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| p.1 #3 · New to multi-flash...550EX master to a 420EX? |
Chuck's instructions are generally correct, but note that he is showing a 580ex, which has slightly different controls. I use a 550ex, but don't have it with me, so I will try to translate from memory.
The "mode" button only controls the flash mode, so hit it to cycle through the settings until you get TTL.
And on the 550 the "zoom" button (I think) only controls the zoom of the flash. For your off camera flashes you would set this to something relatively wide if using a modifier, or to cover the desired lighting area if using bare. For on-camera fill (as in the situation Chuck described) you can put it on the auto setting so that it chooses the zoom based on your lens (but I don't think it takes into account the crop factor) or just set it manually.
So to turn on ratios you hit the SEL/SET button. This basically cycles through all settings (Flash exp comp -> Flash bracketing -> Ratio -> Channel -> Master On/Off). The setting that is flashing is the one you are changing. So push SEL/SET until you see Ratio. Then push the + or - button until you get the type of ratio you want (off, A:B, A:B:C). In this case you want A:B. Hit SEL/SET again.
Now that ratios are on (stuff should still be blinking) you can choose the ratio. Use + or - again to choose 1:2 for Chuck's example. Press SEL/SET again.
At this point you are done. I think maybe it cycles back to the main loop of options, so something may still be blinking, but that's ok. You don't have to make it stop blinking to take a picture.
To answer your question, a group is a set of flashes that all either a) produce the same brightness for their illuminated objects (if in TTL) or b) fire at the same manual power level (if in M). As mentioned, you can only operate in TTL with your 420.
So if you want to be able to control flashes independently, you need to put them in different groups. If you have a bunch of flashes, you could put, say, 3 in group A, 1 in group B and 1 in group C.
The channel setting allows you to choose which slaves are controlled by which master. Useful if you are in a room with other photographers. But you basically always want your flashes all on the same channel.
Oh, and I think there is a 550ex manual that can be downloaded out there somewhere. Hope this helps.