Electronic Cameras vs Trigger Voltage
— Or —
How Not to Fry Your New Camera

By
N. David King

As internal electronics have taken over the running and functioning of cameras, an interesting vulnerability has surfaced when using after-market or other electronic flash units that are not matched for your camera, such as studio strobes and professional portable flash units.
Strobes fire when a circuit carrying a voltage potential generated by the flash unit’s capacitor and traveling through the PC/Synch cord is closed in the camera. This is called the flash unit’s “trigger voltage.” In the days of mechanical cameras, there was nothing susceptible to high voltage — with the possible exception of the photographer who managed to ground himself through the camera at an inopportune moment.  
As the electronic age found its way into camera manufacturing and then camera functions themselves, and greater and greater computing power was required for more and more functionality.  Just as is the case with computers, faster more sensitive components are increasingly less tolerant of voltage spikes beyond a specified amount. 
This is especially applicable to the newer digital cameras from point and shoot, SLR-Type, and SLR models.  These cameras are basically little graphics computers with a lens hanging on the front.  The faster and more powerful they become, as evidenced by more and more computer-driven functionality and internal processing of the captured image, the more vulnerable to electrical spiking they are. 
The problem is that some flash units and even some infrared remote triggers —especially older ones — use higher voltages in the trigger circuit than the newer cameras are designed to carry.   The amount of voltage is a function of the strobe’s capacitor and not of the size battery you are using.  Just because it uses AA batteries does not mean it might not smoke your new camera’s sensitive computer.  
More and more, camera manuals are making it clear that using flash units not specifically noted and approved might damage the camera and void any warranty.  Without further explanation, this sounds simply like a ploy to get you to buy their brand of flash.  But there is actually a reason for it: flash units other than those they have tested and approved (and face it, they are not likely to approve another brand’s equipment when they are trying to sell their own) may have more voltage than the camera circuits can handle. This is especially true of Canon cameras.  Canon US has made it clear, for example, that the “Powershot G” doesn't like voltages over 6 volts and they’d be happier if that was all you put through any of their cameras.
Nikon has specified 12 volts for their speedlight circuits... though some sources say the Coolpix cameras should take no more than 5 volts.  Of course some Nikon reps claim that Nikons can handle all the way to 250 volts.  I’d rather they proved that with their own cameras however; especially since all of Nikon’s approved speedlights put out 6 volts or less.  Just coincidence?  I’m sure... 
Olympus too recommends strobe triggering in the 3V to 6V range.
Fuji insists their cameras have a 400V center pin limit which is a LOT of voltage but some electronic flash power packs have that much voltage in their trigger circuits.
Confusion abounds because there actually is an ISO standard in place for trigger voltage.  But it is a voluntary standard that seems to be ignored pretty much across the board.  And older strobes are truly unknowns since some can put out trigger voltages as high as 600 volts!  The bottom line however is that if you have a newer breed of electronically operated camera, especially a digital one, use of a strobe with a trigger voltage of over 12 volts is done at your camera’s peril and over 6 volts may be pretty shaky for all but some Fuji and Nikon bodies.  Canon has claimed for the past few years that now their bodies, as Nikon advertises, can handle 250 volts.  But, just like Nikon, ALL of the strobes they recommend as safe for their cameras have less than 12 volts!!!  I’d be happy to test it with your camera but not with mine. 
That is important because most school equipment in the form of the Norman or Speedotron Power Packs, put out considerably more than 6 volts.   In fact the 2000 WS Powerpack is rated at 48 volts.  Profoto units put out 22-25 volts, Speedotrons put out 60 to 70 volts (though they sell an optional power adapter).  Balcar units can put out over 200 volts and Calumet/Bowens units have been measured at 30 to 170 volts of trigger voltage.
In addition to the voltage per se, most electronic units as well as the camera circuits are DC based and can be instantly damaged by reversed polarity.  Older power packs with so-called “household” style jacks for the synch cords are frequently worn to the point where the prongs will go in EITHER way.  With older cameras, all that happened was the strobe may not fire.  With newer ones you may instantly fail the smoke test with your new image catcher.
The problem isn’t limited to studio level strobe units either.  Even your portable flash needs to be checked for trigger voltage.  Two of the most popular flash units over the years have been the Vivitar 283 and its cousin the 285.  Some older 283s (pre-87 models) have been measured at over 600 volts!  Modern ones are supposed to run around 12 volts  But reports of over 260 volts when powered by a Quantum battery have been reported.  
Vivitar 285s seem a little better regulated with newer units running in the 12 volts range.  But look closely at the model number.  Vivitar claims that the 285 HV model is 12 volts while the plane vanilla 285 has a voltage of 350 volts!  Moral: make sure which one you have!  Then test it!
So, OK, I’ve managed to scare you sufficiently… what’s a poor photographer  or photo student to do?
Well, first you should see if your electronic flash unit or units are listed online, along with its trigger voltage, at the following URL:

 	 www.botzilla.com/photo/strobeVolts.html.  
If your flash is listed and has a safe voltage based on your camera’s specs, then there is no problem.  Use it in continued good camera health. 
If it is not listed — or if it is listed and a wide range of variables is noted — then you can easily test your personal strobe yourself if you have a good multimeter with an impedance of 10 mega-ohms or higher.  Turn on your strobe unit and let it power up ready to fire.  Measure the voltage across the two electrodes.  Usually the center pin is the positive and the pin designed to contact the hot-shoe rail is the negative.  Depending on the unit, you may have to then manually fire the flash to get the reading.
If your flash units are putting out voltages that are too high for your cameras, then you need to take some protective steps.   The easiest of course would be to retire the flash unit or relegate it for use with older mechanical cameras for which it was designed.
If that is not a workable choice for you, or, such as is the case where you have to use school or rental units, there are three common solutions.  
The first and easiest is to purchase (for $50 to $60 dollars) a power regulated hot-shoe adapter such as the Wein “Safe Synch”™ adapter which will handle incoming voltages up to 400 volts and yet output only 6 volts which is safe for nearly any camera. This slides into the hot shoe in place of a strobe.  A PC cord can then be attached or a portable flash unit can be plugged in directly to the hot show on top of the adapter.
If you take this route you may discover that with some new but small cameras (such as some of the pro-sumer SLR Type digital cameras) that have a built in flash unit, those units need to be able to fully open the flash head for the camera to function even with an external flash.  The regulated adapters are larger than normal hot-shoe adapters and may interfere with the opening of the flash head.  Sometimes the center contact is large enough that you can purposefully not fully seat the adapter and it will still work while allowing the flash to open.  My old Nikon d5700 and d9700 were like this.
A second approach is to use your camera’s built-in flash to trigger a photo-cell (slave) trigger attached to the strobe unit itself.  This is a common way to fire multiple strobes, and in fact is the normal way multiple monolights trigger each other.  Such photo cells are built into some of the newer power packs to allow the firing of multiple power packs when you need more lighting instruments than can be plugged into a single pack.
Most individual slave units you can buy have a large photocell and are easy to trigger.  However some of the photo cells built into powerpacks or monolights are small and need a clear, unobstructed line-of-site view to your camera’s flash.  And they need to see a fairly bright flash to fire since they are designed to be operated in ambient light.
I recently tested this approach using Norman 2400WS packs which are commonly used in schools since they are like tanks and nearly indestructible.  If the pack were sitting flat and any shadow of an umbilical crossed the photocell, it would not fire predictably.  However, by sitting the case against a sandbag at an angle so the photo cell was aimed more directly at the camera’s flash unit, it fired every time so long as I was within 6-8 feet.  The further I got from it the more sporadic was its response to the camera’s little flash unit.
But, unlike normal slave units that seem to fire nearly simultaneously with the main unit, this one had a delayed reaction, sort of like firing a flintlock rifle.  I do not know if that was a result specific to the photocell in the power pack or was because of the dim flash unit on the camera making the power pack’s photo cell wonder if it was supposed to fire or not… 
(Before you ask, the on-camera flash was so anemic compared to the main lights it had no effect on exposure except that it put another catch light in a model’s eyes. )
Some Canons however perform a pre-flash for auto-exposure and some cameras fire a pre-flash for automatic red-eye reduction.  These will unfortunately fire the main strobes on the pre-flash so those models are not workable with this approach. So a third and very workable option is to use a radio trigger.  
It’s your call how you deal with this potential problem… or not.  Personally, a safe synch unit seemed far cheaper to me than replacing a whole camera because of a fried circuit board.  I also commonly use a radio trigger since it also means one less cord to fall over…