DIY slave flash problem

gamgee · 04-03-2008, 05:18 AM

Yesterday, I made DIY slave flash as seen on Carl Vogt webpage.
It uses on camera flash to trigger the slave and it works (triggers) quickly and consistently

BUT, when I tried to test it properly there was NO flash on the photos!

I'll clarify: 1. I press button (can't remember the exact term but it's button alright)
2. Shutter clicks and built in flash fires
3. Slave fires (at least to my eyes) completely instantly
4. On the resulting foto you can see light from the built in flash but no light from the slave (even when camera is pointed straight to the slave flash lamp)

So I tried to lenghten the exposure time to compensate for the lag in the circuit - nothing!
To make sure - slave IS FIRING - my sore eyes are proof of that.
I also tried to change built in flash to different modes (wireles, slow etc) - nothing.
Only time when I managed to capture the flash was when I combined very long exposure time (10 sec) with rear curtain mode for the built in flash. On that (so far unique) occasion, both flashes fired twice - on the beggining and the end of the exposure (slave had enough time to charge because of the 10 sec exposure), and that SECOND flash was captured in the photo.

So, what that gives me?
Is it posible that built in flash fires BEFORE shutter curtain actually opens and then continues to emit light through the exposure but slave flash (old Braun model) has much shorter flash duration and finishes before curtain even starts to open?
So far, that was only reasonable explanation I can think of.

Sorry for the longish post.

**pentagor** · 04-03-2008, 05:22 AM

I think you're right on. It seems to me, that it is a flash sinc problem... don't know how to solve it though.

and · 04-03-2008, 08:23 AM

Whats happening is that your built in flash is p-ttl.
p-ttl meaning that it fires a preflash to measure the light before it fires the actual flash.
So when you press the shutter:
1. on board flash fires preflash
2. slave flash fires
3. shutter curtain opens
4. on board flash fires the real flash
5. shutter curtain closes

thats the problem, thats why a lot of people have 1 set of triggers, for instance 1 pair of pocket wizards, even though they have maybe 4 lights, but as long as you can trigger one light remotely you can use optical slaves on the others.

if your next question is how to disable pttl on the built in flash, its hard. and when it works, what you get instead is a full power burst, so you will have to flag that to prevent it hitting your subject and at the same time hitting the optical sensor of the remote flash.

one way to get the built in flash to fire a full non pttl burst is if you have a lens that has an aperture ring, set the camera to allow for aperture ring and then move the aperture ring to a position other than the A position. the built in flash will not fire a single full power burst that will trigger your slave at the right time.

this is why some optical slaves have delays in them. the nikon sb26 is a good example, it has two slave modes, one of them is called delay and can be used if the triggering flash is pttl or similar.

gamgee · 04-03-2008, 09:05 AM

Thanks guys, that was really helpfull.

**Canada_Rockies** · 04-03-2008, 09:56 AM

Originally posted by gamgee

Yesterday, I made DIY slave flash as seen on Carl Vogt webpage.
It uses on camera flash to trigger the slave and it works (triggers) quickly and consistently

BUT, when I tried to test it properly there was NO flash on the photos!

I'll clarify: 1. I press button (can't remember the exact term but it's button alright)
2. Shutter clicks and built in flash fires
3. Slave fires (at least to my eyes) completely instantly
4. On the resulting foto you can see light from the built in flash but no light from the slave (even when camera is pointed straight to the slave flash lamp)

So I tried to lenghten the exposure time to compensate for the lag in the circuit - nothing!
To make sure - slave IS FIRING - my sore eyes are proof of that.
I also tried to change built in flash to different modes (wireles, slow etc) - nothing.
Only time when I managed to capture the flash was when I combined very long exposure time (10 sec) with rear curtain mode for the built in flash. On that (so far unique) occasion, both flashes fired twice - on the beggining and the end of the exposure (slave had enough time to charge because of the 10 sec exposure), and that SECOND flash was captured in the photo.

So, what that gives me?
Is it posible that built in flash fires BEFORE shutter curtain actually opens and then continues to emit light through the exposure but slave flash (old Braun model) has much shorter flash duration and finishes before curtain even starts to open?
So far, that was only reasonable explanation I can think of.

Sorry for the longish post.

Not quite, but close. The built in flash fires twice. Once is the exposure test flash for P-TTL, the second is the actual flash. You saw this with the 10 second delay. The only way you would be able to use the DIY setup is to get a cheap hot shoe flash and use it instead of the built in.

04-03-2008, 05:18 AM	#1
gamgee Senior Member Join Date: Jan 2008 Location: Osijek, Croatia Posts: 116	DIY slave flash problem Yesterday, I made DIY slave flash as seen on Carl Vogt webpage. It uses on camera flash to trigger the slave and it works (triggers) quickly and consistently BUT, when I tried to test it properly there was NO flash on the photos! I'll clarify: 1. I press button (can't remember the exact term but it's button alright) 2. Shutter clicks and built in flash fires 3. Slave fires (at least to my eyes) completely instantly 4. On the resulting foto you can see light from the built in flash but no light from the slave (even when camera is pointed straight to the slave flash lamp) So I tried to lenghten the exposure time to compensate for the lag in the circuit - nothing! To make sure - slave IS FIRING - my sore eyes are proof of that. I also tried to change built in flash to different modes (wireles, slow etc) - nothing. Only time when I managed to capture the flash was when I combined very long exposure time (10 sec) with rear curtain mode for the built in flash. On that (so far unique) occasion, both flashes fired twice - on the beggining and the end of the exposure (slave had enough time to charge because of the 10 sec exposure), and that SECOND flash was captured in the photo. So, what that gives me? Is it posible that built in flash fires BEFORE shutter curtain actually opens and then continues to emit light through the exposure but slave flash (old Braun model) has much shorter flash duration and finishes before curtain even starts to open? So far, that was only reasonable explanation I can think of. Sorry for the longish post.

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04-03-2008, 05:22 AM	#2
pentagor Site Supporter Join Date: Dec 2007 Location: Ljubljana, Slovenia Posts: 495	I think you're right on. It seems to me, that it is a flash sinc problem... don't know how to solve it though.

04-03-2008, 08:23 AM	#3
and Veteran Member Join Date: Mar 2007 Photos: Gallery Posts: 2,476	Whats happening is that your built in flash is p-ttl. p-ttl meaning that it fires a preflash to measure the light before it fires the actual flash. So when you press the shutter: 1. on board flash fires preflash 2. slave flash fires 3. shutter curtain opens 4. on board flash fires the real flash 5. shutter curtain closes thats the problem, thats why a lot of people have 1 set of triggers, for instance 1 pair of pocket wizards, even though they have maybe 4 lights, but as long as you can trigger one light remotely you can use optical slaves on the others. if your next question is how to disable pttl on the built in flash, its hard. and when it works, what you get instead is a full power burst, so you will have to flag that to prevent it hitting your subject and at the same time hitting the optical sensor of the remote flash. one way to get the built in flash to fire a full non pttl burst is if you have a lens that has an aperture ring, set the camera to allow for aperture ring and then move the aperture ring to a position other than the A position. the built in flash will not fire a single full power burst that will trigger your slave at the right time. this is why some optical slaves have delays in them. the nikon sb26 is a good example, it has two slave modes, one of them is called delay and can be used if the triggering flash is pttl or similar.

04-03-2008, 09:05 AM	#4
gamgee Senior Member Join Date: Jan 2008 Location: Osijek, Croatia Posts: 116 Original Poster	Thanks guys, that was really helpfull.

04-03-2008, 09:56 AM	#5
Canada_Rockies Loyal Site Supporter Join Date: Nov 2007 Location: Sparwood, BC, Canada Photos: Gallery \| Albums Posts: 12,385	Originally posted by gamgee Yesterday, I made DIY slave flash as seen on Carl Vogt webpage. It uses on camera flash to trigger the slave and it works (triggers) quickly and consistently BUT, when I tried to test it properly there was NO flash on the photos! I'll clarify: 1. I press button (can't remember the exact term but it's button alright) 2. Shutter clicks and built in flash fires 3. Slave fires (at least to my eyes) completely instantly 4. On the resulting foto you can see light from the built in flash but no light from the slave (even when camera is pointed straight to the slave flash lamp) So I tried to lenghten the exposure time to compensate for the lag in the circuit - nothing! To make sure - slave IS FIRING - my sore eyes are proof of that. I also tried to change built in flash to different modes (wireles, slow etc) - nothing. Only time when I managed to capture the flash was when I combined very long exposure time (10 sec) with rear curtain mode for the built in flash. On that (so far unique) occasion, both flashes fired twice - on the beggining and the end of the exposure (slave had enough time to charge because of the 10 sec exposure), and that SECOND flash was captured in the photo. So, what that gives me? Is it posible that built in flash fires BEFORE shutter curtain actually opens and then continues to emit light through the exposure but slave flash (old Braun model) has much shorter flash duration and finishes before curtain even starts to open? So far, that was only reasonable explanation I can think of. Sorry for the longish post. Not quite, but close. The built in flash fires twice. Once is the exposure test flash for P-TTL, the second is the actual flash. You saw this with the 10 second delay. The only way you would be able to use the DIY setup is to get a cheap hot shoe flash and use it instead of the built in.