Which lens to use?

I will be shooting my daughters birthday party in a few hours and was planning to use my Tamron SP AF XR Di 28-75 f2.8 lens for the first time at a party; I normally use my Canon EF 20-35 f3.5 – 4.5 for its wideness on my 10D. However using the Tamron the other day I noticed that it does not pass focal length information to my 580ex flash. When using flash I usually set my shutter speed to 1/200 and adjust my aperture between f4 – f10 and let the focal information / aperture information adjust the flash exposure accordingly. Based on the fact that the Tamron will not pass the focal information to the flash should I scrap the idea of using the Tamron for this party and go with my trusty Canon lens? Thoughts please?

What makes you think that the focal length info is not being passed to the flash? What mode were you shooting in?

manul mode on camera and auto on flash, and the display on the flash doesn't display the folcal lenght as i change when i zoom in and out

ok, I feel like an idiot now, I tested it again, and now I see the information on the flash... still a little worried now...

Is the flash pointed directly ahead or upward?

maye that's it, the other day I was bouncing, today straight ahead

sure enough, when bouncing it doesn't show the informaion, but straight ahead it does

Very good... my brother-in-law has a Rebel XT and he regularly forgets (or is too lazy) to tighten down the flash... when that happens, the flash doesn't seem to flash to full brightness probably because the connection points are not perfectly lined up or not making a good connection.

I learned that with the EX 580, when pointed upward for indirect flash, no distance is shown, but you can set it for a specific distance via pressing the zoom button then rotating the dial to pick the distance. With the EX 420, when pointed upward, it automatically to 50mm.

Flash was tight, when pointed up for a bounce flash focal information did not show up, but when pointed straight ahead it does.

makes since... guess the flash wants you to tell it how far to bounce...

just solved the lens delima anyway, my wife is going to bring the 350d with the 20-35 and I am going to bring the 10d with the tamron... just didn't have enough room in my small bag for both lenses

Have fun shooting at the party... young kids are pretty fun to shoot. And the parents of the others always seem to enjoy seeing great photos of their children. With the Tamron, you should be able to get some great candids.

Thanks for the help and the encourgement, I will post some of the photos later

When you're using an EX flash in either bounce or master/slave mode it doesn't zoom automatically, just zips to wide and stays there.