Basic Photography Course

Exposure Compensation for Bellows Extension

As discussed in chapter 4, an exposure calculated

with an exposure meter is precise only for a lens set at
a distance equal to one focal length When the distance
between the optical center of the lens and the focal plane
is greater than one focal length, an increase to the
indicated exposure is usually required. Before an
accurate increase in exposure can be applied by opening
the lens diaphragm, the effectiveness of the f/stop of the
indicated exposure should be determined Remember,
the marked f/stops of a lens that is set beyond one focal
length are not valid because the f/stops are a ratio of the
diameter of the lens aperture to one focal length. Refer
to chapter 4 to determine how to compensate exposure

for bellows extension.

PROCESSING COPY FILMS

Films used for copying are processed the same as

any other film. They can be processed by machine or by
hand, using tanks or trays. Recommendations for
specific developers, developing times, and developing
temperatures are given with each type of film. Some
films not designed specifically for copying may yield
negatives with excessive contrast. This can usually be
avoided by reducing the developing time. Consult the
Photo-Lab Index to find suitable developing times to
lower or raise contrast.

CATHODE-RAY TUBES

Although taking photographic images from

cathode-ray tubes (CRT) is not actually a type of copy
work, it has become more commonplace to photograph

their images for briefs and presentations. Televisions,
computer monitors, and radarscopes all can be classified

as CRT photography.

When you are shooting CRTs, like all copy

photography, it is important for the optical axis of the
lens to be centered and perpendicular to the monitor. The
camera must be mounted on a sturdy tripod. A cable
release and a macro lens are recommended.

When you are photographing radarscopes, time or

shutter speed is not a factor of exposure. The number of
sweeps on the scope is the factor that determines the
exposure at a given f/stop. The number of rotations is
not proportional to film exposure. As a general rule, the
exposure doubles between one and three sweeps. To get
the correct exposure, you must bracket the exposure. A
good starting point for less than three sweeps with ISO

125 film is at f/5.6.

To get the sharpest and clearest image possible, you

must adjust the brightness of the radarscope correctly.
Do this by turning up the intensity until halos appear.
Then turn it down until the halos just disappear. When
the intensity of the scope is too great, the image appears
out of focus. If the intensity of the scope is not great
enough, there is little contrast between the video and the
background.

Computer-generated graphics are a common means

of producing material for use in slide briefings. When
available, use a computer monitor with a flat screen
rather than a curved screen Use the same procedures for
shooting computer screens that you use for radarscopes.
The difference is there is no sweeping motion when
shooting a computer monitor or a television. When
motion is apparent, you must use a shutter speed of

1/30th of a second. When you use this shutter speed, the

film records the image without obvious scan lines and
stops the motion of the image.

When photographing images from a CRT, always

darken the room before you make the exposures. This
prevents glare on the screen and only the illumination
from the screen affects the film.

SLIDE DUPLICATING

In photography, you must often make duplicate

slides from an original. Duplicating is actually a form of
copying. A duplicate or "dupe" can be made to almost
any desired size. Contrast and density along with color
adjustments can be made when duplicating color slides.

Color slides are duped to provide extra copies of the

slide, correct color balance and contrast errors, or even
to change or enhance colors for special applications.

CAMERAS AND ACCESSORIES FOR
DUPLICATING

Except for the copyboard or easel, the features of

the equipment used for duplicating transparent originals

are essentially the same as that used in copying

reflection originals. The exception being that the
copyboard for copying transparent originals must allow
light to be transmitted through the original to the camera.

Except for being lit by transmitted light, large

format transparent originals (larger than 35mm) are
copied the same as reflection originals. 35mm
transparencies are copied with special slide copying
attachments for cameras, or copied in specially
designed, semiautomatic or automatic slide copiers.

8-17

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 -> Exposure Compensation for Bellows Extension As discussed in chapter 4, an exposure calculated with an exposure meter is precise only for a lens set at a distance equal to one focal length When the distance between the optical center of the lens and the focal plane is greater than one focal length, an increase to the indicated exposure is usually required. Before an accurate increase in exposure can be applied by opening the lens diaphragm, the effectiveness of the f/stop of the indicated exposure should be determined Remember, the marked f/stops of a lens that is set beyond one focal length are not valid because the f/stops are a ratio of the diameter of the lens aperture to one focal length. Refer to chapter 4 to determine how to compensate exposure for bellows extension. PROCESSING COPY FILMS Films used for copying are processed the same as any other film. They can be processed by machine or by hand, using tanks or trays. Recommendations for specific developers, developing times, and developing temperatures are given with each type of film. Some films not designed specifically for copying may yield negatives with excessive contrast. This can usually be avoided by reducing the developing time. Consult the Photo-Lab Index to find suitable developing times to lower or raise contrast. CATHODE-RAY TUBES Although taking photographic images from cathode-ray tubes (CRT) is not actually a type of copy work, it has become more commonplace to photograph their images for briefs and presentations. Televisions, computer monitors, and radarscopes all can be classified as CRT photography. When you are shooting CRTs, like all copy photography, it is important for the optical axis of the lens to be centered and perpendicular to the monitor. The camera must be mounted on a sturdy tripod. A cable release and a macro lens are recommended. When you are photographing radarscopes, time or shutter speed is not a factor of exposure. The number of sweeps on the scope is the factor that determines the exposure at a given f/stop. The number of rotations is not proportional to film exposure. As a general rule, the exposure doubles between one and three sweeps. To get the correct exposure, you must bracket the exposure. A good starting point for less than three sweeps with ISO 125 film is at f/5.6. To get the sharpest and clearest image possible, you must adjust the brightness of the radarscope correctly. Do this by turning up the intensity until halos appear. Then turn it down until the halos just disappear. When the intensity of the scope is too great, the image appears out of focus. If the intensity of the scope is not great enough, there is little contrast between the video and the background. Computer-generated graphics are a common means of producing material for use in slide briefings. When available, use a computer monitor with a flat screen rather than a curved screen Use the same procedures for shooting computer screens that you use for radarscopes. The difference is there is no sweeping motion when shooting a computer monitor or a television. When motion is apparent, you must use a shutter speed of 1/30th of a second. When you use this shutter speed, the film records the image without obvious scan lines and stops the motion of the image. When photographing images from a CRT, always darken the room before you make the exposures. This prevents glare on the screen and only the illumination from the screen affects the film. SLIDE DUPLICATING In photography, you must often make duplicate slides from an original. Duplicating is actually a form of copying. A duplicate or "dupe" can be made to almost any desired size. Contrast and density along with color adjustments can be made when duplicating color slides. Color slides are duped to provide extra copies of the slide, correct color balance and contrast errors, or even to change or enhance colors for special applications. CAMERAS AND ACCESSORIES FOR DUPLICATING Except for the copyboard or easel, the features of the equipment used for duplicating transparent originals are essentially the same as that used in copying reflection originals. The exception being that the copyboard for copying transparent originals must allow light to be transmitted through the original to the camera. Except for being lit by transmitted light, large format transparent originals (larger than 35mm) are copied the same as reflection originals. 35mm transparencies are copied with special slide copying attachments for cameras, or copied in specially designed, semiautomatic or automatic slide copiers. 8-17 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.