Basic Photography Course

CAMERA ADJUSTMENTS.

胥ach copy camera

has slightly different adjustments. You should consult
the operating manual of your copy system to learn the
proper operation and controls of your particular system.

Only the minimum basic components of a copy system
are discussed in this chapter.

GROUND GLASS FOCUSING.

胃round glass

focusing is essential for exacting copy work The image
of a document viewed on the ground glass of a copy
camera provides a means of monitoring all aspects of
the image as it will appear in the reproduction. This
includes image placement, image size, and any apparent
unwanted reflections.

BELLOWS EXTENSION.

耍 copy camera

should be capable of a bellows extension of at least two,
and preferably three times or more the focal length of
the lens being used. With a 3-inch lens and a bellows
extension of two focal lengths (6 inches) and the original
is positioned four focal lengths (12 inches) from the film

plane, a 1:1 ratio of the original size to reproduction size
is obtained. A reproduction with a 1:1 ratio can be
referred to as "life size." A bellows extension that is less
than two focal lengths cannot produce an image as large
or larger than the original. A bellows that can be

extended more than two focal lengths can produce an
image larger than the original.

LENSES FOR COPYING

A primary requirement for a lens used for copying

is that it must focus sharply across a flat plan; that is, it

must produce a sharp image over its entire field of
view-all the way out to the edges of the image. In

copying, the original has only two dimensions, and the
loss of definition at the edges of the image is much more
serious than it would be when photographing a
three-dimensional subject.

Regular camera lenses of good quality can produce

fair to good copy negatives. But most lenses for general
photography are designed to focus at a flat field for
distances greater than eight times the focal length. Since
most copy work is done at close distances, the image
field is not sharp because of the curvature of the general
lens. This effect can be compensated for by stopping
down the lens. However, because of the high degree of
diffraction at small apertures, stopping down reduces
the overall sharpness of the image. For critical copy
work, such as when copying large, detailed originals, a
lens designed for copying should be used. Such lenses,
called process lenses, produce the best image at a
lens-to-subject distance of about 10 feet or less.

8-8

Another very important aspect of a process lens is

its evenness of illumination across the focal plane.
Evenness of illumination across the entire negative is
particularly important when copying line originals. The
high-contrast films used to copy line originals have a
short exposure latitude and any falloff in illumination
results in obvious variations in exposure between the
edges and the center of the negative.

For each lens there is an optimum aperture at which

the lens produces the best image definition. For copy
work, this optimum aperture should be used whenever
possible. Since originals to be copied are flat or almost
flat, an increase in depth of field by stopping down from
the optimum aperture is not required or desired. With
some lenses, especially process lenses, the optimum
aperture and maximum aperture are the same.
Generally, however, the optimum aperture is two full
f/stops smaller than the maximum f/stop.

Most process lenses available today are apochro-

matic. They are designed to be free of chromatic
aberrations; that is, they focus sharply all three primary
colors in the same plane. Apochromatic lenses must be
used for critical work in color copying and duplication.

Since exposure times in copy work are relatively

long (i.e., seconds as compared to hundredths of a
second), a lens equipped with a means of holding the

shutter open is required. Your copy system must be

completely free of vibration to obtain sharp images. For
these long exposures, you must use the T and B settings

and a cable release.

The focal length of a lens used for copying should

be governed primarily by the size of the negative to be
produced. For example, the focal length should be about
equal to the diagonal measurement of the negative to be
made. Therefore, when you are making 35mm
negatives, use about a 1 3/4-inch or 45mm lens; a
4.5 x 6cm negatives, use a 3-inch or 75mm lens; and for
4 x 5 negatives, use a 6 1/4-inch or 160mm lens; and so
on. In any case, you should use a lens that is longer than
the film diagonal rather than a lens that is shorter. This
way, you are taking advantage of the flatter field that is
produced in the center area of the circle of illumination.
A macro lens should be used when available because it
is designed to produce sharp images at close planes.

COPYBOARD

Copyboards are an integral part of a copy system.

The function of a copyboard is to hold the original flat
and perfectly parallel to the lens and camera back When
the copyboard is not parallel, distortion results, and it

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Basic Photography Course

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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 -> CAMERA ADJUSTMENTS. 胥ach copy camera has slightly different adjustments. You should consult the operating manual of your copy system to learn the proper operation and controls of your particular system. Only the minimum basic components of a copy system are discussed in this chapter. GROUND GLASS FOCUSING. 胃round glass focusing is essential for exacting copy work The image of a document viewed on the ground glass of a copy camera provides a means of monitoring all aspects of the image as it will appear in the reproduction. This includes image placement, image size, and any apparent unwanted reflections. BELLOWS EXTENSION. 耍 copy camera should be capable of a bellows extension of at least two, and preferably three times or more the focal length of the lens being used. With a 3-inch lens and a bellows extension of two focal lengths (6 inches) and the original is positioned four focal lengths (12 inches) from the film plane, a 1:1 ratio of the original size to reproduction size is obtained. A reproduction with a 1:1 ratio can be referred to as "life size." A bellows extension that is less than two focal lengths cannot produce an image as large or larger than the original. A bellows that can be extended more than two focal lengths can produce an image larger than the original. LENSES FOR COPYING A primary requirement for a lens used for copying is that it must focus sharply across a flat plan; that is, it must produce a sharp image over its entire field of view-all the way out to the edges of the image. In copying, the original has only two dimensions, and the loss of definition at the edges of the image is much more serious than it would be when photographing a three-dimensional subject. Regular camera lenses of good quality can produce fair to good copy negatives. But most lenses for general photography are designed to focus at a flat field for distances greater than eight times the focal length. Since most copy work is done at close distances, the image field is not sharp because of the curvature of the general lens. This effect can be compensated for by stopping down the lens. However, because of the high degree of diffraction at small apertures, stopping down reduces the overall sharpness of the image. For critical copy work, such as when copying large, detailed originals, a lens designed for copying should be used. Such lenses, called process lenses, produce the best image at a lens-to-subject distance of about 10 feet or less. 8-8 Another very important aspect of a process lens is its evenness of illumination across the focal plane. Evenness of illumination across the entire negative is particularly important when copying line originals. The high-contrast films used to copy line originals have a short exposure latitude and any falloff in illumination results in obvious variations in exposure between the edges and the center of the negative. For each lens there is an optimum aperture at which the lens produces the best image definition. For copy work, this optimum aperture should be used whenever possible. Since originals to be copied are flat or almost flat, an increase in depth of field by stopping down from the optimum aperture is not required or desired. With some lenses, especially process lenses, the optimum aperture and maximum aperture are the same. Generally, however, the optimum aperture is two full f/stops smaller than the maximum f/stop. Most process lenses available today are apochro- matic. They are designed to be free of chromatic aberrations; that is, they focus sharply all three primary colors in the same plane. Apochromatic lenses must be used for critical work in color copying and duplication. Since exposure times in copy work are relatively long (i.e., seconds as compared to hundredths of a second), a lens equipped with a means of holding the shutter open is required. Your copy system must be completely free of vibration to obtain sharp images. For these long exposures, you must use the T and B settings and a cable release. The focal length of a lens used for copying should be governed primarily by the size of the negative to be produced. For example, the focal length should be about equal to the diagonal measurement of the negative to be made. Therefore, when you are making 35mm negatives, use about a 1 3/4-inch or 45mm lens; a 4.5 x 6cm negatives, use a 3-inch or 75mm lens; and for 4 x 5 negatives, use a 6 1/4-inch or 160mm lens; and so on. In any case, you should use a lens that is longer than the film diagonal rather than a lens that is shorter. This way, you are taking advantage of the flatter field that is produced in the center area of the circle of illumination. A macro lens should be used when available because it is designed to produce sharp images at close planes. COPYBOARD Copyboards are an integral part of a copy system. The function of a copyboard is to hold the original flat and perfectly parallel to the lens and camera back When the copyboard is not parallel, distortion results, and it contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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