In some scenes there may be too much light in peripheral zones that would tend to make
the AEC under-expose a subject in the centre of the field of view and
vice versa
. The
‘Backlight Compensation’ setting tells the AEC algorithm to ignore the values of a certain
amount of pixels in the peripheral areas of the chip when doing its calculations (the higher
the setting, the more pixels are ignored). Thus a high
‘
Backlight Compensation’ value
results in relative over-exposure of the central area of the image and a zero value will
reduce exposure of the central pixels by the AEC to what it would normally do without
compensation (see figure 3.5).
Figure 3.5 Backlight Compensation factors of 0, 1 and 2 (from left to right) on an unevenly lit background
from a microscope using the AF51 in AEC mode (i.e. ‘Aperture Priority’ exposure mode).
From the above description it should be clear that changing the ‘Backlight Compensation’
setting when the camera is NOT in an automatic exposure mode will have no effect. Also
the effect of the ‘Backlight Compensation’ setting on the AEC level will vary depending on
the image currently falling on the sensor chip.
You can adjust ‘
brightness
’ and ‘
contrast
’ with the controls of those names but these
only change the post capture amplifier properties and do not increase light gathering
abilities of the chip.
OptArc AF51 Camera Page 27 of 99 User Guide v1.02
