ETTL vs Manual with canon flashes

[sweetypie925]

I may have posted this before but I am confused when it comes to using flash. I would mosty like to take some indoor and outdoor portraits but confused whether I should use my canon flashes via ETTL or on manual. I have a 580ex, 430ex and those cactus triggers. I understand that to have ETTL I have to have the 580 as master on camera and the 430 as slave off camera. The 580 then can be shut off completely or used for fill right? If I wanted to have them both off I would need one of those off camera shoe cords right?

Now to go manual I am really confused. I can get them both off camera but need a light meter? If I don't have one,how do I meter the scene and then how do I get my flash output correct. Can someone walk me throught each of these scenarios and why/why not I would want to use them, like give me examples of when one would be better than the other?

[Curtis N]

With the equipment you listed, your options are:
A) 580EX on the hotshoe, 430EX off-camera & fired via the wireless flash system as described in the 580EX manual. You can use E-TTL or manual flash mode. The 580EX can fire or not (used only to trigger the slave). Limited distance between units (especially outdoors) and usually line-of-sight required.
B) 580EX off-camera, triggered via PC cord or Cactus set, 430EX triggered by 580EX using Canon wireless flash system. Manual flash mode only. Same limitations with distance and line-of-sight.
C) Both units fired off-camera via a separate Cactus receiver on each unit. Manual flash mode only. Distance limited by strength of radio signal, no line-of-sight issues.

When using manual flash, a meter can be quite helpful but not essential. Understanding guide numbers (http://photography-on-the.net/forum/showthread.php?t=208520) and the relationship between aperture and distance helps greatly.