J.A.F. Doorhof wrote:
You are absolutly right but some people can't pay for the canon lenses like myself

.
I found the Sigma AF 135-400 APO Asph on
www.photozone.de
this one is tested a 3.21 while the Canon LIS is tested a 4.48.
I'm no professional so I think that I have to start slow.
The standard Canon EF 75-300 I use now is adequate but in no way enough to keep me entertainent for the next year.
Greetings,
Frank
Do not depend on Photozone too much. It is still a popularity contest with most people rating their lens against their own subjective standards rather than against a common and known standard. I made entries for my own equipment there to look at the questions, and they expect those who respond to know what "professional" standards are. The only control is that the answers are reasonably internally consistent and not too far outside the bounds of what other people say. These limits only serve to reinforce the biases rather than to correct them.
The Sigma 135-400 APO earned a 2.6 on Photodo, which is based on objective testing of MTF curves. Your 75-300 did better at 3.1, and that lens has weaknesses as you know. The Canon 70-200/4L that Paul mentioned was rated 4.1 by comparison. The 70-200/4L is not nearly as expensive as the faster L lenses, being only about $600. If you need a longer lens, get the 1.4 teleconverter to go with it.
You are right to start slow. But starting slow means sticking with quality and expanding your telephoto range slowly, rather than buying several cheap lenses that eventually you'll want to throw away. Getting the 70-200/4L, which is only a little more expensive than the Sigma you mentioned, is starting slow.
Starting fast would be getting the 70-200/2.8L IS plus the 100-400L IS.
Take small steps, but take them in the right direction.
Rick "who himself traded the 75-300 for the 70-200/4L" Denney