Hi Jim,
Thanks for the info. I read a review today of my Sony a6500 by Jim Decker at Backscatter about the use of optical flash. Apparently the camera does not have the capability of reducing flash power to cut the popup flash recycling time. Using electrical connections changes things as you point out. One surprsie was to see I can shoot with a higher sync speed than the paultry 1/160 sec that the popup flash uses. Apparently the electrical connection allows a 1/250 sync speed which is very advantagous for that black background look. I've never been real happy with the slow flash sync speed of the Sony's compared to 1/250 for my old Canon rig.
I'm going to take your advise and keep the dual flash cord since I shoot with dual Inon Z-240's that have electric inputs. My Inon S-2000 I use for back and side lighting, and sometimes for a lighter travel rig, has a small mirror for flash trigger of the main. My optical cables and popup flash can always be used for backup in case there's an electrical issue.
I'll contact Reef and see what connector I need for the housing and camera to switch over to electrical trigger. If you have any such connectors, let me know and I'll purchase from you.
Happy diving,
Marshall