If I read your question correctly, you are experiencing the results of flash illumination gradient in the scene.
Back to flash fundamentals for just a moment.
Suppose that you are focused at exactly 10 feet from a person in a crowd that extends from 5 feet in front of you to 30 feet in back.
The TTL flash will control the flash output so that the person in focus gets exactly the right amount of light ( assuming you are using direct flash pointed at the subject )
What happens to the foreground people? Well, they get 4 times the correct exposure for illumination.
What happens to the background people? The people at 30 feet get 1/4th of the correct exposuer.
This all happens as a result of the light intensity varying as the square of the distance from the light source. The foreground folks get 10 squared divided by 5 squared and the background folks get 10 squared divided by 20 squared. The 5 and 20 are the distances from the 10 foot focus distance selected.
So ... it doesn't matter what the power of the flash used is if you are using direct illumination ( flash pointed straight forward ). No amount of power will fix this.
There are two choices, the first was mentioned earlier. Get additional flashes and position them to provide a more even lighting over the distance needed. You get a lot more control of the directionality of the light, the uniformity of the light, etc. You also get a lot more cost - 2 - 3 times more cost for the extra units. It does ( or can ) work great.
The second choice is to use bounce flash. That is, point the flash head up towards the ceiling so that the crowd is more nearly the same distance from the light. I'm not familiar with the 550 unit you have but others have referred to it as quite powerful so you may already have enough illumination. You will want to tape a reflector to the back of the flash head so that all the light that would normally go directly up is reflected forward to help in the foreground. Set the head to a 45 degree angle and make sure through camera / flash settings that the unit can provide full power only controlled by the TTL system. If the ceilings are not too high, and unfortunately museums tend to have quite high ceilings, the results should improve substantially. You'll have to experiment to see if this will work in the venue you describe.
Hope this is of some help.
James
At 12:24 PM 9/8/2006 -0700, you wrote:
Hi PF members,
I am looking for a new on camera flash unit - one that has quite a bit of power.
I've been using the Canon 550 OEX. Much of the use will be photographing functions in a gallery/museum, which is rather dark inside. The EOX just doesn't through light far enough.
Any suggestions would be appreciated.
Thank you.
Marilyn
