For the wedding environment, does the 5D have noticably greater focus performance over the 20D?
I seem to be having focus problems in those dark environments, was wondering if a camera upgrade would help me (maybe I'm just looking for an excuse to upgrade)...
I have recently brought got the 5D and kept my 20D for backup and motor sport where the drop helps. I noticed the difference when I replaced my glass with fast L glass, not so much the body.
The 5D does have better focus performance than the 20D. However, I don't know that that should be the main factor for upgrading. I finally just learned to deal with the 20D autofocus weaknesses and I anticipate what situations would be problems and deal with them accordingly. I use manual focus or other methods to ensure correct focus. In dim light, the focus assist should help you, or get an ST-E2 just for the focus assist.
Things that can help:
Fast lenses (2.8 or better). Extra focus sensor in the center turns on.
External flash ON THE HOT SHOE not a bracket - it has an AF assist light, but if it's on a bracket it doesn't align with the lens axis anymore.
Get closer - shooting from across the room with a 70-200 makes it double difficult
use the center focus point on a 20/30D as it's a cross sensor
Use canon glass with USM motors, L glass preferably. It does focus better and faster than third party lenses.
Get a 40D is the answer - unbelievebly better focus and faster too.
As to a 5D, it has a better AF system that a 20 or 30D, but it's still lacking in dark receptions at times - a bigger sensor means bigger light box/mirror box so it gathers more light and that helps, but not a whole lot. The 40D blows it away IMO for focus.
The 20/30D with primes drives me CRAZY with backfocus. I KNOW they are calibrated OK, but when I try to focus on something further away with a wide aperture, it will often focus on the background ... but the viewfinder is so small that I can't tell until I get the images home.
Looking forward to a 40D, 6D or 1D Mark III ... (winter is going to be expensive!)
