Banquet Photography

Without knowing the camera model, it's impossible to answer.

How did you end up with soft images when using flash? If you're properly using flash, that should never been an issue, unless you're trying to get soft images.

I don't see how the body could make a difference. If your flash is powerful enough, the body (and the lens) should not be an issue with softness, only settings that you use.

Were you using focus assist from the flash? It is only available if you are using One Shot focusing. With it, given your lens can focus accurately, and you have good focus technique, you should have sharp images.

If you were attempting to focus in low light using AI Servo (no focus assist available), with an f4 zoom, I can see why you'd have soft images.

Oops i will be using a Canon 7D with the Canon 24-70mm f/2.8 lens.

I'd give the same answer. Even with an f2.8 zoom, no focus assist from the flash is asking too much in low light.

So--were you using focus assist?

@ Nadine Ohara - I don't think i was using the focus assist option. Thank you I will try it.

Seems that this time you will have a better chance to produce sharper pictures.

What camera body you use matters a lot, since possibly you could afford to use higher ISO. Your flash will recycle faster and have longer range possibly providing more light for distant areas where the ambient light could possibly contribute more to the softness, also you could possibly afford smaller aperture and get deeper focus area.

Your 7D will do fine.

Just keep in mind that auto focus assist light from the camera may have limitted range, but focus assist lamp from an external flash should be sufficient in most cases.

Thomas, your question is so open ended as to make it pretty difficult to give some specific advise and guidelines. The focus assist function has limited range and won't guarantee you sharp shots. We need to understand the geometry of room, how close you can get to your subjects, type of ambient lighting, time of day, etc. Are you, for example, allowed to use supplemental lighting, or off-camera flash setups? Are you doing any formally posed shots or just capturing the banquet as it happens?

Focus assist, though useful, won't be your cure-all. It will not work in every situation. Sometimes even with that feature, your lens might not gather enough light to focus by. You may want to consider a fast prime lens. My 50 f/1.8 has brought me out of many a jam in extremely low light. On a 7D it may possibly be too long. I use it primarily on my film and 5DII cameras.

Please share more detail so we can give you proper guidance.

I was thinking the same thing Frank. If the last time Thomas was using a Rebel at a high ISO, the shots could look very soft due to grain/noise. The 7D should be fine as you suggest.
Also it is easily possible to get soft shots when using a flash, if you have the shutter speed to low and the subjects are moving, you'll get a 'ghosting' and soft results. Some of the ambient light will be captured as well as the flash light.
As Mark suggests, a remote light would be best to fill in darker areas that are too far for the flash to fill in or focus assist to work. For example, if it's a long table and you are at one end, the near areas will be bright and the further areas will be progressively darker. A second light would make a big difference in that setup.