Alright guys, I need to take pictures at reception and all i have is a Canon 30d, 50mm f/1.8 and 18-55mm f/3.5-5.6 and a 430ex flash with a sto-fen diffuser. I tried using a diffuser at one of last receptions with high ceilings and it was dark and I did not like the results. Please help me get the shots right this time. I am freakin' out. Thanks ahead of time.

There's nothing wrong with direct flash. You can even be fancy and hold it off camera in your free hand.

Drag the shutter, use ISO 800 or 1600. I would recommedn a 2.8 lens, if budget is a concern, Tamron 17-50 2.8 is an alternative (make sure to baby the lens, their customer service is very picky).

You can also try renting a second lens, put it on a tripod or something and use it as a slave. When you cross light like this, it works as a seperation light.

What do you mean their customer service is very picky?

Going off camera can be very nice. I still like to diffuse the light though, leave the stoffen on and shoot direct through it. Opening up, slowing down and pushing up your sensitivity will help open up the room as well.

One thing to remember, when you go off camera be mindful of where you are placing your shadows and the angle of approach you are using. Going too far to the side might block your main subject in someone else's shadow. Just a matter of getting used to the feel of the process.

Good luck.

When I diffuse my flash with the sto-fen, I get a harsh shadow when using it direct? I do not know why and I thought purpose of the diffuser was to prevent this from happening?

If I recall correctly, the sto-fen is supposed to be aimed at an angle to diffuse light more effectively, and not shot head on. Even so, it'll be a small light source, it'll inevitably cause shadows. A light source has to be large to be really diffused. But shadows aren't necessarily a bad thing, you just have to get them to be more directional via an off camera flash http://strobist.blogspot.com/2006/03/light...hard-light.html

are there any lights in the place?

often i'll drag my shutter to like 1/13 of a sec with iso 640 or 800, shoot my flash (thru a stofen) direct on ttl, but dial it down to like -2/3.

this will give you enough direct light to freeze most motion at the point of focus but give enough drag to soak in what light is available.

LISTEN UP, i only capitalize to bring attention to this. In this situation (and ohio has plenty of high ceiling, dark reception halls) i wil do what i describled above, then i'll drop my level to find a lamp or whatever light exists in the room and i'll move with the couple to make sure i keep them in line with the light that is behind them, even a small lamp, a candle, dj light ANYTHING can liven the background so long as it's light (i've even had exit signs work for me, it's a cool blurry red light in the background that livens up the image) try this. often i take photogs in training with me, we'll be standing side by side shooting the same thing, my pix look great, theirs look bad, we compare settings and they are like 1/45s or something like that or often 1/60 as a default to A mode. long story short i'll set their settings, tell them to line up the light nad whala, amazing shot. i find this to be the number one technique i'll use to liven up places without using off camera flashes, assistants etc.