ST-E2/420EX/580EXII/5DII body - compensation

Hi

It seems I can use the ST-E2 to adjust the relative exposure between the strobes up to 2 stops, but also set the 580EXII to up to 3 stops compensation on the flash itself, and also set overall flash compensation on the 5DII up to 2 stops.

Are these settings supposed to be cumulative or does one affect the other, eg:

If I set the 580EXII to +3 stops on the flash, and the body to +2 stops, should I expect the exposure from the 580EXII to be 5 stops more exposed?

John

They're not cumulative. Usually one system will override another. When I put my 580EXII on hot shoe and set the flash compensation, it'll override the one set on camera.

If you set FEC on both the flash and the body, the flash setting over rides. They do not add together.

I have to type faster.

Is this true even with the ST-E2 involved (flash not mounted on the body and thus not 'fully' communicating with it - only via the ST-E2)?

wibbly wrote in post #11781912
Is this true even with the ST-E2 involved (flash not mounted on the body and thus not 'fully' communicating with it - only via the ST-E2)?

... so with the ST-E2 and the two flashes, if I set:

-> ST-E2 to 1 stop in favor of the 580EXII (ratio 1:2)
-> 580EXII to +2 stops comp on the flash
-> Overall flash comp on the body to +2 stops

What is then the contribution from each flash to the final exposure?

wibbly wrote in post #11781935
... so with the ST-E2 and the two flashes, if I set:

-> ST-E2 to 1 stop in favor of the 580EXII (ratio 1:2)
-> 580EXII to +2 stops comp on the flash
-> Overall flash comp on the body to +2 stops

What is then the contribution from each flash to the final exposure?

The total FEC of the flash in the example given above is +5.

Leo, are you sure? I do not think they will add like that unless I am not understanding the example.

I have never used the ST-E2 but I would think that since the two 580's have to be in slave mode to talk to the ST-E2 that the FEC you set on them would be ignored or reset by the info transmitted to them by the ST-E2. It would be the FEC set on the ST-E2 that would take precedence over anything set on the camera body.

Here is a quote from the 580ex manual-

Any flash exposure compensation amount, high-speed sync (FP flash), FE lock, FEB
amount, manual flash, and stroboscopic flash settings set with the master unit will all
be automatically transmitted to the slave units.
So my understanding of the above example would that the +1 set in the ST-E2 would be transmitted to the remote 580's and the +2 in the body would be ignored. The +2 set in the flashes would be reset to the +1 that the ST-E2 sent to them. I could be wrong since I do not have the equipment to test it.

Edit:When looking at the manual for the ST-E2 it states that FEC has to be manually set on the slave flashes. It does not look like it has any FEC adjustment itself. So I guess the question now is will it pick up the FEC set in the body and transmit that?

So now my answer is I have no clue what I am talking about and am going to shut up and sit down now.

dedsen wrote in post #11783397
Leo, are you sure? I do not think they will add like that unless I am not understanding the example.

I have never used the ST-E2 but I would think that since the two 580's have to be in slave mode to talk to the ST-E2 that the FEC you set on them would be ignored or reset by the info transmitted to them by the ST-E2. It would be the FEC set on the ST-E2 that would take precedence over anything set on the camera body.

Here is a quote from the 580ex manual-

Any flash exposure compensation amount, high-speed sync (FP flash), FE lock, FEB
amount, manual flash, and stroboscopic flash settings set with the master unit will all
be automatically transmitted to the slave units.
So my understanding of the above example would that the +1 set in the ST-E2 would be transmitted to the remote 580's and the +2 in the body would be ignored. The +2 set in the flashes would be reset to the +1 that the ST-E2 sent to them. I could be wrong since I do not have the equipment to test it.

Edit:When looking at the manual for the ST-E2 it states that FEC has to be manually set on the slave flashes. It does not look like it has any FEC adjustment itself. So I guess the question now is will it pick up the FEC set in the body and transmit that?

So now my answer is I have no clue what I am talking about and am going to shut up and sit down now.

As you have already discovered, the ST-E2 does not have FEC so whatever is set on the body will be used for the overall FEC that affects all remote flashes. Had the master been another 580EX, then whatever FEC is set on the master would take precedence with the FEC on the body being ignored.

When FEC is set on the individual slaves, that FEC value will also be added to what has already been set by the camera.

But now that I think about it, the ratio set on the ST-E2 (or any master) is actually used to only determine the different in exposure between the two slave groups and doesn't really enter into the picture as far as overall exposure is concerned. So, I'll retract my previous reply and say that the total exposure from the flash in the example above is +4 FEC, not +5, above what ETTL thinks it should be. However, had the FEC amounts been all negatives, then -5 FEC would be correct amount, not -4, below the normal exposure.

Interesting that my question doesn't have a clear answer... the way this works just isn't intuitive I fear...

As far as I can tell the ST-E2 ratio setting sets a ratio (balance) between the flashes, so with no other changes the *total* exposure from *both* flashes remains the same. I don't know how it does this. Does it meter each flash separately (it ought to!), or just crudely set output levels?

The 580EXII allows me so set compensation even in slave mode (up to plus or minus 3 stops) - so I'm guessing this would be locked out in that mode if it was to have no effect? (The 420EX has no manual controls)

I guess the only way to prove this is to take lots of test shots with wild FEC and ratio settings to see which have an effect, and which don't... I was just hoping someone had an authoritative answer or had done some tests already

wibbly wrote in post #11786963
Interesting that my question doesn't have a clear answer... the way this works just isn't intuitive I fear...

As far as I can tell the ST-E2 ratio setting sets a ratio (balance) between the flashes, so with no other changes the *total* exposure from *both* flashes remains the same. I don't know how it does this. Does it meter each flash separately (it ought to!), or just crudely set output levels?

It meters each group separately, (A, B, c) then iirc it meters A+B combined. Group C is always metered on it's own as it is a dedicated "background light" group.

wibbly wrote in post #11786963
The 580EXII allows me so set compensation even in slave mode (up to plus or minus 3 stops) - so I'm guessing this would be locked out in that mode if it was to have no effect? (The 420EX has no manual controls)

FEC set on a slave IS taken into account. So you can set up (for example) a main and fill light on the same group by setting the fill light to say, -2 FEC, so it will always be 2 stops less than whatever the key light will be.

wibbly wrote in post #11786963
Interesting that my question doesn't have a clear answer... the way this works just isn't intuitive I fear...

Ah, but it does have a clear answer. There's nothing random about the amount of FEC that's used for the exposure of each flash.

wibbly wrote in post #11786963
As far as I can tell the ST-E2 ratio setting sets a ratio (balance) between the flashes, so with no other changes the *total* exposure from *both* flashes remains the same. I don't know how it does this. Does it meter each flash separately (it ought to!), or just crudely set output levels?

The 580EXII allows me so set compensation even in slave mode (up to plus or minus 3 stops) - so I'm guessing this would be locked out in that mode if it was to have no effect? (The 420EX has no manual controls)

Each slave group fires a preflash that's used to determine exposure. Each slave group fire in turn, first A, then B and then C. Group C is not used to determine overall exposure, though, just A and B are.

Once the overall exposure has been determined from A and B taking into account the lighting ratio set on the master, the exposure for each of the slave groups is determined based on the ratio. Any FEC set on the master (or the camera if not set on the master) is then applied to each group exposures. The command is given to each slave group to fire at the predetermined level. Each flash then takes the exposure value given to it for its slave group and factors in the FEC that has been set on the flash and that becomes the resulting exposure from the flash.

wibbly wrote in post #11786963
I guess the only way to prove this is to take lots of test shots with wild FEC and ratio settings to see which have an effect, and which don't... I was just hoping someone had an authoritative answer or had done some tests already

There's nothing better than learning from one's own experiences. Learning by doing is a really good thing.