Hi guys!

In two weeks I will be shooting a relatives wedding with three 7d's. I am a little concern in regards to getting critical focus with these cameras since you have to do it manually on the go. I really shouldn't have a problem during the ceremony since everyone will be kinda still, but I am worried about the reception(people moving around, dancing).

Any tips on how to achieve good focus?

What are you guys using to achieve good focus?

Thanks.

If you want the extreme DOF, Z-Finder with follow focus is how my best results happen.
If the shot doesn't require it, expand your DOF a bit by increasing the f-stop to somewhere around 10-16.
I've used that when I have too many other things going on to deal with manually focusing.
Since you have a 7D, you could also use an external monitor.

All shots do not have to be shallow depth of field, for the shots where you want great focus choose a wide angle lens and stop it down to f8 - f16, you will have most of the scene in focus allowing you to move. Just remember to keep a minimum distance away from you nearest subject.

On a 24mm lens to give an example, if I focus at 5 feet using f16, the depth of field ranges from 2.5 feet to infinity.

A good point is to know how much light you will have on the wedding. I shot one a few weeks ago in a church using a 17-50 2.8, a 11-16 2.8 and a 70-200 2.8 and I had to shoot everything on 2.8 and 800 - 1000 iso. Sometimes is very difficult to control the DOF. I was afraid to get a noisy picture by using a higher number. A good advice is a follow focus and lots of practice, of course, and if you're under the sun an LCD viewfinder is a must. But mainly I think is practice pulling the focus. Lately I'm trying to film for some company a horse galloping towards me with the 7D and is really difficult!! I'd need some advice too! :)