150 CHAPTER 5 Scripting
Scheduled operation
The following script implements a quite different time machine. Instead of
accepting a few parameters and taking photos in equal intervals, it allows
for far more complex actions; it reads a schedule from a predefined text file
and processes that schedule.
This has advantages: you can describe a far more complex time series
than what is possible with a few parameters. There are disadvantages, too:
before using the script, you must create a schedule file on the PC. Later
changes in the field are not possible. To provide for some flexibility, I imple-
mented the option to select among different schedule files. All schedule
files are expected to be in folder CHDK/SCHED/. When you start the script,
you can scroll through the content of that folder and select the schedule
you wish to execute.
Each schedule file is created as a simple text file. Each line in the text
describes a different time series. After a time series has stopped, the next
line is executed. When there are no more lines left, the script stops. This is
the syntax of a single line:
[F/A/I/mm ]met[ n i1[-i2]][I/N/D]
Let’s examine what that means. The first clause is optional (denoted by the
brackets) and specifies the focusing mode. Cameras with a manual focus
option must be set manually to manual focus to allow for the options of
that clause. The following values are possible:
f
F causes the camera to determine the subject distance immediately
and then lock the focus, so the autofocus is switched off during the
subsequent shots.
f
A removes the focus lock and allows the camera to autofocus again with
each new shot.
f
I sets the focus to infinity.
f
mm sets the camera to the specified subject distance (in mm).
Next comes met, the Mission Elapsed Time. This entry defines when the se-
ries begins, measured from the time when the script was started. It is given
in the format [[h:]m:]s. Seconds must be defined, but minutes and hours
are optional.
The following clause is optional. In the case of a single shot, it can be
omitted. In the case of a time series, n defines the number of shots. i1
specifies the interval between the shots. Again, intervals are specified in
the [[h:]m:]s format. Optionally, a second interval i2 can be specified af-
ter a dash. If so, we have a sliding interval starting at i1 and gradually
changing to i2 with each shot. This allows for accelerating and decelerat-
ing the time series—an interesting option for time-lapse movies.
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