Photographic slave-triggers

[Lesh]

Thanks for looking.
The red colored hatch is to help the camera focus under dim light conditions.
The preflash(es) on all cameras are so fast that you can not see them. Canon have a system called TTL that communicates with their dedicated flash units. Here is what I am talking about: **broken link removed**
None of this you can see with the naked eye except the main flash.

Edit. The pre-flash is used to set the white balance before the picture is taken.

I would guess that if you can see the 20ms main flash, the 5ms pre flash would be visable. I am taking those numbers from your scope image.

Is anyone familiar with the scan back digital cameras? They have a small ccd sensor which is mechanicly scanned accross the focal plane. Often a small 10,000 pixel sensor, can create a 50 or 60 megapixel image. This is of course at the cost of a 4-5 second exposure time. Of course with such a back, no flash would work anyhow.

 

[crust]

ok, i found a circuit and the pdf is still online. Check out this link: **broken link removed**.

The only difference is that a phototransistor is attached with emitter to common and collector to center pin. I am pretty sure that is it. Hopefully somebody else can chime in and confirm that the pdf is correct. Simple and powered from the flash. I was going to put it together last night, but I did not have any satisfactory SCRs in the bench stock.

Thanks for the scope trace, I had no idea the camera does that. I usually shoot in raw and adjust the white balance on the computer. That is how I did the pictures for the [plug]ps3toothfairy[/plug] device.

 

[Rolf]

I would guess that if you can see the 20ms main flash, the 5ms pre flash would be visable. I am taking those numbers from your scope image.
{snip}
QUOTE]

You would be the first one. I think what is happening is that they are to closely spaced. As an example you can not distinguish the individual frames in a 16mm movie that is projected a 16 frames per second.

 

[Rolf]

Whoa there pardner, I'm not interested in digital cameras for studio work. VERY few have sufficient resolution for SERIOUS photography. A 6X7 colour film, developed properly will allow 6ft X 7ft prints with very little loss of detail. Transparencies do even better. This is real photography, not happy snaps.
Forget the digital cameras in this case, we are back to the original request.
A cheap circuit which will reliably fire a small cheap manual electronic flash. No frills

Now that LASCR's (light activated SCR) are not available anymore, circuits have become a little more complicated. With the LASCR you needed only two components, a LASCR and a resistor. Now you need three components, a 33% increase!

Seriously here is the link to the simplest unit I could find, that meets your requirements, with only three components: **broken link removed**
If you don't have a suitable SCR I'll send you one to save S&H on a small order.

 

[Lesh]

I would guess that if you can see the 20ms main flash, the 5ms pre flash would be visable. I am taking those numbers from your scope image.
{snip}
QUOTE]

You would be the first one. I think what is happening is that they are to closely spaced. As an example you can not distinguish the individual frames in a 16mm movie that is projected a 16 frames per second.

The spacing is 140 ms (1/7 second). I hadn't given thought to the spacing between the flashes. Given the spacing between the flashes, I would guess that you could discern a difference between a signle flash, and the preflash / flash, although it would not appear to be a second flash.

You did say that "The preflash(es) on all cameras are so fast that you can not see them." I disagree, I am sure I could see a 5ms flash.

 

[Rolf]

{snip}
You did say that "The preflash(es) on all cameras are so fast that you can not see them." I disagree, I am sure I could see a 5ms flash.

Of cause you can see a single 5ms flash.
I did not state that very clearly. I meant to say that the eye cant perceive the two flashes as more than one, because they occur to closely.

 

[crust]

Seriously here is the link to the simplest unit I could find, that meets your requirements, with only three components: **broken link removed**
If you don't have a suitable SCR I'll send you one to save S&H on a small order.

I looked at that circuit, and while it might work correctly with some flashes the problem is that many modern flashes have a continuous current between the trigger and the common. If this current stays above the SCR continous on current, then this circuit won't reset. But you could always try it and if it has trouble, add the diode, phototransistor, and try again.

 

[Rolf]

I looked at that circuit, and while it might work correctly with some flashes the problem is that many modern flashes have a continuous current between the trigger and the common. If this current stays above the SCR continous on current, then this circuit won't reset. But you could always try it and if it has trouble, add the diode, phototransistor, and try again.

I know what you are referring to, the Canon EX are an example of flashes that doesn't do well with SCR triggers.
I have successfully used HV transistors to trigger these EX units but then the trigger doesn't reliably trigger all models of the more common Vivitar's.
So it seems like you have a compatibility problem no matter what you do, at least I have not come up with a universal solution.
I don't have a EX to test but I would like to know if a resistor in series with the SCR could help. My three different model Vivitars will trigger when shorted with a 25k resistor.

 

[crust]

I know what you are referring to, the Canon EX are an example of flashes that doesn't do well with SCR triggers.
I have successfully used HV transistors to trigger these EX units but then the trigger doesn't reliably trigger all models of the more common Vivitar's.
So it seems like you have a compatibility problem no matter what you do, at least I have not come up with a universal solution.
I don't have a EX to test but I would like to know if a resistor in series with the SCR could help. My three different model Vivitars will trigger when shorted with a 25k resistor.

I've got an EX, but I don't use it as a slave. I guess I could use the internal flash to trigger it if I build the circuit. The flash I used is some cheap thing that came in two pieces. It had a flash body and then an add-on to make it work with a minolta.

 

[KMoffett]

Here's a homebrew slave trigger that I used for several years. Similar to the one crutschaw posted. The standby current draw was about 0.5µA...I never had to replace the batteries. Because of the choke in the base-emitter circuit it was immune to ambient light levels. I suppose you might replace battery with his(?) resistive-divider/capacitor power supply. I had experimented with a L14F2 photo darlington, with better sensitivity...but never went ahead and changed it.

Ken

 

[Rolf]

The Chinese have done it again ...

I've got an EX, but I don't use it as a slave. I guess I could use the internal flash to trigger it if I build the circuit. The flash I used is some cheap thing that came in two pieces. It had a flash body and then an add-on to make it work with a minolta.

Went to a Dollar store today and picked up two solar powered calculators or so I thought. They had the little tell tale window. I needed the little solar cell for the slave flash trigger I was going to build.
After slaving for several minutes to remove the 6 small screws on the back, I peaked inside looking for the wires going the solar cell, there were none. There were no solar cell either just a piece of plastic and a little battery close by.
Spent some time Goggling but nothing that small was to be found. HELP!

 

[Nigel Goodwin]

Went to a Dollar store today and picked up two solar powered calculators or so I thought. They had the little tell tale window. I needed the little solar cell for the slave flash trigger I was going to build.
After slaving for several minutes to remove the 6 small screws on the back, I peaked inside looking for the wires going the solar cell, there were none. There were no solar cell either just a piece of plastic and a little battery close by.
Spent some time Goggling but nothing that small was to be found. HELP!

It's just a battery power calculator, a common Chinese trick!.

 

[Centretek]

Thanks guys. Problem solved.

 

[crust]

How did you solve it? What were your results?

 

[Centretek]

Used the photo cells from a solar garden light.(found at refuse dump)