ETTL Flash Power Question

With a 580 and a 430 in ETTL
Let's say I use group A:B with the 580 as A, of course, and set the ratio to 1:2....
Will the 430 fire double the 580 or will it be altered due to the different flash power capabilities? I assume the ETTL will just fire the 430 a little stronger to make it go double whatever it think the 580 should be....


How about in manual if I set the 580 to 1/2 and the 430 to 1/2? I assume the 430 will be less powerful than the 580 at the same setting......

The 580 will put out half the power the 430 emits. A flash can't put out more than its maximum, so the 580 will be gimped accordingly.

In manual, 1/2 is half of what the flash is capable of putting out at 1/1. It's not dependent upon any other flash's capability.

cdifoto wrote in post #13850509
The 580 will put out half the power the 430 emits. A flash can't put out more than its maximum, so the 580 will be gimped accordingly.

In manual, 1/2 is half of what the flash is capable of putting out at 1/1. It's not dependent upon any other flash's capability.

So in ETTL, it is based on the weaker/est flash in the combo rather than what the master is? Does this change if you are using, say, 10 flashes? What if you have 9 580s and 1 430? Sorry, just trying to get a good grasp of the concept.

Manual works as I thought, so thats good.

Thanks for the info!

It doesn't matter which one is master. It depends which one is put in the role of providing the higher output. If the 580 is the master set to 1 and the 430 is the slave set to 2 in a 1:2 configuration, it doesn't matter that the 580 is the one doing the talking. It also doesn't matter how many there are. A 430 can't put out more than it can put out, so it can't be made to put out more than a 580 can put out.

If they each have a separate position, it doesn't matter how many of each flash you have. In E-TTL they're designed to put out a ratio of power...ie a flash will be told to put out an amount of light relative to the other(s).

Now, if you were to put a cluster of flashes together for one purpose --- such as filling a soft box --- I'm not sure how they'd behave in E-TTL (I THINK E-TTL would simply gimp the 430s as a group to produce LESS if needed so that it's equal to double what the 580 can do).

You could, however, get a cluster of weaker flashes in manual to put out more light than one 580 can by itself in the same soft box. I used to line up four Vivitar 283s to hit an umbrella because while each was invidually less powerful than a 580, as a group they were moreso.

Thanks again, CDIfoto!

No problem.

Although I may be wrong about that grouping in E-TTL thing. The system wouldn't have a way of knowing they were grouped together in the same soft box. On that logic it might just fire them independently at the ratio as designated, giving your scenario a ratio of 1: (2 x however many lights you have) so 1:8 if you have four flashes. Maybe.

The cluster thing is all theory to me as I've never tried an E-TTL one.

do the ratios on the camera groups matter if you've got the flashes set to manual? for example i leave my 580 and my 430 at =2/3... and the camera groups at 1:1 then they are both just simply firing at 2/3 their power correcT?

The ratio doesn't apply to manual, since you're independently setting each flash to fire at whatever power you want. The IR system is being used merely to trigger the flash(es).

ok yah thats what i thought. thank you (didn't mean to hijack the thread!)

orena wrote in post #13851069
ok yah thats what i thought. thank you (didn't mean to hijack the thread!)

no worries, i'm done here. use it up!

In a similar vein:

https://photography-on-the.net …/showthread.php​?t=1144295

cdifoto wrote in post #13850905
No problem.

Although I may be wrong about that grouping in E-TTL thing. The system wouldn't have a way of knowing they were grouped together in the same soft box. On that logic it might just fire them independently at the ratio as designated, giving your scenario a ratio of 1: (2 x however many lights you have) so 1:8 if you have four flashes. Maybe.

The cluster thing is all theory to me as I've never tried an E-TTL one.

You were right the first time, Don. In E-TTL mode, the system always considers the ratio of the flash groups and not the individual flash units. So, for a ratio of 1:2, the group A output will always be half as bright as the group B output whether there is one flash in group A and one flash in group B or there are 10 in group A and one in group B, or vise versa--the outputs of each group will always be the same and give you a ratio of 1:2.

PacAce wrote in post #13852263
You were right the first time, Don. In E-TTL mode, the system always considers the ratio of the flash groups and not the individual flash units. So, for a ratio of 1:2, the group A output will always be half as bright as the group B output whether there is one flash in group A and one flash in group B or there are 10 in group A and one in group B, or vise versa--the outputs of each group will always be the same and give you a ratio of 1:2.

Ah. Makes sense. Thanks!

I was doing some testing the other night using my 580EX off-camera and triggering it with my pop-up flash and found some interesting results which led me to the following question:

When using ETTL, is the system able to adjust the flash power below what you can achieve when setting the flashes power to their lowest setting, i.e. 1/128 in manual? A few of my exposures using ETTL seem to suggest that the external 580EX and pop-up flash is achieving a power lower than 1/128.

My tests indicated that ETTL can work to 1/512 power, 2 stops less than what can be set manually.

The effect can be seen with my 580EXII on camera, or on Pixel King radio triggers.