16. Jul, 2017

Adding fiber optics to electric sync

Is it possible to implement a LED trigger in DSLR/housing combo that is primarily designed for electrical  triggering,  with no facilities to trigger the strobes optically?  As often repeated in UW articles, LED triggers do not drain the battery and have less heat build-up than an internal flash.  The camera does not not have to wait for the pop up flash to recycle, meaning faster shooting, that  is as fast as your external strobes can handle or you buffer can take  (see also my earlier strobe review in the Technical section).

Ikelite SLR: advantages of adding fiber optics For many years I have been using the Ikelite SLR housings designed for the Nikon DX series (D90, D7000, D7100 and D7200, respectively). The Ikelite-style bulkhead and plugs are widely recognized as the most reliable waterproof strobe sync connections available with superior TTL functioning. Still, the hazards of electrical connections interacting with seawater can never be completely ruled out. According to Murphy’s law  ‘anything that can go wrong  (corrosion, broken cables or connector pins, leakage)  will (one day) go wrong’.  Most tricky are small hidden defects like a worn out O ring or a slightly corroded contact that for years will  not cause any problems, but one day will definitely show up and cause a malfunctioning of your entire system. Which leaves shooting with ambient light as the only alternative for the rest of your diving trip. With optical systems there  are no sync cables to flood or corrode or  connector pins that can break. With a LED trigger  in the Ikelite housing I would have the optical system as a back up, in case of malfunctioning of the electrical circuit.

Finding a small LED trigger Although optical triggers are becoming more and more compact,  they  still  need a specially designed housing with enough space above the hotshoe. Limited  space  above the hotshoe of my Ikelite SLR housing (less than 20 mm) not only prevents Nikons internal flash to pop up,  but even to mount any of the available LED triggers.  One option is the mini LED trigger designed by  Hedwig Dieraert some years ago. The trigger is placed on the camera's hotshoe, but instead of inserting the LEDS directly in the trigger contacts, I used a cable connecting  the contacts with a separate LED adapter. This adapter containing two LEDS was attached with some double sided adhesive tape on an empty spot  on the lower frontal dry side of the  housing, facing directly the cable insertion port on the wet side  to plug in the fiber optic cables (see picture above). An easy way to attach fiber optic ports to  any  transparent housing is to use a fiber optic mounting block  or universal mounting kit which can be purchased from UW dealers. This ensures that the LEDS are always aligned correctly with the optical cables inserted at the outside of the housing.*  

Finding the right cable The following step was to find a way to fire the substrobes. To make the DS 161 strobes respond to LEDs  you have to plug in Ikelite’s 4401.1 optic adapter. Unfortunately, the strobes did not fire even when I used a multicore cable. Probably because the LED signal is attenuated when passing through Ikelites transparent housing. Inspired by a DIY photographer suffering from the same frustration, I ordered some end-glow cable of 4 mm diameter which sells for about 5 Euro per meter. After attaching two pieces of cables (cut to 70 cm length) to the fiber optics ports, the strobes appeared to fire flawlessly.  A small piece of electrical tape, or -even better- 4x7mm flexible pvc tube shifted over  the cable endings suffices to make a firm connection between the cable end and the port entries (picture above). To avoid the cable to cross the field of view  of my fish eye lense plus mini dome, I lead them upwards with a piece of tape. Obviously the location of the mounting block (see  picture) prohibits to use the cables with larger diameter domes.*

Another solution would be to mount an optical bulkhead directly on the outside (wet) side of the Ikelite housing by screwing it in a port of an unused control button (like the Fn or BKT button). This would avoid the problem of transmitting (and attenuating)  the LED signal through the tranparent housing as described above. And it would probably also permit to use standard multicore cables, instead of the wider cables. I am still exploring this possibility.

To conclude, it seems that the problem I mentioned in the first lines of this blog has now finally been solved. With larger diameter optical cables the LED signal that passes the transparent housing is still strong enough to fire the strobes. I now have the optical system to back up the electrical system in case of failure (and vice versa). If 'anything goes wrong' with firing the DS strobes it is unlikely that it will spoil my diving holiday. 

*Final notes:  

1.UW Technics has recently released an external optical converter that might just be Columbus' egg. Here, both trigger and LED are combined in a small optical bulkhead. The bulkhead has to be placed on the outside of the housing via a M14 port, and  connects inside the housing  via  a small cable and hot shoe connector with the cameras hotshoe. The same firm also produces  optical TTL and wire TTL ouput with the same trigger device, another  really  nice  innovation in UW light control.

2. A smaller diameter end-glow cable of 2.5 mm diameter later seemed to be a better choice. This cable allows to insert two cables directly into a single Rubber Bush two hole adapter, allowing to fire two strobes.