My question is: Since the f-stop is a "locked" f-stop, would I only have to adjust the aperture? I am under the impression that the flash would eliminate the need to adjust to a higher ISO setting, and if enough light is present at that lens' speed, I shouldn't have to drop my aperturs setting below 100, so I would eliminate alot of the possibility for a blurry picture due to any slight movements. Am I correct in my assumptions?????
Any explanations is greatly appreciated.
I don't mean this in any mean way, but you seem to be in over your head on this one. A wedding is definitely not the place to learn how to use your camera and gear. That being said, let's see if I can try to help you out here...
1) 'Perfect' exposure is always going to be based on 3 things: ISO, aperture, and shutter speed. The constant aperture of the zoom you rented still means you're going to have to adjust the 3 things I listed. Granted, I'm sure there are modes on your camera that will help you not have to think about setting one, two, or even all three of those settings. It just depends on what mode you shoot in. Just make sure your shutter speed is fast enough so that you don't generate blur from your own movement. Blur due to your subject movement may be desirable based on what you're trying to do, but usually you'll want most shots sharp, off course.
2) A flash does not necessarily mean you don't need to worry about the ISO. It all depends on location, present lighting, and what kind of feel you're trying to accomplish with your photos. If you've got the gear in hand now, take lots of practice shots now and see how the flash can alter the look.
3) If you can, bounce the flash. But this really depends on the venue and if there's anything good for you to bounce the flash off of. Direct flash can be harsh and ugly, but may be the only way to light a subject. If you've got the time, learn how to control flash exposure compensation.
4) If you haven't held it in your hands yet, be warned that the 70-200 f/2.8 zoom is going to be heavy.
5) Carry extra batteries for the camera and flash! Carry extra memory cards too.
6) Learn which modes of your camera will try to properly expose for the subject or for subject and background when using a flash. If your camera is like Canon, then Av mode will try to expose for the background as well, while P and Tv will expose for just the subject.
7) Some tips: don't be afraid of higher ISO speeds. Just be aware of what ISO on your camera produces too much noise and try to stay away from it. Depth of field at 200mm at 2.8 is narrow, so keep that in mind and adjust accordingly. You're the photog, so don't be afraid to get into the action or tell folks how to pose when doing posed shots. You can always turn your camera! Not everything has to be shot horizontally or even vertically! You don't always have to be standing to take a photo -- get down on a knee if it makes the photo look better. Get low when photographing just kids. Have fun and relax.