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Two cameras timelapse with only optional shutter release

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Offline Sasha

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Two cameras timelapse with only optional shutter release
« on: 14 / December / 2008, 14:05:15 »
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I like to shoot a stereo photo with two Canon S5 IS with a base line (distance between the cameras) of several meters.
These could be 10 to 20 meters or even more. So wiring is not an option.

This is my idea:

On both cameras a script is running that get it's initial starting moment from the button of
an USB remote switch made for SDM. Now the scripts are waiting in intervals of - let's say - 15 sec each
while the cameras are placed on different tripods in a distance to each other.
A counter on the display shows the time left of the interval.
After an interval has ended, a new one starts immediately.

If I press a certain control button on the camera, nothing happens at first. But at the end
of the interval, a photo is shot. If I can manage to release the other camera before
the end of the same interval, I get a synchronised stereo shot, without directly
wiring both cameras.
The result may be similiar to this:

Would a mentionable time lag occur after several intervals?
Asynchrony of a few milliseconds wouldn't bother me.
Can Chdk read out the cameras internal timer?
The script could then get it's timing after each interval from the system clock.

Can anybody please elaborate whether this is possible or not?
I'm an eager script writer!  :xmas

Best regards!
Sasha
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Offline fudgey

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Re: Two cameras timelapse with only optional shutter release
« Reply #1 on: 14 / December / 2008, 14:59:00 »
20 m or more is not a problem with wires or powerful IR remotes.

That said, the camera's internal clock is accessible in ubasic and lua with the get_tick_count command with 10 ms resolution and also some date/time functions (like os.date in Lua) with (I think) 1 s resolution.

Once you get the two cameras in sync (with get_tick_count), the drift shouldn't be significant unless the timelapse is long (if the clocks drift apart 1 sec per year, it builds up to 11 ms in four days).

Remember that you must sync the press shoot_full command, not shoot(), otherwise exposure related things will make your sync way worse.
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