Can someone answer this kinda odd flash Q about 420/550?

I have one each, the 550EX and the 420EX. Obviously the 550 will have to stay on the camera for now (or near it) while I use the 420 as my slave / primary flash. Assuming I'm taking a picture of my 3 yr old in a nice big leather chair, and the primary 420 is at approx. 45 degree angle from me towards the subject, what should I set the 550EX manual intensity to so that it produces roughly half the output of the 420? Is there any way to figure this, assuming I wanted a 2:1 from the 420 to the on camera 550?

I'm sure that sounds vague, but hopefully someone with enough flash experience can point me in the right direction. I'm loving the 550 on camera, but am trying to more creatively and effectively use the 420 as a slave.

Thanks for any link or advice on how much I should stop down the 550EX to be roughly half that of the 420! (If it's possible)

Adam

If I understand the question correctly, I think you want to start with the diagram in the 550EX manual on page 63. However, it is describing two off-camera slaves. If you include the 550EX set up for Wireless Master and then follow the A and B slave settings, that will get you close, except that the A slave settings will go into the 550EX and the B slave settings go into the 420EX. The page 65 diagram shows the ratios.

BTW, isn't it a little more traditional to have your main on-camera flash be the main light and let the off-camera flash be the fill? It's OK to be non-traditional if that is what you really want.

---Bob Gross---

Ok I'll go check it out. I guess my concern was around finding diagrams discussing ratios between 550s which wouldn't exactly be accurate since the two have different output power.

Thanks!

Yes, I hear you. The Canon diagrams are not very extensive. First of all, the 550EX's guide number is a little more than the 420EX's guide number, but it is not very much more. Then, I wouldn't let that phase me, since that is only a maximum number. If this ratio stuff works right, and if you stay well within the flash range, then that difference shouldn't be noticeable. Get the 550EX set for wireless master and the 420EX set for wireless slave (which is the bottom switch). Then all of the ratio stuff is around page 63-65 of the 550EX manual.

---Bob Gross---

Ok thanks again. I had no problem getting the 550 to fire the 420, I just need to play around with ratios to manipulate some shadowing. Time to go RTFM!

Adam

For a three-year-old, you'll need a fast shutter.

---Bob Gross---

It is actually better to use the off camera flash as the master and positioned to create the light/shadow pattern you want (glamour, split, etc.) and use the on camera flash as the fill. The fill light is best at the position of the camera lense or as close as you can get to it, so that the fill light doesn't produce confusing shadows. I use a 550EX on a lightstand (Slave B-Key Light), a 550EX on the camera (Master A-Fill Light) and a 420EX(Slave C-Background). I set the ratios (A:B):C to (1:3):-1 to +1 depending on how I want the background to look.
If you use the on camera flash as the Key Light, you can't change the lighting pattern without moving the camera.
Regards,
Scott

I tried to make it clear above that I would be using the 420 off camera as the primary flash, and the on camera 550 as the fill flash, I am just trying to figure out how much to stop down the on camera 550ex so that it is just that, a fill flash but not overwhelming to the 420.

I suppose I could start at -1 on the 550 and bracket it.... hmmm

Thanks for the input though guys!

You can use wireless ETTL ratios as I said above. Set your aperture to whatever you like that gives you the look you like and still meets your distance requirements. I use f/5.6. Set the slave group on the 420EX to Group B, the 550EX defaults to Group A as Master. Then on your 550EX Master enable Ratios>A:B and try 1:2 or 1:3. The camera will then adjust the output of the individual flashes so that they produce that ratio.
If you are going to adjust the output using FEC, keep in mind that in order to set FEC independently directly on each flash in Wireless ETTL, both flashes need to be in the same group. If not, anything you set on the Master will also affect the slave. I learned this the hard way.

Scott

Ok so this is interesting... are you saying that if I stop the 550EX on the camera down to -1 and it's in the same group as the 420, that the 550 will trigger the 420 at -1 as well? That could be my problem.

Now if I put the 420 in a different group, group B, and the 550 is in Group A, as you mention, with the 1:2 ratio, would that mean the 550 (b) will be fired with half the intensity of the 420 (a)?

I'm currently couch-ridden with a ruptured disc (happened last week... first back problem I've had... NOT fun.) but I've got some stuff set up here and am learning all I can while I'm down.

Thanks!
Adam

[QUOTE="Adam Hicks"]Ok so this is interesting... are you saying that if I stop the 550EX on the camera down to -1 and it's in the same group as the 420, that the 550 will trigger the 420 at -1 as well? That could be my problem.[QUOTE]

No. The opposite. If they are in the same group and you set FEC on the 550, the 420 will be un affected. If they are in different groups, they will both be affected the same. Sad but true.

[QUOTE]Now if I put the 420 in a different group, group B, and the 550 is in Group A, as you mention, with the 1:2 ratio, would that mean the 550 (b) will be fired with half the intensity of the 420 (a)?[QUOTE]

That would require a 1:3 ratio. A one stop difference (1/2 the light) is a 1:3 ratio. Sad but true.

Feel better soon. If you read the 550EX manual about 3 times it starts to make sense.

Scott