Canon Camera Hackers Manual page 192

The signal can further be analyzed; the command returns the pulse length
in units of 10 msec. So, different functions can be encoded using different
pulse lengths.
The following script uses that functionality to allow zooming and
shooting with a simple remote control as shown in section 4.9. A short click
on the button of the remote control will fire the camera. For zooming, there
are two modes that can be selected via parameter m:
In Step mode, the remote button must be pressed longer than half a
f
second to advance the zoom to the next position. The number of posi-
tions can be set via parameter s. (For s <= 1, zooming is disabled and
any signal will fire the camera.) When the longest focal length is
reached, the zoom direction will reverse until the shortest focal length
is reached.
In Seconds mode, the remote button must be pressed longer than half a
f
second to zoom. The duration of the key press relates directly to the fo-
cal length: a longer press results in a longer focal length. The longest
duration (for the longest focal length) can be set via parameter s. (For
s <= 0, zooming is disabled and any signal will fire the camera.)
Optionally, the camera's backlight can be switched off while the script is
running (parameter b). Another option (parameter t) is to avoid the camera
powering down because of a time-out.
The script should run fine on most cameras since it automatically
adapts to the different number of zoom steps as used by different cameras:
@title USB Remote Control
@param m Zoom:0=steps,1=duration
@default m 0
@param s Steps/seconds(>1)
@default s 4
@param b Backlight:0=off,1=on
@default b 1
@param t Timeout:0=no,1=yes
@default t 0
The number of zoom steps is first stored in variable s. This number varies
for the different camera models (A-series: 9 or 15 zoom steps; S-series: 129
steps). When running in Step mode, the script first determines the current
zoom step (n) and the best zoom direction (d). The zoom speed is set to
prepare the camera for the set_zoom commands to come (section 5.5.4).
Finally, variable e is initialized for time-out control:
5.7 Example scripts
183