[C_Jones]

Just wanted to portray this scenario:

Pentax K-3II with Cactus V5 trigger, no flash on camera, camera in Manual mode.

Three Pentax AF360FGZ flashes off camera in Manual mode, each of the flashes with V5 triggers, on light stands.

One other flash (4th one), off camera. I will use the Neewer TT560 as a hypothetical example for this flash. In this setup, unlike the other flashes it would not have a V5 trigger on it, but would have its Slave mode set to S1 to react to the single firing of the other 3 flash units.

I am almost certain this is the method that would successfully facilitate the 4th flash that would be reliant on the optical triggering Slave (S1) mode without the use of the radio trigger. I am contemplating a fourth flash, possible choices being the Neewer TT560 or the Yongnuo YN560IV without purchasing more radio triggers quite yet.

My question is whether the above scenario would be effective as far as the 4th flash in S1 mode firing at the same time as the other three flashes.

[Angel Perez]

I have never tried your scenario but have tested the S1 modes on my yongnuo flashes. So in theory that would work assuming your flash able to pick up the other lights. A little easier in a studio setting and from what I hear it can be tricky outdoors because of the sun.

[C_Jones]

That is what I was thinking. Like you said, in a studio it would probably be easier to work as opposed to it possibly being a bit more challenging in the outdoor light/environment.

I guess either the Neewer or Yongnuo would work in their optical slave mode, but most likely if I get another V5 to accommodate one of them I would have sure fire capability indoors or outdoors.

Thank you for your opinion.