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Specifies the operating mode of the autofocus servo. Focus modes 0 and 4 are the
only modes that should be used during routine imaging. All other focus modes are
useful for diagnosing focus problems, however, that the CSE should always leave a
customer site with fmode set to 0 or 4.
There are currently 8 focus modes. The focus modes operate as follows:
Focus mode 0 - uses lens position and optical distance data from the previous swath
Focus mode 1 - lens held in a fixed position, using "set head lpos" parameter
Focus mode 2 - stationary drum mode, uses lens position and optical distance data
from the current swath
Focus mode 3 - uses lens position and optical distance data from the current swath
Focus mode 4 - uses lens position and optical distance data from the previous swath
and the current swath, used on diffusively reflecting plates
Focus mode 5 - uses lens position and optical distance data from the previous image,
collects no data during the current image
Focus mode 6 - does not learn focus, uses lens position and optical distance data
from the current swath
Focus mode 7 - applies a linear or sinusoidal slope to the focus profile by varying
focus offset
Note that when plotting in fmode 1 the lens does not track the media, but provided
lpos is chosen properly at least part of the plate will be in focus to test imaging
without autofocus. When plotting in fmode 1 it is necessary to set a sub scan shift
of about 0.5 inches to avoid the error message "unable to learn focus, change focus
mode or shift plot".
Note that without the drum spinning and PLL on and locked only focus modes 1 and 2
can be used. For mode 2 the shutter must also be open.
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