Once more: 20D with 580EX and 2x 420EX flashes

[mwillems]

Once more: 20D with 580EX and 2x 420EX flashes

I apologise! I have read all the manuals, the guides, the link from here and the archives here as well - all very very useful. But I just need to hold my understanding by you all once more to see if I actually understand how Canon E-TTL2 works on the 20D with 580EX and 420EX speedlights. Sorry!

I have the following setup:

- 20D with 580EX as master in group A, aimed at the subject
- 420EX slave on light stand in group B, aimed at subject's side
- 420EX slave on light stand in group C, aimed at background

So my two questions:

a) If I understand this right group A and B illuminate the subject and group C always blows out the background? I guess group C is not taken into account during the preflashes?

b) The ratios are SO badly explained in the manual! What can I set?

- A:B ratio?
- or (A and B) : C ratio?
- or A : (B and C) ratio?
- Both, so that I can effectively control A:B:C in any ratio I like?

Am I missing or misunderstanding anything else?

Many thanks for bearing with me - I know I am being thick.

Michael

[CyberDyneSystems]

From "weak" memory..

..the ratios are simply A: is strongest, B: is in the middle, and C: is weakest.

[mwillems]

Not sure I get that: on the 580EX, I can set A:B in one menu and I can set A:B C (or is it A B:C) in the other. And if I set A:B, C does not work, that much IS clkear from this appalingly written manual.

[mbze430]

the A, B, C are groups. You can have multi flash heads in one group.

For example. I sometime use 2 580ex as a main light. That would be set for A. Than I would have a 2 580ex set a fill; B Group, and 1 C Group 580 for hair.

By default you can control lighting ratio A:B:C, if you are using the 580EX as master. You can do the same with the ST-E2, but you have to manually set the C group in Manual mode, and no E-TTL. In this case you will have to correctly meter the group C flash heads.

[CyberDyneSystems]

Try putting both 420s in B: group?

[mwillems]

All that sounds like Greek to me.

SITUATION:

I have a flash in group A.

I have a flash in group B.

I have a flash in Group C, which I understand is the background lighting flash group.

QUESTION:

So, using the controls on the 580EX, can I set the ratio of A to (B and C), or (a and B) to C, or A to B to C?

Sorry to be thick - I am an engineer but these manuals are dismal..!

Mike

[mbze430]

it is (A:B) C. Page 41 in the 580EX user manual this is if you want E-TTL

A:B:C. Page 42. You set all of them to manual. Will need flash meter.

[RichardtheSane]

This is why I decided to invest in studio flash - I read the 550ex manual! :)

(Sorry I couldn't be any help)

[mwillems]

it is (A:B) C. Page 41 in the 580EX user manual this is if you want E-TTL
A:B:C. Page 42. You set all of them to manual. Will need flash meter.

But sorry, I read that, and I do have a science degree - and yet I do not know what (A:B) C means. Ratio of A to B times C? Ratio of (equal A and B) to C? AM not trying to be thick.. an really trying to understand!

Mike

PS yes read the manual

[DaveG]

Once more: 20D with 580EX and 2x 420EX flashes

I apologise! I have read all the manuals, the guides, the link from here and the archives here as well - all very very useful. But I just need to hold my understanding by you all once more to see if I actually understand how Canon E-TTL2 works on the 20D with 580EX and 420EX speedlights. Sorry!

I have the following setup:

- 20D with 580EX as master in group A, aimed at the subject
- 420EX slave on light stand in group B, aimed at subject's side
- 420EX slave on light stand in group C, aimed at background

So my two questions:

a) If I understand this right group A and B illuminate the subject and group C always blows out the background? I guess group C is not taken into account during the preflashes?

b) The ratios are SO badly explained in the manual! What can I set?

- A:B ratio?
- or (A and B) : C ratio?
- or A : (B and C) ratio?
- Both, so that I can effectively control A:B:C in any ratio I like?

Am I missing or misunderstanding anything else?

Many thanks for bearing with me - I know I am being thick.

Michael


OK lets start at the beginning. First the 550 is the Master and will default to Group A if you leave it alone. Then take one 420. This needs to be set to Group B. For the moment lets leave the second 420 out of it.

For portrait setups you would want your Main light at 45 degrees to the subject. Although you can put the Main wherever you want, this is the best idea for a classical portrait. Then you need to have a fill flash and that MUST be within 20 degrees of the camera position so you insure that both sides of the subject's face gets the same amount of light.

I use a Stroboframe Pro-T bracket and it holds the 550 directly above the lens. It also is in a great position to "transmit" the TTL signal to the Slaves. To be clear: The 550 is the Master and it is the A Group flash. But it is also and MUST BE the Fill light not the Main.

Now put the 550 on Master with the switch near the hotshoe on the bottom of the flash. Push the Sel/Set (S/S from here on) and scroll though until you see OFF (ratio), then use the minus button (-) to change it to RATIO A:B. Once this is done you will have a line on the 550's LCD display that goes from 8:1 on the left to 1:8 on the right.

In spite of the fact that a classical portrait lighting is 3:1 YOU MUST select 1:3. I think that this has to do with which flash is the Master and which is the Slave, but select 1:3 PLEASE!!! Now your 420 is the Main light and will output about a stop more light than the 550. THAT is a 3:1 lighting ratio and is what you want. You can mess around with the ratios to see what each setting will do by pushing the + or - keys. Try it. 1:4 or 4:1 might be better and with digital practice is free!

Now you can add the third flash the C group (and in this case) 420. Look at the 550's LCD. You should see RATIO enabled and then A:B. Push S/S and RATIO A:B will blink. Keep pushing S/S and it will cycle through Channel, ON, a flash compensation control, the flash sensor options, and then to ON RATIO A:B. If you push the MINUS (-) key you will now see ON RATIO and then A:B:C. Ah ha we've gotten to C!!!

Keep pushing the - key until you only get RATIO C showing. Along with that should be a flash compensation control that should be zero (0). You could leave the C flash at 0 and it will output the same as the B flash. Or you can ask it to over (or under) expose the B flash by whatever you'd like. For a hair light you might want it to be over by a stop. Or you might want to shoot a little light into a dark area of the background and in just enough of an amount to preserve some shadow detail. That's up to you.

On the 420's you must have the same Channel selected as on the 550 and the 550/420 instruction book is clear enough on that topic. And of course you need to have one 420 on B group and the other on C. I have small pieces of tape on my 420's so each is clearly marked and since I always have one on B and the other on C I'm not messing with that in the field.

If this isn't clear feel free to contact me.

[mwillems]

That is very clear - many thanks

One question though: the 580's manual states that is a:B ratio is set, C flash may not be use. Did I misread that?

M

[DaveG]

That is very clear - many thanks

One question though: the 580's manual states that is a:B ratio is set, C flash may not be use. Did I misread that?

M

If you have the flash ratios reading A:B then there won't be any response from a C group flash. You need to see A:B:C for the C group flash to be in the game.

But you can have any number of B group flashes (and C's as well). The only direction that the communication travels is from Master to Slave. The Slaves do NOT talk to the Master, nor to other Slaves. So the Master speaks and one or two (or twenty) Slaves fire if they are all B group, since the Master has no idea as to how many Slaves are listening.