephoto
lens, you'll need to back away from the subject to fit everything in,
and the distant viewpoint tends to flatten perspective. With a
wide-angle lens, you can picture the same subject from a close
viewpoint. Things near to the camera seem proportionately bigger, and
the background seems to recede.
Angle of view and focal length
In theory, focal length is the distance between two points in the lens,
but in practice, it is a quick way to specify angle of view.
-
Most wide-angle lenses have focal lengths
ranging from 13mm to 35mm, and fields of view from 118 degree to 62
degree.
-
50mm standard lenses take in 46 degree
across the diagonal of the frame.
-
Telephoto lenses, ranging from 85mm to
200mm, have fields of view from 16 degree to 1 degree.
|
