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Operation of the Camera 135
External TC, Time of day
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Use: This format is often used on multi-camera productions with sync-sound.
When all cameras are running at sync-sound speed, which is also the project
frame rate, sound and image time code match and allow for easy syncing in post.
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Setup: The sound department acts as the timecode master, and generates
timecode which uses the time of day as a value, and a time base matching the
project frame rate. Twenty-four hours of time will translate into twenty-four hours of
time code.
Timecode is fed to the camera via the TC connector. The timecode source must
be set in the camera to Ext LTC and the mode to Free Run. The project fps setting
must match both the sensor frame rate and the time base of the external timecode
signal. The camera can be set to use Jam sync generator, in which it samples the
timecode value once and then continues counting based on its own high-precision
crystal clock. The timecode source can be disconnected from the camera after
jamming in Jam sync generator mode. This mode ensures stable timecode with an
offset of less than one frame for each eight hours, after which the camera has to
be re-jammed.
Alternatively, the camera can be set to regenerate mode, or Regen on the
TIMECODE OPTIONS screen. In Regen mode, the camera uses the timecode
value of the external timecode source. This ensures correct timecode for an infinite
duration, but the timecode source must remain connected to the camera. Note that
the camera ignores external timecode during record and counts using its internal
clock to avoid timecode jumps should connection problems arise, e. g. due to a
faulty timecode cable.
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Variations: If shooting starts close to midnight, the timecode might be started with
an offset time of day to prevent a rollover at midnight.
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Restrictions: External timecode is only possible if the camera is running at sync-
sound speed. If the camera is over- or under-cranking, the timecode frame rate
will no longer match the sensor framerate, and timecode values would either be
duplicate or dropped. To prevent this, the ALEXA will automatically switch to Int TC
source and Regen mode when the sensor frame rate is changed.
Internal TC, Rec Run
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Use: Record run timecode is often used on single camera productions that are
either MOS or use a dumb slate to sync picture and sound. Record run timecode
guarantees continuous timecode on all recorded data. Record runtime code also
works with over- and under-cranking.
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Setup: The timecode source must be set to Int TC, the mode to Rec Run and the
generator to Regen. Timecode counts up only during recording, by one frame for
each image generated by the sensor. The timecode counts at the project frame
rate set on the camera. Normally, the timecode hour value advances by one hour
for each new reel, using only hours 01-20 for reel 1-20, and then restarting at hour
01 for reel 21.
•
Variations: Record run timecode might be used for off-speed work on productions
that use external timecode sources for all sync sound.
•
Restrictions: None.
14.4 Syncing the Sensors of Two Cameras
Two ALEXAs can be synced for 3D applications or any application requiring sensor
sync using the EXT connectors and corresponding cable. When synced, images are
captured from each camera's sensor at precisely the same time.
NOTICE
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Syncing two sensors is possible at frame rates of at least 1.000 fps.
•
Use both sensor sync and settings sync (see next chapter) in 3D setups.
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