The autofocus assist requires communication with the camera to work properly. When the correct transmitter matches the camera, additional contacts in the hot shoe receive focus control signals through these contacts to activate and then turn off the laser. Camera and flash transmitter must match for this to work.
You could always resort to my old method of using a Laser Gunsight to put a red dot on the subject for the camera to focus on. It's quite easy to remove the dot in POST using Photoshop or any photo editing software. I had a bracket/handle attached to the tripod thread under the camera, that came up around the left side of the camera, and this modified laser gunsight was attached to the cold shoe that was mounted on the top of this bracket. An included push button on the back of the laser turned it on and off, so completely manual. When going to use it I always explained to the subject what it was and what I was doing, so they didn't think I was pointing a gun at them. Don't scare your subject.
The only modification that the laser needed was a small block of aluminum with grooves on the sides at the top for the laser to attach like it does to a gun, and the bottom portion filed to the shape of a male hot shoe like the bottom of a speedlite, so it would fit into any cold shoe that I chose to mount it to. The little cold shoe accessories with the 1/4-20 threaded hole in the bottom that are readily have a side adjustment to allow tightening the grip to prevent the laser block from sliding out during use, so one of these would be good to use wherever you wanted to add this laser to your rig or cage. If you won't be putting any light or other things on the camera hot shoe, the laser could be attached there as long as the bottom of the block was shaped correctly. I just used hand tools (files) when making mine, but started with a scrap small block of soft aluminum scrap that I found in my shop that was about the ideal size. A little flat black on it when completed made it look like the rest of my camera gear.
I'm not sure where this laser gunsight is, since I haven't used it in over 20 years, but I did find it in the pocket of a camera bag about 5 years ago, so it's still around here someplace. If I can find it, I'll post a photo or two, but it may be a day or so before I can even begin this search.
Charley
