Optical Flash Trigger
 

Here is my new piece of kit, an optical flash trigger that apparently works with all flash guns fitted with a hot shoe. Its no powered and relies on light from a master flash then connects two terminal together triggering the slave flash.

Much as I hate e-bay I did pick it up new or approx £8 including carriage from HK and arrived in a week. The circuit could have been designed an built from items from Maplin but would have cost more than £8!

This now allows me to use my fathers flash (GN 20) dating from the mid eighties.

I'm surprised you haven't been using one of these for ages Stephen, it was one of the very first bits of kit that Don mentioned in this thread. Because of Don's early posts in this thread I bought one (£15 from LCE in Norwich IIRC), and use it to slave my mid 1980s Panasonic flash with its >300V trigger voltage.

To all that have flashguns that cannot be used on modern electronic cameras, these remote triggers are very, very useful. These old guns have negligible value 2nd hand so why not make use of them?

Just out of interest have you noticed if these get triggered on pre-flash or not. I used to have one of these 25 yrs ago. heavens knows where it is now. I think they rely fairly high flash trigger voltage to get their power from. I bought a secondhand flash last year which has a 5 Volt trigger voltage which I currently use with a long PC lead. I'd often wondered if it would work with one of these optical slave triggers.

I'll do some experiments when I get home, and let you know. There's nothing to stop me using the optical slave on my modern flash that only has a 5V trigger voltage. I can slave it from the pop-up on the camera, which also has a P-TTL preflash output if I set the camera to program mode.

I also have 2 of these and unfortunately if you don't want them to fire with the pre flash then you're out of luck, If you look at the Champagne shot thread you'll see the problem I'm having with pre flash.

Rob,

The answers from some testing done tonight.......

I have two flashguns,

1. A National (Panasonic) PE-2057 with a >300V trigger voltage. This is my old film camera flashgun that cannot be used on a modern digital camera without destroying it. It is non-dedicated to a particular camera brand/fit with two "auto" power levels and a full power manual setting. This flash is normally used as a slave, triggered by an optical trigger module similar to that shown by Stephen above.

2. A Sigma EF500 DG ST with a 5V (I think) trigger voltage. This can be safely used on a digital SLR, and also an old film camera - I've just checked this by using it on my K1000, there's backwards compatibility for you. This gun has a fully auto P-TTL mode which utilises a pre-flash pulse for metering, plus two pre-set power levels available for manual flash use.

In addition to these, I have the pop-up module built into my dSLR (Pentax *ist DS). This uses a pre-flash pulse for metering when Program mode, Tv, or Av modes are selected. If full manual mode is set on the camera, there is no pre-flash pulse.

So, the first experiment was to trigger the National flashgun, using the optical slave, activated from the pop-up. As Lello has already said, this does not work if there is a pre-flash pulse; the pre-flash is enough to trigger the module and the remote flashgun does not then synch with the main flash discharge when the shutter is open. When using the camera in fully manual exposure mode, there is no pre-flash pulse and the National flashgun synched perfectly when triggered by the discharge from the pop-up.

The National flashgun was then replaced with the Sigma unit, the Sigma was attached to the optical trigger module and the Sigma set to the low power manual discharge mode. I figured that as the optical trigger had only a single contact on it, there was no point setting the Sigma to P-TTL mode as there would be no communication between trigger module and gun. The Sigma would discharge in synch with the pop-up with the camera set to manual exposure, but only if the pop-up was very close (<300mm) to the optical module.

The same experiment was repeated, using the "Test" button to force a discharge from the National gun, this being used to trigger the Sigma mounted on the optical trigger module. With its higher output (GN28), this was able to trigger the optical module at a reasonable distance and cause the Sigma to discharge.

The results of this testing:
Any pre-flash from the pop-up flash on a camera, or, based on previous experience, a pre-flash from the Sigma in my case, will cause the optical module to trigger the remote slave at the wrong time.

If it is possible to set the camera to not use a pre-flash (try using fully manual exposure mode), then it is possible to get a synchronised flash discharge using an optical trigger module.

If the flashgun on the optical trigger module is an old fashioned model with a high trigger voltage, then it is very easy to get the optical module to trigger the discharge of the remotely mounted gun.

If the flashgun on the optical trigger module is an modern model with a low trigger voltage, then it is necessary to put a lot of energy into the optical module to trigger the discharge of the remotely mounted gun. If you are using the pop-up flash built into your camera, this may not have the required power to trigger the optical module at a realistic distance.

If you have a high powered flash, this can be used to trigger a modern flash mounted onto an optical module at a realistic distance, though this will still be a lot lower distance than can be achieved with a high trigger voltage remote flash.

I've now got spots in front of my eyes from looking at flashguns discharging, so I hope this helps somebody.

Regards,

Duncan

Preflash and remote triggers.
 

After the posts on pre flash and flash triggers I have given some thought to the subject.

I see Duncan has got there before me with a couple of experiments so I will throw mine into the pot. :D

I had a read of my instruction book to ensure that pre flash would be triggered and set the D100 and the D2X up for an experiment. The basis of this experiment was after a flash test, as I was unable to notice the pre flash then its output power is a lot less than the main flash. If this was true then would a black flag as per the attached graphic work. The black flag should in theory shield the remote sensor from the low powered light yet allow triggering by the main flash.

I was unable to prove this, and attach two pics from the test. My slave is so insensitive that no matter what I did I was unable to get it to trigger through pre flash. This does show at least that 1) pre flash is indeed low powered, and 2) there is a sensitivity difference between remote triggers, in that some are blind to the pre flash.

Two pics attatched.

Camera settings on both cameras was Program Mode, 3D Matrix metering and the SB80-DX was set to DTTL.

1) Slave flash OFF. The slave trigger is highlighted in this shot and the Metz 45 in the background is what it is connected to. On camera flash distance to the trigger was 30 inches. So plenty near enough to get preflash trigger when the Metz was turned on. Positioning of the Mez was such that we could see in the image if it fired on time, or was triggered by the pre flash, in which case it would register as OFF. ie fired before the shutter opened.

2) Slave Flash ON . The underexposure here is because the Metz is a far higher powered unit than the SB80-DX that was on the camera. The camera has given correct exposure for the Metz flash reflector. You can see the light from it in the models chimney.

The conclusion from this is, that we need someone with a different remote trigger to try a black flag experiment. Black flag would be a bit of card or such taped to the unit to shied the remote sensor from direct line of sight from camera flash.

Don

SNAP :D :D :D

Thanks for that Duncan. I will have to wait and see if my idea helps out too.

Don

Now you've got me thinking Don. It hurts at the moment....................


I wonder if I use the remote trigger on the Sigma, if the pre-flash off the pop-up will be too weak to trigger it, but the main flash will be enough. I'll have a go tomorrow.

Thanks Don & Duncan - If I get a chance later I'll come back on this one.

I don't think your shielding approach will work Don and I'll explain why.

Found this Thought it looked quite interesting.
http://mysite.verizon.net/jayandriot/Loop.htm

Just to remind folk that my background like Foxy Bob is in electronics. I was an electronics engineer for 25 years and basically lost interest 10 years ago when the majority of equipment became uneconomic to repair. By then most designs were a one chip solution and the manufactures were not going to release any information on its inner workings.

To start with I’d thought I would give you a layman’s guide to the workings of an auto thyristor flashgun. As a word of warning I strongly recommend that you don’t mess with these devices unless you have a healthy respect of high voltages with a large current (250 – 400 Volts DC generated from those tiny AA batteries)

The Bulb is a device called a Xenon tube. It has 3 connections. Applied to 2 of them is the High Voltage (ranging from 250V to 400V dependant on the power rating of the Xenon tube used). This high voltage charge is generated by a voltage converter circuit (the thing you hear whistling) and is stored in a Capacitor.

The camera uses a switch to fire the flash. When the switch operates it sends the trigger Voltage through a step-up transformer to generate high voltage pulse (4KV to 10KV dependant to the Xenon tube used). This high voltage pulse is applied to an exciter electrode on the Xenon tube to ionize the xenon gas inside the tube. The xenon gas suddenly becomes a low resistance and the energy storage capacitor discharges through the tube resulting in a short duration brilliant white light.

Old cameras used a mechanical switch to fire the flash. On flashguns from this era the trigger voltage was tapped off the high voltage supply and was in the order of 100 – 200 Volts. This meant a small step-up transformer could be used to generate the exciter pulse. Flashguns designed for electronic cameras have a much lower trigger voltage (5 – 15 Volts) and use an opto-coupler (electrically isolate) to connect to the former exciter pulse generating circuit.

OK that’s what a cheap and cheerful flash unit does. Then some bright spark came up with away of controlling the duration of the flash with a device called a thyristor. Basically a thyristor is a special kind of electronic switch used to interrupt the current flow through the tube and thereby turn the flash off. On the old auto type flashguns a sensor fitted to the gun provided the turn off signal to the thyristor. On modern TTL metering systems the camera provides the turn off signal when enough exposure has been received.

The above gives us the understanding that the brightness of the flash is not controlled but the duration.

Now we come around to the optical slave trigger device. It is fitted with a sensor sensitive to light. Most appear to use a Cadmium Sulfide photocells (CsS) used in the old cheap and cheerful handheld light meters. There is a whole bunch of theory on light sensors which is important in Gigabit fiber optic links but I won’t bore you with it here. The key thing about this theory is a big sensor has a strong output signal but is less sensitive to very short pulses and the converse is true for a small sensor.
I think the pre-flash is still long enough for the sensor to respond to it well enough to fire the slave.

Now to look at slave flash units that copes with pre-flash. In Saphire’s thread on wedding photography she has such a device. I think Metz also has a unit but it is expensive. These units expect and make use of the pre-flash. In a nutshell the electronics uses the first short flash to generate an enabling signal which is held for a period of say 0.5 second. By which time the main flash has occurred and because its path has been enabled by the pre-flash it goes through to trigger the slave.

Rob,

Burning the midnight oil again I see. :D

Excellent write up on the workings of a flash unit. You are the electronics boffin, so would not disagree with anything you have said.

Your mention of Cadmium Sulfide photocells (CsS) in the trigger is interesting. My trigger of unknown origin dates from the mid 80's so I would not expect the light sensor to be very sensitive. My tests involed every permutation I could think of. Pop up - big flash - distance from trigger, all to no avail

Camera light meter cells went through the route from CDS to SPD with its faster response and greater sensitivity to light, so one might have expected cells used in flash triggers to have gone a similar route. My thought was that if the pre flash is not as bright as the main flash then possibly we could make use of the inverse square law to limit the light intensity the sensor recieves. Hence the black flags.

Graphic attatched.

May work, may not.

Don

Excellent read Lello.

Don

Don

It looks like I may have get my Oscilloscope out of the loft and rig up a sensor circuit to test this out. The Boss has jobs for me at the weekend so it may take awhile.

Another thing to think about while on the subject. If the brightness of the flash was to change then also would its colour. The brightness is very much down to the voltage on the capacitor at the time of discharge. As the batteries age then the Voltage would be a bit lower.

I see on the recent models of Canon flash 430EX & 580EX they attempt to compensate for this by telling the camera what colour temperature to set the camera to.

:D :D :D

Nothing like getting a techie involved.

Interesting thought on colour temp. Must be something in it if Canon recognise a problem. I will have a look when the workshop is freed up, athough I do not have a colour temp meter, so a white card job is the best I will manage.

Don

It does appear you can get digital versions of the optical slave triggers. (peanut) A tad more expensive.

"WEIN products has duplicated the entire line of its popular solid state batteryless slaves in a digital format that can perfectly synchronize with digital preflash cameras."

The Wein PN-XLD for example.

This talks about coping with a 2 preflash system used on Nikon. From what I recall from my past reseach is that Canon has 1 preflash. So I don't know if they will cope with both or only Nikon. Info on this product is a one liner and a bit vague.

i-TTL (or equivalent) optical triggers solved
 

I think the spirit of this thread is to provide studio quality results using bare minimum equipment and lots of brain power.

I have been reading with interest some attempts to use i-TTL or equivalent with optical slave triggers. My initial experiments confirmed that preflash triggers the optical triggers leaving the test shot very much underexposed. A result found above by others.

I thought of a few things to solve the situation by inhibiting preflash from triggering the slaves. I wont bore with the ideas but the final solution was simple kitchen roll used to attenuate light picked up by the optical triggers. I found that a single layer laid across my triggers did the trick. Attenuating enough of preflash not to be effective but allowing main flash to trigger the slaves. Of course a positive result would be a whited out exposure becuase i-TTL could not predict the output of the slaves.

Photos below....

Pic 1 wrapped double layer of kitchen roll, this proved too much attenuation as main flash did not trigger, I knew I was on to a winner.

Pic 2 Jackpot! using a single layer of kitchen roll placed over the optical triggers

Pic 3 as pic 2 but slave flashes switched off.