Night photography??

Perhaps meanwhile, you could practice some indoor photos with available lighting to get a feel for using high ISO settings. You will need to keep the shutter at a reasonable speed and will probably have to use the lens wide open to maximise the amount of light for correct exposure.
Good luck and I hope it all goes well!

Thanks Ian! Yes that's what I'm doing at the moment
I hope it goes well too!! Honestly it seems like a nightmare right now!

To get a rough idea on the settings:
1. Set your iso to auto
2. Set Cam to Manual
3. Select widest aperture for your lens
4. Select shutter speed
5. Take the shot
Bring up the pic in camera and see if it's acceptable. If it is note what iso the camera selected that should be your starting point. If there's too much noise, you can back off the iso or lower the shutter speed. If the pic is too dark try increasing the exposure compensation a stop at a time.

garys1 wrote in post #9728094
To get a rough idea on the settings:
1. Set your iso to auto
2. Set Cam to Manual
3. Select widest aperture for your lens
4. Select shutter speed
5. Take the shot
Bring up the pic in camera and see if it's acceptable. If it is note what iso the camera selected that should be your starting point. If there's too much noise, you can back off the iso or lower the shutter speed. If the pic is too dark try increasing the exposure compensation a stop at a time.

Really? I don't trust auto iso that much

How can I tell what iso the camera selected?

AudibleSilence wrote in post #9728110
Really? I don't trust auto iso that much

Neither do I but at least it gives a starting point rather than guessing.

Lulula wrote in post #9728175
How can I tell what iso the camera selected?

When you view the image, press the info button on the back of your camera...it'll show you all the settings for the picture.

put a two or three layers of the thin plastic bags (that you get from most supermarkets, chain stores, etc when you shop ) over the top of your flash, to spread the light out a bit, and cut down on burnt out cheeks, chins, and noses...

also shoot in as high a iso (800 to 1600), so that the background won't just be black past the people, and be in shutter mode, set to 1/125 - 1/250th this way the camera can tighen the fstop if your looking into a suddenly bright scene.

keep in mind that you can't take any group shots with your fstop wide open, as you have very little depth of field, so the peopl on the ends wil be blurry.. you would need to tighten the fstop to fix that and I doubt you will have the light for that.

A note about the Auto-ISO.... on the 50D, it will only go up to 1600. Depending on your lighting, you may have to go beyond that.

emtp563 wrote in post #9715055
One thing to keep in mind is camera shake, if you're zoomed to 200mm, you'll need a shutter speed of at least 1/320 to avoid camera shake. Adjust your ISO accordingly to keep the shutter speed > 1/320.

18-200 has IS, no?

Your profile doesn't say where you are, but if you're in the US, you can rent from eg. lensrentals.com. You also might be able to buy something off craigslist, use it, and sell it again for the same price if you don't want to keep it.

garys1 wrote in post #9728094
To get a rough idea on the settings:
1. Set your iso to auto
2. Set Cam to Manual ...

The OP is using a 50D. The 50D in manual mode with auto ISO set will not shift ISO to maintain exposure. With those settings, the camera defaults to ISO 400.

You're not looking to publish these in National Geographic, right? You just want halfway decent snapshot quality pics to commemorate the event?

Set everything to auto and shoot away.

Otherwise, you may have an aneurysm trying to learn the finer points of flash photography between now and then.

Think a long time about using flash for an event. Be prepared for anything. There might be more available light for the opening ceremony than is anticipated but it is likely to be uneven. Get as much information about the ceremony as possible. Your positioning could be critical. Practice at night, an athletic event is good or in a parking lot would be better than nothing. You might even get lucky and shoot something where your event will occur. Practice, practice, practice. Absolutely no flash during competition.

anthony11 wrote in post #9729543
18-200 has IS, no?

Yes it does have IS and it works pretty well. That would help a lot for low light shots on still subjects.
The 18-200 is not a bad lens but I would think a faster lens would be a better option.
I use the 17-55 f/2.8 for a lot of low light photography keeping the shutter speeds over 125th. There will be some noise but after some NR and resizing it is invisible.

Hum, tripod shooting a sports event, that would be interesting. You will at the very least need a 2.8 lens, with IS. Flash fill might be good also but not sure since we can't see the event lighting from here. I shoot soccer and football games at night and have not ever used flash for them (don't think the coaches would like that either, have you ever seen a flash go off during a college or pro football game? Come to think of it, I haven't seen a tripod used at one either). A monopod might be handy especially for a long event. You will want to shoot pretty much wide open for being able to use as low of iso as possible. Don't plan to capture the arrow in flight without a flash or strobe, your exposure should be set for the drawback pose and the resulting target hit.