Using speed lights to trigger strobes without them firing themselves

[fotographer]

Is it possible to use a speedlight to trigger studio strobes without having the strobe itself fire?

From what I've read you set the speedlight to off but even when I get the word OFF to showup the flashlight still 

seems to fire and to tell the truth I'm not finding the speedlight settings that intuitive.

Im' using an EOS 70D and my lighting equipment is as follows:  (the 2 strobes  are the only things that I want to fire)

1 Digiliter YJB-G300 

1 Bowens Prolite 41A 

1 430EX Canon Speed light

1 550EX Canon Speed light

All suggestions gratefully accepted.

[Skirball]

Without having the strobe fire?  No.  But it can just do the pre-fire, which goes before the shutter opens, so it doesn't affect exposure.  I provided more information in your other thread:

http://forums.usa.canon.com/t5/EOS/EOS-70D-nowhere-to-attach-sync-cable/m-p/125111/highlight/false#M...

[fotographer]

Thanks Skirball - yes I think I've figured it out now, it helped when I realized that the 430EX can only be used as a slave and not as a master 🙂  Thank you for your help!

[RobertTheFat]

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@Skirball wrote:

Without having the strobe fire?  No.  But it can just do the pre-fire, which goes before the shutter opens, so it doesn't affect exposure.  ...

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At the risk of sticking my snout into a subject (use of multiple flashes) about which I know nothing ...

So the target strobe sees the pre-flash. How does it know how long to wait before firing? If it fires immediately, the shutter won't be open yet, right? Is the pre-flash always a predictable duration ahead of the shutter? Or is it just assumed that the first curtain will be out of the way before the strobe can react?

Presumably the question doesn't occur with a radio trigger, since the radio signal can be sent after the shutter is fully open.

[Skirball]

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@RobertTheFat wrote:

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@Skirball wrote:

Without having the strobe fire?  No.  But it can just do the pre-fire, which goes before the shutter opens, so it doesn't affect exposure.  ...

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At the risk of sticking my snout into a subject (use of multiple flashes) about which I know nothing ...

So the target strobe sees the pre-flash. How does it know how long to wait before firing? If it fires immediately, the shutter won't be open yet, right? Is the pre-flash always a predictable duration ahead of the shutter? Or is it just assumed that the first curtain will be out of the way before the strobe can react?

Presumably the question doesn't occur with a radio trigger, since the radio signal can be sent after the shutter is fully open.

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Easiest question first: Correct, with radio triggers there isn't a pre-flash.

As to TTL optical triggers: Yes, there is a set duration between the preflash and final flash. I don’t know how long that is, but I’m sure Canon has an internal spec for it. Third party flashes that work with the Canon system probably just reversed engineered the delay. The speed at which the electronics work (microseconds) and low powered flash durations (around 1/10,000s) is several orders of magnitude faster than even the fastest shutter speed (most cameras can’t sync faster than 1/250). So it gives you a decent amount of wiggle room.

But it’s not uncommon when working with a lot of flashes to occasionally get shutter shadow when right up against your max sync speed. Although the shutter speed at max sync is much slower than low powered flash, that margin gets smaller when you consider that the flash needs to start after the first shutter completely falls, and the second starts. If you happen to have a flash at max power the duration is actually on about the same order as a shutter duration, and all of a sudden you don’t have so much wiggle room.

Note that not all third party flashes work with the Canon preflash system. Most of the dummy optical triggers simply ignore the first flash and then fire as soon as they sense a second. This system won’t work with the Canon system if it’s set to preflash only.