Basic Photography Course

When a lens is focused on an object at a certain

distance, other objects, both closer and farther than the

focus distance, form larger circles of confusion. When
the film is placed at a point corresponding to the lens
focus distance, a clear image is produced (fig. 1-28).

When the film is nearer or farther away from the lens
than the corresponding lens focus distance, the image
becomes blurred because of the larger circles of

confusion caused by the intersection of light rays either
in front of, or behind, the film plane.

Table 1-3.Permissible Circle of Confusion Is Dependent on

Film Size

16mm

3 5 m m

2 1/4 x 2 3/4"

4 x 5"

8 x 10"

Film Size

0.0010

0 . 0 0 2

0.004

0.006

0.012

Diameter (inches)

Another factor affecting the circle of confusion is

lens aperture. Decreasing a lens opening narrows the
light rays passed by the lens. The narrower these rays,
the smaller the circles of confusion when the image is

not in perfect focus. In practice, this means that a small
lens opening is used to record, as clearly as possible,
several objects at varying distances. Even when the rays
from some objects do not intersect perfectly at the film

plane, the circles of confusion ahead or behind the film
are negligible and still appear as a sharp image.

The size of the permissible circle of confusion

depends on the film format size and the manner in which
the film will be used. Experience has shown that the
permissible circle of confusion should not exceed about

1/1000 of the focal length of the lens. This is normal for

the film size. The generally accepted permissible circle
of confusion diameters are given in table 1-3.

Figure 1-29.Depth of focus.

The minimum circle of confusion of most lenses is

sharp. Consequently, the distance that the focal plane

small. Thus the focal plane can be moved slightly and

can be moved forward or backward from the plane of

yet retain an acceptable sharp image. However, as the

sharp focus and continue to produce an image of

distance of the movement is increased, the circle of

acceptable sharpness is termed the depth of focus. This

confusion becomes greater and the image becomes less

depth is always within the camera (fig. 1-29).

1-24

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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 1-28.Depth of field. When a lens is focused on an object at a certain distance, other objects, both closer and farther than the focus distance, form larger circles of confusion. When the film is placed at a point corresponding to the lens focus distance, a clear image is produced (fig. 1-28). When the film is nearer or farther away from the lens than the corresponding lens focus distance, the image becomes blurred because of the larger circles of confusion caused by the intersection of light rays either in front of, or behind, the film plane. Table 1-3.Permissible Circle of Confusion Is Dependent on Film Size 16mm 3 5 m m 2 1/4 x 2 3/4" 4 x 5" 8 x 10" Film Size 0.0010 0 . 0 0 2 0.004 0.006 0.012 Diameter (inches) Another factor affecting the circle of confusion is lens aperture. Decreasing a lens opening narrows the light rays passed by the lens. The narrower these rays, the smaller the circles of confusion when the image is not in perfect focus. In practice, this means that a small lens opening is used to record, as clearly as possible, several objects at varying distances. Even when the rays from some objects do not intersect perfectly at the film plane, the circles of confusion ahead or behind the film are negligible and still appear as a sharp image. The size of the permissible circle of confusion depends on the film format size and the manner in which the film will be used. Experience has shown that the permissible circle of confusion should not exceed about 1/1000 of the focal length of the lens. This is normal for the film size. The generally accepted permissible circle of confusion diameters are given in table 1-3. Figure 1-29.Depth of focus. The minimum circle of confusion of most lenses is sharp. Consequently, the distance that the focal plane small. Thus the focal plane can be moved slightly and can be moved forward or backward from the plane of yet retain an acceptable sharp image. However, as the sharp focus and continue to produce an image of distance of the movement is increased, the circle of acceptable sharpness is termed the depth of focus. This confusion becomes greater and the image becomes less depth is always within the camera (fig. 1-29). 1-24 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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