I've discovered consistent focus problems using Rebel XSi + 430EXii + Tamron 28-75. I confirmed this is a common problem which occurs when the Speedlite's AF-Assist is enabled. Some have suggested ...
The IR AF-assist beam on the Canon Speedlites (I have a 430 EX II) doesn't seem to come on when the DSLR (I have the EOS 7D) is in 'AI Servo' AF-mode. It works fine if I'm in one-shot mode (comes on ...