Here's an update for the last post.
Two 74HC86 XOR gates have been added to be able to invert the input and output polarities.

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3300&stc=1&d=123889536 2" /><!-- Name: ZeroDelay3.GIF Views: 1067 Size: 14.1 KB -->

I see that you specified "Trigger input is TTL 5V rising or falling edge, selectable." in the first post.
I must have missed that part.

I could be diverging from what you want to do.
But the problem is intriguing, so I'm continuing onward ... thru the Fog.

I think the circuit above gives you all the capabilities you're looking for.

I did a quick pseudo-program to see what it would take for a simple test without interrupts, and it was surprisingly easy.

If you can settle on a PIC to use ... preferably 2-CCP's (1 for the FOSC4).
Could probably come up with something that's close.

I love shooting things ... with camera's.