Sigma EF-500 DG Super PC-sync port modification
The Sigma EF-500 DG Super is a nice flash for its price (especially since I got mine 40% off when it was discontinued), but unfortunately it does not have a sync terminal. Furthermore, at least the Sony/Minolta version of this flash cannot be triggered in any mode by shorting out the hotshoe contacts (apparently some EF-500 DG Supers can, I don't know if it depends on the system or the production date). This means that a sync terminal cannot be added by using a hotshoe adapter providing this capability (e.g. the cheap FS-1200 clones have the sync port but it just doesn't fire this flash).
In order to use this flash with a radio-frequency wireless trigger (Cactus v4), I decided to add a PC-sync terminal myself. My initial idea was to solder it to the Test-button contacts, but I was given the URL of this post from where I learned that someone had already tried that with little success (apparently it introduced an unacceptable delay).
I decided to try the alternative idea presented on that page: soldering the sync port to the optical sensor (which is used in the optical slave flash mode). I soldered wires to both sides of the optical sensor and indeed managed to trigger the flash by shorting those wires in the “C0 SL” mode, but attempts to use the wireless trigger caused multiple flashes on a single trigger event, which was also unacceptable.
In the end, I discovered that connecting one side of the sync terminal from the optical sensor and the other side from the flash sync contact on the shoe triggered the flash properly. Everything seemed fine and I closed the flash back up to test it, only to find that it went crazy whenever it was in the slave flash mode and the wireless trigger wasn't connected. The problem always disappeared when I connected the wireless trigger, so I decided to “fake” its presence all the time by soldering a 15 nF ceramic capacitor across the sync terminal. This finally solved the issue, and everything works perfectly now.
So, the final version of the modification is:
- PC-sync terminal attached to the foot of the flash
- Pin of the terminal connected to one side of the optical sensor
- Sleeve of the terminal connected to the sync-pin of the shoe (brown wire in mine, but test it and note that there are two brown wires)
- 15 nF ceramic capacitor across the sync terminal pin and sleeve
(The value of the capacitor was an arbitrary choice, there's no real reason for picking that particular value. Also note that it might be more sensible to add a 3.5 mm jack instead of a PC-terminal, but as it happens I had a couple of PC-terminals from a broken camera and no suitable 3.5 mm jacks… If you do put in a 3.5mm jack, read this post about its placement.)
I will not post pictures of the conversion process, partly because I did not take any as I went along experimenting, and partly due to the fact that there are dangerous voltages inside the flash even with batteries removed. Naturally this modification voids any warranty that might still remain, etc, and I don't recommend this to anyone who doesn't feel comfortable doing it based on the brief instructions above (disassembly is easy to figure out, see notes for screw locations and refer to adrian's). I also have no qualifications to know for sure that this modification will not later cause the flashgun to stop working and/or explode and/or turn pink in colour while strobing to the tune of In the Navy. It just seems to work for me, for now. =)
Note that the flash will not fire in slave mode if it thinks that it's on a camera (this is also mentioned in the manual). The included off-camera stand does not cause this to happen, but my cheap FS-1200 clone did. The solution was to drill out a piece of plastic on the top right side of the off-camera shoe (on the Minolta shoe version, I don't know about the others). Use Sigma's off-camera shoe as a reference for the modification.
(I did spend some time testing all features of the flash since I was worried that I might have broken something, but I haven't encountered a single problem in any mode. Actually, as a curious side-effect of the modification, the flash can now be triggered in “C0 SL” mode even by shorting the shoe pins so one does not necessarily even need to add the sync port for use on an off-camera shoe…)