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Auto Exposure ON/OFF and Exposure Control
Auto Exposure
is switched ON or OFF via the control menu.
•
Switch auto exposure
OFF
to control exposure time directly in imaging mode. Auto exposure OFF is
recommended for most night vision applications because exposure time control at night is used primarily to select
the best trade-off between motion blur, image update rate and image quality. Use the AUTO gain setting when
auto exposure is off, so that the image will always be displayed at the best brightness.
•
When auto exposure is
ON
, the exposure control will adjust the
exposure target
while the camera sets the
exposure time to meet the target. The
exposure target
defines the average ‘fill level’ of the pixels. The exposure
target is displayed as a green line in the histogram graph (see Basic Operations). An exposure target of 50%
(green line in the middle of the graph) provides least image noise but results in the longest exposure time. Move
the line further to the left to reduce the exposure time for a given scene. This results in less motion blur, but the
image will start exhibiting noise if AUTO gain is selected or become darker if a fixed gain is selected. Auto
Exposure
ON
is recommended for most daytime or bright light imaging. Auto exposure limits exposure time to no
more than 1/35 second in order to keep motion blur under control. Switch auto exposure
OFF
when longer
exposure times are needed.
Aperture Control
Aperture is one of the three
Active Controls
on the status menu. Electronic aperture control is available for most Canon
and compatible lenses, but not for the FL-400 lens. A greater F/ number means the lens aperture is more restricted and
less light falls on the sensor. A smaller F/ number means the lens aperture is wider open and more light falls on the
sensor. Open the aperture all the way for most night applications. During daytime, opt to close the aperture to about F/8
to obtain the sharpest image or to widen the distance range that is in focus (greater depth of field). When using the night
vision sensor at day time, the image will have better contrast when the aperture is closed sufficiently so that exposure
times of 1/1000 sec or more can be used.
Use of the Histogram Display
The histogram display at the center of the status bar is available to optimize the information in the captured image,
ensuring in both dark and bright portions of a scene. There are three pieces of information.
Histogram Display
•
The histogram is a gray shaded band indicating the number of pixels at each level of brightness. The spectrum
goes from black pixels (left) to white pixels (right). The more pixels fall into a given level of brightness, the
brighter the histogram will be at that spot. If a white line or band appears at the very right (example above), then
some pixels are completely full and information is lost in bright parts of the scene: reduce exposure time or target.
If a white line or band appears at the very left, then some pixels are almost empty and information is lost in dark
parts of the scene: increase the exposure time or target.
•
The green line is the exposure target. When Auto Exposure is ON the exposure control will move this line left or
right. Move the green line left to a lower average pixel fill level and smaller exposure time, or right for a greater
average pixel fill level and greater exposure time.
•
The white line is the average exposure of the scene. When Auto Exposure is ON the camera will change the
exposure time until the white line matches the green line.
