I do quite a few parties and suchlike. Everything is dependent on the available light.
Usually working in Manual or Av mode, I tend to use f/4 or thereabouts as it separates subjects nicely from the background. If doing a group shot with some depth to the subjects, I'll take the aperture to f/5.6 or even f/8 if there's enough light. If not, I'll bounce the flash off the ceiling to help things along, and jiggle the ISO accordingly.
Key thing is to keep the shutter speed up. I generally go for 1/125th but can go slower on my IS 24-105 as long as the subject isn't moving.
If there's low light and I dont want to use flash, I'll put my 50 1.4 on and set it fo f/2.0 or so, and adjust the ISO to get a suitable exposure at a decent shutter speed.
I'll very rarely use direct flash, preferring to bounce it to get a softer light. This works well with a light ceiling but is rather ineffective outside due to the lack of ceiling, or in very high or dark ceilinged rooms. Using ETTL with the flash allows even bounced flash to expose nicely as the camera does the pre-flash, meters from that and then gives you the correct flash strength.
Also, I'll tend to ensure I get enough of the background exposed to give some context to the setting and avoid the images looking over-flashed (very bright subject, dark background). To do this I'll expose the scene manually at about 1-2 stops below "correct". The bounced flash then lights the subject and the generally distant background is still exposed enough to avoid that dreadful flash fall-off effect.
In this example, if I used direct flash in P mode, the background would be black and the guys in front would look very bleached.
Also, when everyone is a bit lashed I like to do some 2nd curtain sync flash stuff with a slow (1/5th) shutter speed. Great fun and you get some very cool images.
Depending on the type of crowd you are photographing, getting in really close at whacky angles with a wide angle lens works really well.
Cheers
Tobers
