Basic Photography Course

closely resembles the central vision coverage of the
human eye. Wide-angle lenses have a large or wide

angle of field Long focal-length lenses (often called
telephotolenses) have a narrow angle of field (fig. 1-21).

Angle of

View.

Angle of view determines the

coverage of a lens with a particular size of film, with the
lens-to-film distance remaining unchanged. Angle of
view is an angle with the intercept point at the lens and
its sides matching the corners of the film.

The angle of view (fig. 1-22) of a normal focal-

length lens with a given film size can approach but never
exceed the angle of field of the lens. Any lens recording

an angle greater than 55 degrees with a given film size
has a short-focal length and is called a wide-angle lens.
Any lens with an angle of view less than 45 degrees with
a given film size has a longer focal length.

Lens Diaphragm

The diaphragm of a lens is an opening in the lens

that allows light to pass through it to expose the film (or
other recording medium). This opening can be made
larger or smaller to allow more or less light to pass
through the lens. When the diaphragm opening is very

Figure 1-22.Angle of view.

large, only the object that the lens is focused on is in
sharp focus. As the diaphragm opening is reduced (made

smaller), more objects in a scene, both in front and
behind the point of focus become sharper. The lens
diaphragm is used in conjunction with the shutter of
the camera to control the amount of light to expose
the film.

PERSPECTIVE

The human eyes see objects in three dimensions, but

a lens reproduces a view in two dimensions. The missing
dimension, depth, is suggested by the relative size and
position of the various objects in a picture. Perspective,
which is the relationship of objects in a photograph,
affects the naturalness of a picture. Good perspective
represents objects as they actually appear to human
eyes.

Since wide-angle lenses take in a greater area, most

photographers use them to photograph in tight quarters.

And they use long-focus (long focal length) lenses to

bring distant objects closer. This is fine, but it is only
part of the story. Lenses of different focal length are also
used to control perspective.

Perspective is NOT dependent on the focal length

of the lens. It is a function of camera-to-subject distance.
But a choice of lenses of a different focal length does
enable you to get the desired image size at the selected
distance for best perspective. For example, suppose you
come across a placid farm scene. A rustic rail fence is in
the foreground, and a cow is munching on a haystack in
the field. The cow and her lunch are 100 feet behind the

fence; you are 10 feet in front of the fence. The fence is
essential to your picture and you use a 50mm lens. The
result! The cow is 110 feet from the camera and is too
small in relation to the fence. Your picture is a flop. Now
change your perspective. Back up 40 feet from the fence

1-17

contents

Basic Photography Course

<- previous page

next page ->


DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> Figure 1-21.Angle of field. closely resembles the central vision coverage of the human eye. Wide-angle lenses have a large or wide angle of field Long focal-length lenses (often called telephotolenses) have a narrow angle of field (fig. 1-21). Angle of View. Angle of view determines the coverage of a lens with a particular size of film, with the lens-to-film distance remaining unchanged. Angle of view is an angle with the intercept point at the lens and its sides matching the corners of the film. The angle of view (fig. 1-22) of a normal focal- length lens with a given film size can approach but never exceed the angle of field of the lens. Any lens recording an angle greater than 55 degrees with a given film size has a short-focal length and is called a wide-angle lens. Any lens with an angle of view less than 45 degrees with a given film size has a longer focal length. Lens Diaphragm The diaphragm of a lens is an opening in the lens that allows light to pass through it to expose the film (or other recording medium). This opening can be made larger or smaller to allow more or less light to pass through the lens. When the diaphragm opening is very Figure 1-22.Angle of view. large, only the object that the lens is focused on is in sharp focus. As the diaphragm opening is reduced (made smaller), more objects in a scene, both in front and behind the point of focus become sharper. The lens diaphragm is used in conjunction with the shutter of the camera to control the amount of light to expose the film. PERSPECTIVE The human eyes see objects in three dimensions, but a lens reproduces a view in two dimensions. The missing dimension, depth, is suggested by the relative size and position of the various objects in a picture. Perspective, which is the relationship of objects in a photograph, affects the naturalness of a picture. Good perspective represents objects as they actually appear to human eyes. Since wide-angle lenses take in a greater area, most photographers use them to photograph in tight quarters. And they use long-focus (long focal length) lenses to bring distant objects closer. This is fine, but it is only part of the story. Lenses of different focal length are also used to control perspective. Perspective is NOT dependent on the focal length of the lens. It is a function of camera-to-subject distance. But a choice of lenses of a different focal length does enable you to get the desired image size at the selected distance for best perspective. For example, suppose you come across a placid farm scene. A rustic rail fence is in the foreground, and a cow is munching on a haystack in the field. The cow and her lunch are 100 feet behind the fence; you are 10 feet in front of the fence. The fence is essential to your picture and you use a 50mm lens. The result! The cow is 110 feet from the camera and is too small in relation to the fence. Your picture is a flop. Now change your perspective. Back up 40 feet from the fence 1-17 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
	WWW.DOFMASTER.COM © 2006 Don Fleming. All rights reserved.