Triggering multiple flash with cord

Discussion in 'Exposure Discussion' started by tkamiya, Dec 27, 2010.

  1. tkamiya

    tkamiya Member

    Messages:
    4,252
    Joined:
    Oct 3, 2009
    Location:
    Central Flor
    Shooter:
    Multi Format
    I'd like to fire more than one flash simultaneously.

    I have two Metz 45CT-3 and I intend to use it in manual mode. My intention is to create a portable lighting kit with umbrellas. For this, I need to fire them simultaneously. I do not want to use a wireless setup or optical slaves but I do want to take one cord from each and fire it together.

    I thought about using optical isolators or reed relays and actuate both from X sync terminal but I know there are adapters that sits in the hot shoe and have aux terminals. The size tells me there can't be much or any electronics in these devices.

    Are these simply connecting flashes in parallel? I measured the trigger voltage on these Metz flashes and they are at 5 Volts or so. So damage by high trigger voltage isn't an issue.

    Has anyone done this?
     
  2. Steve Smith

    Steve Smith Subscriber

    Messages:
    9,083
    Joined:
    May 3, 2006
    Location:
    Ryde, Isle o
    Shooter:
    Medium Format
    I think they are just parallel connections. If the two flashes are the same then you shouldn't have any problems. Even if they don't fire (which I'm sure they will) you will not do any damage to them.


    Steve.
     
  3. Ian C

    Ian C Member

    Messages:
    724
    Joined:
    Feb 8, 2009
    Shooter:
    Large Format
  4. tkamiya

    tkamiya Member

    Messages:
    4,252
    Joined:
    Oct 3, 2009
    Location:
    Central Flor
    Shooter:
    Multi Format
    Oh wow.... I have not seen that. Now I don't have to make one. Thank you.
     
  5. MattKing

    MattKing Subscriber

    Messages:
    16,814
    Joined:
    Apr 24, 2005
    Location:
    Delta, BC, Canada
    Shooter:
    Multi Format
    Trigger voltage concerns?

    Would use of two or three flashes and one of those multi-synch adapters increase the concern with high trigger voltage flashes and newer electronic cameras?

    Would they decrease that concern?

    Would there be no effective difference?

    I certainly don't know the answer, but would like to.
     
  6. photoncatcher

    photoncatcher Member

    Messages:
    173
    Joined:
    Nov 19, 2009
    Location:
    NJ
    Shooter:
    Medium Format
    What about "slave triggers? I have a number of them that I use with multiple flashes. They're reall not to expnsive, and they're pretty fool proof. Then all you need is a decent flash meter. I have one of those adapters pictured, but not sure what "BOX O STUFF" it's in. Since I started using the slave triggers, I've not needed it.
     
  7. tkamiya

    tkamiya Member

    Messages:
    4,252
    Joined:
    Oct 3, 2009
    Location:
    Central Flor
    Shooter:
    Multi Format
    I doubt it, Matt....

    If you connect two voltage sources in parallel, the combined voltage will not exceed the highest voltage source. If there are any difference in two, the lower one will SINK (obsorbe) the higher one resulting in combined voltage in between the two.

    In my particular case, it *should* be safe, especially when each only produces 5 volts or so.
     
  8. Steve Smith

    Steve Smith Subscriber

    Messages:
    9,083
    Joined:
    May 3, 2006
    Location:
    Ryde, Isle o
    Shooter:
    Medium Format
    If you parallel connect two or more different flashes then the sync voltage will eventually rise to that of the highest voltage flash. The sync voltage is usually derived from the flashes main high voltage source via a high value resistor charging a small capacitor. When the flash is fired this capacitor is discharged into a trigger transformer to produce a trigger voltage to the tube.

    If multiple flashes are paralled together then these trigger charges are not independent any more and the same charge will be applied simultaneously to all of the trigger transformers. It is more than likely that all the flashes will fire o.k. but there is a possibility that one transformer could have a significantly lower primary resistance than the others and take more than its fair share of the charge causing the other(s) to misfire.

    Again, I don't think any damage would occur.

    As the only thing which could sink the voltage is the capacitors, they are both going to end up charged to the higher of the two voltages rather than to a mid point.


    Steve.
     
  9. tkamiya

    tkamiya Member

    Messages:
    4,252
    Joined:
    Oct 3, 2009
    Location:
    Central Flor
    Shooter:
    Multi Format
    Steve,

    I was only thinking in terms of internal and equivalent resistance/impedance at the connector and more generically to a circuit with parallel power sources and one load.

    Your explanation of the internal trigger circuit makes sense. When I measured voltage with my old VOM (with relatively low internal resistance), the voltage measured somewhere less than 2 volts. When I did the same with an O-scope with 10x probe (I think it's 10MOhm internal resistance?), it measured 5 volts - indicating that impedance is pretty high.

    Do you have an actual diagram? If a small cap is being charged with high impedance source at the primary side, how would it build up such a high energy enough to generate a flash? Somehow, I'd think the trigger circuit is separate from charging circuit.

    Geez, it's cold here... my fingers don't move smoothly! (and I'm in Florida!)
     
  10. Steve Smith

    Steve Smith Subscriber

    Messages:
    9,083
    Joined:
    May 3, 2006
    Location:
    Ryde, Isle o
    Shooter:
    Medium Format
    Yes. Between 1M and 10M for the source resistance and probably about 10nF for the trigger capacitance.

    Because of this, when measuring the sync voltage with a multi-meter, the voltage measured will be significantly lower than the actual voltage due to the internal resistance of the meter loading the circuit.


    Steve.
     
    Last edited by a moderator: Dec 27, 2010
  11. tkamiya

    tkamiya Member

    Messages:
    4,252
    Joined:
    Oct 3, 2009
    Location:
    Central Flor
    Shooter:
    Multi Format
    There are many internet sources for these flash voltages. I didn't trust them because I have no idea how they were measured. I guess most everybody uses digital VOM nowadays.... I still like (and only have) analog ones here.
     
  12. Ian C

    Ian C Member

    Messages:
    724
    Joined:
    Feb 8, 2009
    Shooter:
    Large Format
    Virtually all trigger voltage concerns relate to very old flash units—most of which have died by now and are no longer in use.

    By 1985 or so most flash units were electrically compatible with the newest cameras. They had to be to be marketable, as flash units that fried camera electronics would be unsalable and be a tremendous legal liability for the maker.
     
  13. bdial

    bdial Subscriber

    Messages:
    5,408
    Joined:
    Jan 2, 2005
    Location:
    NE U.S.
    Shooter:
    Multi Format
    A ganged connector certainly works, and is probably the cheapest solution, but I prefer to trigger the other units with optical slaves which are also cheap (relative to things like pocket wizards) and make positioning the flashes and camera much easier since there is only one camera to flash connection to worry about.
     
  14. Steve Smith

    Steve Smith Subscriber

    Messages:
    9,083
    Joined:
    May 3, 2006
    Location:
    Ryde, Isle o
    Shooter:
    Medium Format
    That's not a reliable method though. The Avo 7 meter I inherited from my grandfather has a low enough internal resistance to trigger any flash which I try to neasure with it.


    Steve.
     
  15. tkamiya

    tkamiya Member

    Messages:
    4,252
    Joined:
    Oct 3, 2009
    Location:
    Central Flor
    Shooter:
    Multi Format
    Yes, I know. That's why I followed up with an oscilloscope with a high-impedance probe. I KNEW near zero reading wasn't real.

    I really don't like digital VOMs. When I use VOM, I'm more less looking for an approximate value and trend. I can read a lot from the speed in which the reading (needle) rises or falls. Besides, most consumer/non-professional digital VOMs are precise, but not accurate. They won't read transient spikes either.
     
  16. benjiboy

    benjiboy Subscriber

    Messages:
    8,533
    Joined:
    Apr 18, 2005
    Location:
    U.K.
    Shooter:
    Multi Format
    I sometimes use 2 Metz hammer head flashes with umbrellas I have one on a stand with a coiled 15ft flash extension lead attached to the camera and the other on another stand with an optical slave trigger attached, I plug the extension lead into my flash meter to take an exposure reading, and then back into the camera. The multiple flash adaptors to fire several flashes to one camera sync socket we used to call Sputniks in the old days can damage the cameras flash sync ability.
     
  17. MattKing

    MattKing Subscriber

    Messages:
    16,814
    Joined:
    Apr 24, 2005
    Location:
    Delta, BC, Canada
    Shooter:
    Multi Format
    Sorry Ian - all of my Metz, Olympus, Bowens and Vivitar flashes are at least 25 years old, and they all work great.