okay. all I want to do is buy a flash that I can use on the camera instead of the built in flip up flash, but also take it off the hot shoe (wirelessly) to use as a single flash. I'm too noob to be using multiple flash units/ wireless units. Also, does the 603 transmitter unit need plugging into the camera or does it just work through the hot shoe? I'm just getting confused between master and slave and the whole ttl thing. I would like the TTL functions on and off the camera as I'm new to flash photography and would prefer the camera to adjust the settings for me until I become more confident.
Ok, so TTL stands for "through the lens", but for the purpose of understanding what it does for flashes, it might as well be "talk to lamp" -- it's what lets the camera communicate with the flash. This affects metering, so the camera knows it's got some extra light it can throw on the scene, zooming (so the flash zooms with your lens), and exposure compensation (you can adjust the output of the flash up or down right from the camera).
If you want TTL (it sure is handy, so I'd recommend it), start by picking a flash unit that does TTL. I know the 565 and 568 support TTL; the 568 adds high-speed synch (HSS), which will let you use the flash at shutter speeds faster than 1/250. Apologies, btw - I mentioned "565" in my earlier post, but I meant "568" -- I fixed the post. Other than HSS support, the 565 and 568 are pretty similar.
Next, if you want to take the flash off your camera, you'll need a pair of triggers. High-end cameras have triggering built in, but the 350d doesn't. Between the 603's and the 622's, only the 622 supports TTL. Again, I've had good luck with it. Personally, I'd start with the 568 flash and the 622 triggers -- they'll be plenty to keep you busy for a while. If the 568 is too pricy, the 565 would be a decent option, but you'll give up HSS. I don't use HSS a ton, but when you need it, it's nice to have.
I'm not sure if this will help at all, but
I wrote up a bit on strobes a while back, and there are a couple photos in there that might help you. The first section talks about HSS a little, in case you're interested, but the very last photo shows both a 622 and 603 trigger on my 7D and a 603 with my manual flash on the right. The 568 is sort of cut off on the left -- only the mini-softbox (sold separately) is visible.
I also attached a photo below -- in this case, the 568 flash with 622 trigger are on the left, and the camera has a 622 and 603 on the hotshoe. In this case, the 603 is used *only* as a remote trigger -- hence, the cord running to the left side of the camera. The cord is needed *only* for remote shutter actuation. I'm using the remote shutter in this case because the tripod arm is extended way out, and I didn't want to move the camera by pressing the shutter myself.
