Externally Triggering a camera Using a TTL Signal
(big edit)

&quot;Triggering TTL for on/off control of selected channels using a BNC connection Switching time &lt; 30 uS&quot;
&quot;Pulse Mode allows the user to control the integration period where the time is dictated by the duration of the pulse. If “Pulse High” mode is used, then the time the pulse is high is the time of the integration period. Vice versa for “Pulse Low” mode.&quot;

SO you have the choice of positive edge or negative edge, or positive duration or negative duration  somewhere in software.
You only want the camera to start capturing before the flash goes.
But we do not know the flash delay time. It is probably a few to 10 microseconds, based on my experience. You can determine this by asking them or testing it with a fast light sensor (e.g. Photo diode biased and 50 Ohm to scope.)
The xenon flash time of 1ns is not critical about the capture duration AS LONG AS IT IS TRIGGERED BEFORE the flash actually occurs.
However the trigger delay time may be critical as we do not know the setup and delay times for each device to be triggered and I did not find an explicit spec for this. We call this a &quot;Race condition&quot; when two events are triggered and you want the camera to capture the output of the flash.
IN logic design it usually works the other way around. We use a Flip Flop or memory cell to capture the data before it changes on a clock edge.  ... and not after some delay when a 1ns flash occurs.  THe Xenon flash works by a secondary emission arc of a capacitor discharge, so once ionization starts which can take a few us, it completes in a hyper abrupt &quot;tunneling mode&quot; in 1ns arcing across the inner gas.  It also causes really huge EMI pulses everywhere if done at a fast repetitive rate and can interfere with cell phone reception. ( like Safety Xenon Bulbs flashes at 2 pulse/sec. are notorious for wireless interference)
( I finally discovered all the options on your camera to indicate either polarity or edge can be used on your camera)
By using a slow ramp signal generator 0 to 5V or power supply you can carefully measure the threshold for edge trigger on each device to understand where it triggers.  I am not 100% sure they are TTL compatible precisely as TTL is strictly defined with a threshold of 1.5V or more likely it is CMOS with 2.5V threshold which can be TTL compatible but does not work when you load both devices from your generator.
This means your generator is poorly matched to your 2 loads Normally TTL can drive 10 loads or more and this does not seem to be the case.
You can make a quick fix by adding 330 to 470 Ohm pullup to the TTL signal generator nearby to 5V and connect grounds together so that you get 0.5 to 5V output swing or adjust as necessary.
Once you have verified trigger to both devices successfully, then it may work. Otherwise Sync delay on flash may be needed if it triggers to fast.
Again sorry for not reading your manual thoroughly as you...( ought to have)
&quot;Simple&quot; possible solution



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