topic Potential TTL issue with speed light and strobe in Speedlite Flashes

Potential TTL issue with speed light and strobe

Jpstones — Sat, 26 Aug 2017 19:55:52 GMT

Hi guys

I'm new to this forum. I hope someone can help with this issue. It's confusing me no end...

I nornslly work with 2 canon 430 speed lights a pair of photic Odin trigger and a console in the hotshoe of my canon 5d3

I just bought an alien bee strobe. The idea was to have a 3 light setup where the speed lights, via the phottix system trigger the alien bee strobe which acts like s slave.

And at first glance it works. The speed lights trigger the strobe.

But bizarrely the camera only seems to see the flash from the speed light. Initially I thought maybe strobe was firing late. So I slowed shutter down but what then happens is the whole image darkens. As if adjusting for the strobe.

Si i thought maybe TTL is the issue. I moved everything to manual. Or tried to. Same issue.

But I think Im missing something in settings in the camera or the phottix console where something is still in auto mode.

Does this make sense?

Re: Potential TTL issue with speed light and strobe

TCampbell — Thu, 31 Aug 2017 16:49:35 GMT

Yep - this isn't uncommon.

The E-TTL systems actually flash TWICE ... but it all happens so fast that you'd swear it only fired once.

1) The camera "meters" the scene with no flash, then...

2) The camera fires the speedlights for a "pre-flash" at a very low power level, WHILE...

3) Metering the scene AGAIN (this time at the pre-flash levels)

4) The camera COMPARES each zone (in the evaluative metering system) against no-flash vs. pre-flash to determine how much of a difference the flash made, then ...

5) Computes how much power should be used for the real flash...and

6) Finally the camera shutter opens and the flash fires at the computed power level.

All this happens so fast, you'd swear it just fired once.

But what happens with third party optical triggers is that they notice the pre-flash and fire in response to that (the camera shutter is still closed) then the camera shutter opens and the E-TTL speedlites fire for the real shot... but by that time the manual flashses have already fired. The camera doesn't get the benefit of the other flashes.

Some optical flash triggers have a swtich that will let you put them in a mode where they fire on the 2nd burst of light... not the first burst of light. This causes them to get tricked into firing when the camera only uses the pre-flash.

The other option is to disable E-TTL and just use all flashses manual (which is probably easier.) If you disable E-TTL mode then there is no pre-flash to worry about.

Re: Potential TTL issue with speed light and strobe

Jpstones — Thu, 31 Aug 2017 18:25:59 GMT

Thanks Tim,

You are spot on. Phottix got back to me and explained this. I got round it by finding a stereo out cable and using it as a sync cable so a fire the Alien Bee that way.

But yes I was stumped. It really looks like it fires once. Thanks so much for your time and response.