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Focus Options
- Fixed Focus: Fixed focus is usually found in consumer
level, lower priced cameras. A specific range of area is selected
by the camera manufacturer to serve for the camera's focus. The
range may be 5 feet and beyond for which the focus is fixed and
cannot be altered.
- Manual Focus: a manual focus allows the user to adjust
the lens to create the desired sharpness for both the foreground
and background of the subject matter.
- Auto Focus: A selected area in the center of the
lens is used as the target area around which the image is focused.
When the subject is centered in the viewfinder, the auto focus adjusts
the image clarity for the shot. If the auto focus cannot be manually
altered, a user will be unable to sharply focus all aspects of the
subject, especially if the subject is not centered in the focus.
- Dynamic Focus: Dynamic focus allows for the selection
of focus positions that are not necessarily centered but may be
to the right or left of the center of the viewfinder. With dynamic
focus feature, the subject can be placed out of the center of the
picture and yet remain in focus.
- Tracked Focus: Tracked focus is a feature that holds
a subject in focus while the subject is in motion. The camera automatically
tracks the speed and anticipates the direction of the subject's
movement. The camera then adjusts the focus automatically for the
action shot.
Exposure Options
If no manual intervention occurs, exposures can
also be controlled automatically as the camera's internal light meter
measures the amount of light reflected from the subject matter and
surrounding area. The camera will then either digitally display the
proper aperture and shutter speed setting so the user can make the
adjustments, or the camera makes one of the adjustments but not the
other, or all of the adjustments are made with fully automatic processes.
- Aperture Priority: Apeture Priority refers to the
feature that will enable the user to control the depth of field
or the clarity of the background by selecting the aperture setting.
The shutter speed is then automatically set in accordance with the
aperture setting to provide the best exposure.
- Shutter Priority: The shutter priority refers to
the feature that will enable the user to control the shutter speed,
keeping it open for longer exposures or closing it quickly to capture
moving action. The aperture is then automatically set by the camera
for the best exposure.
- Fully Automatic: Fully automatic refers to the feature
that will set both the aperture and the shutter speed for the best
exposure.
Focus and Exposure Locking
As the picture is taken, it is usually best to partially
depress the shutter button to give the camera time to adjust (length
of time varies on camera models) the exposure and focus settings.
Shutter speeds can range from 30 seconds to 1/10000 of a second. Once
the settings are locked in place, the user can then finish depressing
the shutter to take the photo.
During the delay between pressing the shutter release
and taking the picture, the camera performs a number of electronic
tasks. It clears the CCD, corrects the white balance, meters and sets
the exposure, focuses the image, and finally fires the flash (if needed)
and then takes the picture. The camera then compresses the image and
saves it in memory. Then, another picture cannot be taken until the
camera completes the compression process, which may create a delay
depending on the camera's processing speeds.
Light Sensing and Metering
For cameras using film, there are different types
of film material available to provide the best color reproduction
in specific lighting conditions. Since digital cameras do not use
film, varying lighting conditions are controlled by the camera's exposure
system instead of through the use of different film. It is important
to understand the camera's exposure system in order to make sure the
camera's lighting sensor is capable of handling a variety of lighting
conditions that will be encountered.
- By checking the camera's "equivalent ISO number", which
is a measurement of the sensitivity of the lighting sensor to varying
lighting conditions, images can be improved when taken in different
levels of light.
- The higher the ISO number, the better the image in low light and
conversely, the lower the ISO number, the better the image in high
or intense lighting.
- ISO sensitivity settings can range from 200 to 800 on consumer
level cameras and above 1000 on professional level models.
- Additional options for improving image quality can be provided
with cameras having a wide range of shutter speeds and lens apertures.
- Check the number of modes available on the camera's internal or
external flash and its distance range. This feature can be used
to increase the lighting of objects within close range.
Lighting conditions are affected by two distinct factors: the quality
of the light and the quantity of light. Insufficient light results
in underexposure while excessive amounts of light will overexpose
the image. To measure the light and make the proper adjustment for
the proper exposure, digital cameras are equipped with metering systems
to properly set the exposure. Metering systems include the following:
- Spot or Partial Metering: Light is measured in a
small circular area around the center of the image. Spot metering
will typically measure less than 4% of the image and partial metering
will measure almost 10% of the image. Spot and partial metering
is used most often for close-up photography or when there is a significant
difference between the brightness of the foreground and the background.
- Bottom-Weighted Metering: The light is measured by
averaging the tonal values around the lower half of the picture
setting and adjusting to a middle gray value to create the proper
exposure.
- Center-Weighted Metering: The light is measured by
averaging the tonal values around the center of the subject matter
and adjusting to a middle gray value in order to create the proper
exposure. Most often the metering will measure 75% of the center
of the image and 25% of the outer area. Center-weighted metering
is used most often when the subject matter fills a majority of the
space in the image area.
- Matrix or Multi-Zone Metering: A metering process
which electronically analyzes data regarding brightness, contrast,
distance, and focus in order to adjust exposures to provide improved
accuracy for color reproduction.
Exposure Correction
Auto exposure systems can become unreliable in some
settings where extreme brightness (direct sun and reflections on water)
or very low light can cause the automatic features to over compensate
for the measured light. To override the automatic exposure controls,
some digital cameras have an exposure correction feature (+/- EV compensation)
which can be used for manual settings that are required in low-light
situations. With exposure correction or compensation, the camera can
be set to allow more or less light, depending on the required setting.
For someone who does not have much experience with correcting for
low light or bright light situations, some cameras have an image display
feature allowing the user to see the effect on the image as the settings
are manually controlled.
White Balance
Light coming through the lens needs to be balanced
in order to achieve natural or accurate coloration. Colors differ
under various lighting conditions. Some colors appear brighter while
others appear dull in the same setting. Cameras using roll film adjust
for color conditions (interior, outdoors, bright sun, etc.) with different
types of film or by using lens filters. On digital cameras, color
adjustment occurs through the use of white balance adjustments. Proper
white balance is achieved by extracting white light from the light
that comes through the lens. By adjusting the white light in a setting
to compensate for the ambient lighting, all of the colors that make
up white light (the additive primaries red, green, and blue) are adjusted
accordingly.
Tone Compensation
To insure that natural tones are reproduced accurately,
some digital cameras provide a tone adjustment or tone curve control,
which compensates for the brightness and contrast of the subject matter.
The tone curve control feature determines the optimal tone curve for
natural coloration and natural tones in order to produce the highest
quality image possible under the lighting conditions of the setting.
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