Next summer I'll have to photograph several situation at the beach like sports,families with kids,kids playing and so on.I was wondering what could be a best flash or strobe to take with me.I already have a canon 580 and I was thinking about buying something like a lumedyne or using my canon with a ST-E 2 transmitter to keep the flash off the camera
.I compared the power and either the canon either the lumedyne 400W/S has the same power( both of them need a f16 at 3 meters).I might even consider about buying a powerful portable strobe but I do not think it will worth because the budget of this work is not so high to have an assistant with me.
Any suggestions?
Thank you

If you are shooting with anything but a Canon flash I don't think the ST-E2 transmitter will work. I 've used it allot with the canon flashes and have had many fires, particularly out doors. I'd go with a pocket wizard set up. Works perfect every time. Flash wise there are lot's of choices.
Hensel, several Profoto units, Broncolor, Dyan-lite. Elinchrome Ranger unit, Alien Bee's I think has a battery unit also. If shooting sports (action) you will want a very short flash duration, the only units that will do that is the high end Profoto & Broncolor.

Oh,ok than I will buy a pocket wizard.I said STE-2 because I thought was the right one for canon.Is a pocket wizard compatible with canon?
What does it mean?
I also need an explanation about flash duration:if my camera synchronize at 1/200,so that is the fastest time I can shoot with a flash,what matter having a very short flash duration?

A few comments:

1) There are other flashes that will communicate through wireless E-TTL with Canon equipment, such as the Metz 58. However, there aren't any that have equivalent power and features that don't cost at least as much as the Canon units, I don't think. Sorry.

2) An ST-E2 does in fact cost less than a flash, but if you can possibly afford it, I'd buy another 580EX to use as a master. It will communicate with your current 580EX and fire it as well as providing another source of light. If you don't want it to add light, just reverse it or black it out - it will still talk to the other flash.

EDIT: Actually, I looked at my 580EX, and you can just turn off the flash and tell it to only be a strobe transmitter, in essence turning it into an ST-E2. Nifty, I might fool with that and my 420EX.

3) Probably the cheapest portable AC strobe solution is an Alien Bees AB400 and a Vagabond II power unit. After that, what you spend is up to you.

4) PocketWizards work just peachy with Canon flashes but keep in mind that PocketWizards *do not communicate exposure information.* If you set up manually, that's not a problem, but unlike the ST-E2 or using another 580EX as a master, you cannot use autoexposure if you are using PocketWizards. All PocketWizards do is say, "Flash, go off." If your flash has manual control, you can control the flash output that way, but otherwise, it will just go off at full power.

5) Very short flash durations freeze action better. If your flash is your only source of light, your flash duration is your effective shutter speed. But even if your flash is your only source of light, you cannot shoot faster than your sync speed because your shutter may not be open at the right time.

It's not that it will not be open *long enough.* Very few exposures will be shorter than the flash duration of a Canon 580EX, which is on the order of 1/1000 at full power and goes down fast from there. It's that it may not be open at the *right time.* It gets complicated and it depends on your equipment, the kind of shutter you have, etc. Suffice it to say that shorter flash duration, with total flash output constant, is usually better.

M

I was coming from more of a production level shoot where you I would not consider a canon flash nor would it have near the power needed. If a model is ten feet + away at f11 - 1/200 sec and you need allot of light plus a specular source of a canon isn't the same as a box or other light modifier.

Flash duration is regardless of shutter speed. Shooting out doors in bright day light you need allot of juice. The more juice the the longer the flash duration, the lower the power the shorter duration. A speedotron pack at full power is maybe 1/300 sec ( I'm guessing here but experience tells me it will not freeze action in a studio setting. The high end Profoto & Bron gear will have a flash duration at low power 1/16,000 (again guessing from memory, see the specs online)

I wasn't saying use the pocket wizard with the canon flashes, I was assuming a more production set up not a on camera flash type shoot.