Hacking the Sigma EF-500 DG Super strobe : Sync port – part 1

Recently I’ve been starting to learn more about flash photography compliments of The Strobist.
Then I bought a set of cheap ebay wireless flash triggers to alow me to trigger the flash remotely, but with the Sigma EF-500 DG Super flash, that was not possible.

UPDATE: Recently purchased a set set of Yongnuo RF- 602 2.4 Ghz wireless triggers from ebay (they’re quite cheap), and they work flawlessly with the Sigma flash, without any modifications. If you want a sync port, try the method below, but if all you want is to trigger the Sigma flash, buying a set of the RF-602 triggers is by far the simplest way of doing it.

Most other flashes out there can easily be triggered by shorting out the two main terminals on the hot-show. But not on this sigma. So I had to find another way to trigger the flash manually, which led to the decision to hack my flash to get a sync port.

What follows is my own documentation of what I did to my unit.I will not be responsible if you accidentally destroy your flash, or worse, hurt yourself: capacitors in the flash can hold their charge for a long time waiting for someone to poke them the wrong way.
WARNING: This hack will FOR SURE void your warranty. This hack also involves permanently modifying your unit. This hack involves a little soldering.

My setup equipment for testing is a Canon Digital Rebel XT, the Sigma EF-500DG Super and a set of the cheap ebay wireless triggers. I have modified a receiving unit to add a 3.5mm sync port to it, so I could trigger an eventually modified Sigma strobe.

The first thing I did was to research what others had done. Found nothing more then a few ideas, one of which was to use the Test button as the triggering point.

So after taking the flash apart, and tracing the contacts used for the test button, I came up with the following 2 points on the main board of the flash.
Be careful when taking the flash apart. The small board that is attached to the battery compartment holds the capacitors that store the high voltage. Be careful not to short anything out.

Testing the flash unit with this setup yielded dissapointing results.
Any shutter speed faster then 1/20 of a second produced black images. That means that there is a delay between the button push and the strobe light of just under 1/20 of a sec.

For me, this is not acceptable.

So after going to bed that night (and sleeping on the problem) I had an idea in the morning.
Why don’t I piggyback on the optical sensor that the camera uses in optical slave mode? So I soldered the sync port wires to the back of the optical sensor.

At this point, things got messed up.
I don’t rememberer if I got any successful triggers from the camera, but the flash started to behave unexpectedly. When set to Optical Slave mode, it would start discharging on it’s own repeatedly, none of the buttons would function… not even the on/off button. Opening the battery door would reset everything. Let me re-iterate that this behavior only occurred in the Optical Slave mode. All other modes worked just fine.
After some frustration, I decided to physically disconnect the sensor itself from the circuit board. Once that was done, the erratic behavior disappeared. I guess I somehow must have messed up the optical sensor? I will have to do some testing on it to try to understand what happened.
I don’t know if you’ll encounter the same problem with the optical sensor. This is just what happened to me.

There is one other weird issue with this mod which I should mention. For every shot triggered by the ebay wireless trigger, I get 2 flashes one after the other. I don’t yet know if this due to how the trigger sends it’s signal… need to investigate further.
But it doesn’t really concern me too much.

Sync speeds up to 1/200 work beautifully. The sync port works as one would expect, but only when the flash is set to Optical Slave mode. And obviously lost the ability to trigger the flash in optically, but I’m not terribly worried.

I am actually quite happy that I can now trigger this flash remotely, despite all the imperfections in its functionality (which to me at best are small annoyances)

UPDATE: (31 Oct 2008)

I’ve been playing with the flash for a couple of days now, and the flash still goes crazy when I put it in optical slave mode WITHOUT having anything attached to the sync port (screen goes wild with random lines, flash charging and discharging itself).

All other flash modes work without any problems. Just the C0 SL mode (oprical slave).

Once I attach the ebay flash trigger (in my case it’s the only thing I have with a sync port) that behavior dissapears. If the flash goes wonky, I have to open the battery door, and close it, in order to reset everything. Then I attach the wireless trigger to the flash sync port, and turn the flash back on.

UPDATE: 20 December 2009
Did some more testing, since I wasn’t happy with how the C0 SL mode was working. I’ve pulled the optical sensor from the flash, for a test. It appears that the resistance of the optical sensor increases with light.  The starting resistance is about 1MΩ. I will have to stick it on a scope to find out how much the resistance will change when a flash is fired, so I can try to emulate that in electronics.

Part 2 will show you how to get the sync port put on the flash body.

21 thoughts on “Hacking the Sigma EF-500 DG Super strobe : Sync port – part 1

  1. K

    Why you didn’t connect wires to hot shoe contacts? It would work (as far as I remember my Sigma) in any mode and without disconnecting anything.

    Camera (and any other flash trigger) is basically a momentary switch. With newer cameras (mechanical contact switched for electronics) you just have to be sure to have correct polarity.

    EOS cameras for example are triggering flash by changing polarity, when flash has switched + with – it will trigger when connected and hang up flash and/or camera.

  2. adrian

    On this Sigma flash, connecting the two main hot-shoe terminals does not trigger the flash. I wish it was that easy.
    I should have mentioned in the original post that this was a problem. Will add this bit of info.

  3. Filip S - Lilit.dk

    I have used the EF500DG super with my wireless trigger cactus PT04.
    I am using the hot shoe but I found that I need to change mode to SLave and manual mode also, while the canon 550ex I just need to connect to the hotshoe and it works – so it first I did not think the trigger was working with the EF500DG super ETTL2 but it does.

    My display look like this http://lilit.dk/foto/index.php?id=4023

    Anyway great hack, maybe an external power supply would be
    a nice feature to hack.

  4. adrian

    You are correct Filip, however, have you tried putting the flash in anything other then full power?
    At full power, you get one flash, but as you decrease the power (1/2, 1/4, 1/8…) you get many more light bursts per trigger. It appears that the flash will pop a flash (at the intended power setting) as long as there is a contact made by the triggering device.

    Which is why I decided to go after the optical mechanism. It only flashes the bulb twice, on anything other then full power (where only one burst of light is produced)

  5. Pixonian

    I’m thinking that there could be various modifications of Sigma 500DG Super flash — those that allow triggering through main terminals and those that don’t. I happened to have a Sigma flash that allows triggering through main terminals, but I still need to set the flash to C0 mode. This will cause the flash to get triggered by other flashes in the room as well. To get around that problem, I had a black plastic card attached to the optical sensor so that flash gets triggered only by the radio signal. What I wanted to do is to be able to tigger the flash without the need to switch to C0 mode — user experience is horrible for that. Didn’t spend time investigating how else the flash can be tirggered, it might be possible.

    See modifications here:

  6. michael przewrocki

    maybe this is what you need:
    pocket-wizard or a tool
    multiblitz germany offers.
    btw: for my analogue cameras i could not use a yashica af-flash eighter, except the corresponding yashic af-cameras.

  7. Pingback: Hacking the Sigma EF-500 DG Super strobe : Sync port - part 2 | adrian’s blog

  8. Pingback: Hacking the Sigma EF-500 DG Super strobe : Extra head rotation | adrian’s blog

  9. Chris H.

    Hi! The pictures that accompany this tutorial are gone. I’m trying to do this modification myself and would love to see what you did. Thanks!

  10. Kimmo Kulovesi


    Thanks for posting this; I had the same idea of soldering to the Test-button contacts but this page me saved the trouble of trying that. I ended up doing a similar optical sensor modification as you, but I got better results when I only connected one side from the optical sensor and the other side from the hot shoe sync terminal.

    Still, I got the same experience as you with the flash set to C0 SL mode – went crazy on its own when used in that mode without anything on the sync port. Since connecting a radio trigger to the sync port solved the problem, I soldered a small ceramic capacitor (15 nF) across the sync terminal. This solved the problem – everything works properly with or without something on the sync terminal.

  11. adrian

    Does the optical slave part work for you as well (with the capacitor in place)?
    Can your flash still be triggered optically?

  12. Kimmo Kulovesi

    adrian: Yes, with the capacitor in place everything works as usual, including optical triggering. I spent some time testing this, since I was worried about breaking the standard functionality, but I didn’t encounter a single problem in any mode after installing the capacitor.

    The downside of having the optical trigger operational is that there’s no mode to trigger the flash _only_ via the sync port (other than covering up the sensor), so it will be sensitive to other flashes going off in the vicinity even with an RF trigger attached. There might just be sufficient room left inside the flash to put in a toggle for the optical trigger, but I think I’ll leave it as it is for now. =)

  13. Barron Chung

    Do you know what, I’ve got this flash, and you can use the standard hotshoe mount if you put it into slave mode, but instead of “C0 SL”, you use “C1 SL” or “C2 SL”. I think FlashZebra had instructions on his website about this, I couldn’t get it to work either until I changed it to this mode.

  14. adrian

    What you will find is that (while in C1SL or C2SL mode) when you choose something other then full power for the flash (ie, 1/2, 1/4, 1/32 power) the flash will act as a strobe, firing off multiple bursts of light at the lower setting.
    Not very convenient if you want to use anything other then full power.

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