Back towards the beginning:
The circuit is a 3.6V Lithium battery in series with a switch. This output is connected to 30 cameras in series..
The camera firmware recognizes a signal of 3V as a shutter release. Thus, when the switch is pressed, the circuit completes and a shutter release signal is registered..
Now I don't know if this is true of most cameras, all cameras or a case by case camera basis but I can speak for a few. I have both a Canon EOS 10D and a Canon EOS 7D. They each use the same configuration for remote focus (in the auto focus mode) and remote shutter release. Their configuration
can be found here. If I read from either the auto focus pin or the shutter release pin to ground I see about 3.3 volts present. Placing either of those two pins to ground performs their assigned action. Essentially placing either pin to a logic low triggers it. There is no need for an external voltage. The camera provides everything.
Based on my own cameras to remote trigger the shutters it would be a matter of using a switch type device to place the designated pin to a logic low (ground). I would think an NPN type transistor could do this, along the lines of a 2N3904 or 2N2222. That is a guess but I doubt any current to speak of is involved in this. The 3.3 volts provided by the camera is likely through a pull up resistor since it gets placed at ground.
I also do not know as I have not experimented with it how long the designated pin must be held at logic low for it to work. That would be another consideration.
As to the use of the good old 4017 Decade Counter / Divider. The 4017 will sequentially make 1 of 10 outputs go high for each incoming clock pulse. Those outputs could in turn likely drive transistors as I mentioned earlier. The 4017 can be setup to count to N and halt or count to N and recycle. The chip does offer a CO (Carry Out) pin to allow cascading.
If I wanted to sequentially fire the shutter release of ten cameras configured as in my link, this would be easy to do. Cascading two 4017s would seem a good way to increase the outputs from 0 to 9 to 0 to 99 but there is a problem I think. The first chip would count 0 to 9 and the CO would increment the second chip up one count. Then the first chip would repeat the count and increment the second chip up another count. At that point the first 10 cameras would want to or be triggered to shutter release again.
I am sure this could be done using a PIC but will leave that for those like BlueRoom who live and breath PIC chips.
I would likely create a disaster using them for this application.
Ron