.... I've got a Canon D30 and a Canon 300D that my wife and I enjoy
using for mainly birds/wildlife....

We've been using a Canon 75-300 usm (sometimes with a 1.4 extender)
for close ups of birds etc...

I've just got a Tamron 28-300 XR and at full 300mm it gets nowhere
near as close as the Canon at 300mm.... Even with the 1.4 on it's only
just about the same as the Canon wothout the 1.4 on - why should there
be such a difference ????

Surely 300mm is 300mm no matter what make of lens..... ?