Trigger 2 cameras at the same time...problem

Hi,

I recently bought a RF602 Yongnuo trigger and reciever. I want to trigger both cameras at once to play about with stereo images. But I want to do it in the studio with studio lights...

I tried tonight and had problems, so here's the set-up...can you say what's wrong?

400D - has the Yongnuo trigger on. This is the lead camera, if you like. But with the trigger on the hot shoe, I can't put the lights to the 400D

40D - has the lights in the RF socket. Also has the receiver which has a cable to the trigger socket.

So, theory is, the 400D shutter is depressed, the 400D AND the 40D shutters are activated, the 40 triggers the flash via the RF socket.

Now, all this "worked"...both shutters fired, and the lights fired. but the 40D had a well exposed image, and the 400D had an underexposed image, as if it had "missed" the lights. Now I reckon there must be a delay, with the 400D shutter activating, and closing again before the 40D is triggered along with the lights.
Does the Yongnuo trigger have a delay? Is there any way around this?

I am getting another RF602 receiver soon, so will trigger both the 40D shutter and the lights on the same trigger signal. Would that solve it, do you think? (actually, I will have it so the 400D is the "slave" camera as I am waiting on the relevant cable for that too).

Shutter lag, man. It takes time for the mirror to go up and the shutter to open.

You press the button on the 400D, but it doesn't trigger the other camera until the shutter is actually open (the point at which it would normally fire the flash). So by the time the 40D shutter opens and the flash fires, the shutter has already closed on the 400D.

You won't make this happen if one camera is master and the other is slave. It will only work with two slave cameras, triggered by the same transmitter, and both slave cameras will need to have the same shutter lag (which I suspect is significantly different between the 40D and the 400D).

A possible option, if the ambient light level is very low, is to use a very slow shutter speed on the master camera so its shutter is still open when the slave camera fires.

Curtis N wrote in post #14867270
Shutter lag, man. It takes time for the mirror to go up and the shutter to open.

You press the button on the 400D, but it doesn't trigger the other camera until the shutter is actually open (the point at which it would normally fire the flash). So by the time the 40D shutter opens and the flash fires, the shutter has already closed on the 400D.

You won't make this happen if one camera is master and the other is slave. It will only work with two slave cameras, triggered by the same transmitter, and both slave cameras will need to have the same shutter lag (which I suspect is significantly different between the 40D and the 400D).

A possible option, if the ambient light level is very low, is to use a very slow shutter speed on the master camera so its shutter is still open when the slave camera fires.

Yes, with your response and a couple of others in other fora, I have come to this conclusion. I do have another receiver comeing, so can go for the two slave option. Will try it and see.
The only thing with that is in normal studio work I want to use the 40D as main camera, hand held, and the 400D recording BTS shots. I might not be able to do that if I have to trigger both with a remote to make them sync.

For still life and adults, I can slow the shutters somewhat, but with kiddie shoots that won't work so well - I can't kill all the ambient light, and I can't have too slow speeds for the blur as the kids do cartwheels etc across the floor! ha ha.

Will keep trying.

For the BTS shots, adjust the exposure on the remote camera to get proper exposure from just the modeling lights (or whatever ambient light exists). You'll need to crank up the ISO and suffer some loss of IQ, but I'm guessing those shots won't be printed 24x36 anyway.

Curtis N wrote in post #14867406
For the BTS shots, adjust the exposure on the remote camera to get proper exposure from just the modeling lights (or whatever ambient light exists). You'll need to crank up the ISO and suffer some loss of IQ, but I'm guessing those shots won't be printed 24x36 anyway.

Yes, that is true. Thanks.

Have you tried setting the master camera to second curtain sync and using a slightly slower shutter speed? As the flash won't fire until the shutter on the master camera is about to close, it should give enough time for the shutter on the slave camera to open fully.

Sorarse wrote in post #14867763
Have you tried setting the master camera to second curtain sync and using a slightly slower shutter speed? As the flash won't fire until the shutter on the master camera is about to close, it should give enough time for the shutter on the slave camera to open fully.

No, not tried that. Never looked at 2nd curtain. Will look at it next time though, seems like a plan to start with. Thanks.

Sorarse wrote in post #14867763
Have you tried setting the master camera to second curtain sync and using a slightly slower shutter speed? As the flash won't fire until the shutter on the master camera is about to close, it should give enough time for the shutter on the slave camera to open fully.

That doesn't compute.

If the shutter on the remote camera is triggered when the flash circuit closes on the master camera, and the shutter on the master closes immediately after that happens, then he'll still have the same problem. The master camera won't catch any light from the flash fired by the remote camera.

Your easiest option may actually be dark room flash photography with long shutter speeds. Trip both cameras before manually firing your flashes.

Exactly what kind of subject matter are you attempting to use?

Personally I'm wondering how in sync both cameras would be if their shutters were tripped at the same time (instead of a cascade of one camera tripping the next). I can easily see there being a bit of wiggle room, especially between different models. I haven't come across detailed standards on shutter lag yet.

Luckless wrote in post #14868046
Your easiest option may actually be dark room flash photography with long shutter speeds. Trip both cameras before manually firing your flashes.

Exactly what kind of subject matter are you attempting to use?

Personally I'm wondering how in sync both cameras would be if their shutters were tripped at the same time (instead of a cascade of one camera tripping the next). I can easily see there being a bit of wiggle room, especially between different models. I haven't come across detailed standards on shutter lag yet.

Initially I was just trying to get stereo images, of either static objects or of, for example, myself. Slow shutter would be ok, in the dark, for these options.

I would also like to get some shots with both cameras with some of my customers, though...maybe using the 400D as a Behind-the-Scenes camera, and also to possibly grab shots I can't get with the 40D. In this case, I would need faster shutter, as I would have movement (kids doing cartwheels and the like!), so I'd really like to sort this.

I hope having more than one receiver will help, triggering both cameras rather than one camera triggering another.

More practice needed.

Thanks

Curtis N wrote in post #14867910
That doesn't compute.

If the shutter on the remote camera is triggered when the flash circuit closes on the master camera, and the shutter on the master closes immediately after that happens, then he'll still have the same problem. The master camera won't catch any light from the flash fired by the remote camera.

I was assuming that it was the shutter release that tripped the trigger for the slave camera, but if it's the flash circuit, then you are right, and my solution won't work.

Sorarse wrote in post #14870928
I was assuming that it was the shutter release that tripped the trigger for the slave camera, but if it's the flash circuit, then you are right, and my solution won't work.

Yes, it will be the flash circuit won't it? The trigger is on the hotshoe. It all makes sense now, why it won't work like this. I need 3 recievers, I reckon...one for each camera, and one for the lights. They will all trip at the same time then, eh?

The issue is this...
Pressing shutter of camera 1 opens its shutter immediately...
...but triggers a momentary propagation delay to triggering shutter of camera 2
...which causes the flash to be triggered by camera 2 (a delay from when camera 1 shutter opens)

If both cameras had a suitably long shutter-open time, there would be no issue. But...

You need to press a button (transmitter) which (after the signal propagation delay)
...triggers two radio receivers to trip the shutters of both camera 1 and camera 2 at the same time, whereby
...the flash is triggered by the shutter opening of one of the two cameras

Wilt wrote in post #14871413
You need to press a button (transmitter) which (after the signal propagation delay)
...triggers two radio receivers to trip the shutters of both camera 1 and camera 2 at the same time, whereby
...the flash is triggered by the shutter opening of one of the two cameras

This is what I will be trying when I receive my second receiver...

Thanks

Bend The Light wrote in post #14871273
I need 3 recievers, I reckon...one for each camera, and one for the lights. They will all trip at the same time then, eh?

If you do that the lights will fire before the shutters open.

Shutter lag, man. Shutter lag. When the shutter button is pressed (either manually or via RF system), it takes time for the mirror to go up and the shutter to open. Someone mentioned this earlier in the thread. These are mechanical parts that have to actually move. Your brain will process this better if you watch it in slow-mo:
http://www.youtube.com​/watch?v=6x_YXj0vWVM

But when you close the flash circuit, it fires at... the speed of light. It's all over in one or two milliseconds.

You need both shutters open at the same time, and you need the flash to fire while they're both open.