Figure 3.4 Example of the effect of the ‘Power Line Frequency’ settings (shown in yellow text at the top left
of each image). The photographs were taken with the AF51 on a Leica DMLS microscope equipped with its
original AC filament bulb operating on a 50Hz AC mains supply. The image is contrast enhanced to
exaggerate the effect for the purposes of illustration.
The reduction in horizontal line fluctuations is best seen in live images. Still images taken
with any of these settings may still show residual sinusoidal fluctuation.
Residual
fluctuations can be reduced or eliminated by using multi-frame averaging (see
software options later in this manual) or a longer exposure setting in the camera
(see below).
Note that it is ineffective to change this setting from value 2 (60 Hz) directly to value 0
(off). You need to change from 2 to 1 to 0. Going the other way does not matter (you can
change from 0 directly to 3). The reason for this behaviour is that the ‘off’ (0) setting for
this control simply leaves the setting where it was last – it is effectively non-functional.
The ‘
Backlight Compensation
’ feature affects the behaviour of the automatic exposure
level when the automatic exposure control (AEC) is enabled (automatic exposure settings
are discussed below in the section on the ‘Camera Controls’).
The AEC algorithm samples pixel values from target areas across the chip and attempts
to increase or decrease the exposure of the chip to avoid saturation of pixels while using
the maximum dynamic range of pixel values for the image. If the image is too brightly lit
tending to cause saturation it will reduce exposure till there are no saturated pixels in its
target reference areas. Conversely if the pixels in the target areas are too dark it will
increase exposure. In this way the AEC attempts to use a maximal amount of the pixel
value range for the image without over or under-exposing the scene.
OptArc AF51 Camera Page 26 of 99 User Guide v1.02
