« on: August 07, 2014, 11:09:39 PM »
First, I would ask the bride/groom. It will flow much more smoothly if they know you intend to shoot around.
Second, I would check in with the photographer. They *should* be more generous about allowing you to get in a few shots as well. As others have mentioned, I wouldn't plan on getting any of the shots that involve setup, such as the bridal party, family, or in the moment cake shots. As a pro, I don't mind if others are shooting, as long as they are not interfering with the shots I am being paid to take.
I would carry two lenses, the 50 and the 100. I would also keep the flash on the camera or in my pocket the entire time. I use the heck out of flash photography and finally am able to use it properly. From a pro's perspective, please do not use the flash during key moments such as the kiss, cake, champagne, or other moments that are there and gone. I have seen my fair share of photos ruined due to someone else's flash firing, rendering a blue hue, and casting horrendous shadows. I do firmly believe in learning flash, however, and would definitely use it for your detail shots taken with the 100L.
I would also focus on where you plan to be. The 100 will keep you at a good working distance if the area is large enough, the 50 will allow for your low light shooting.
As mentioned earlier, shoot for quality over quantity. Make each shot count, and the pro will should be there to care of everything else.
I hope this helps!