Je suis en attente de cet objectif (difficile a l'avoir celui la) et je suis tombé la dessus:

Probleme sur le 70-300 IS USM :

Dans l'article suivant ( http://minilien.com/?iUqOYyXhWU ) certaines personne evoque un probleme avec cet objectif.

>Nathan G , jan 24, 2006; 01:02 a.m.
>Disappointed, I am planning to return my new EF 70-300 IS USM f/4-5.6 tomorrow (as long as B&H
>cooperates) because it suffers from a significant loss of quality when on its side (on my XT). I didn't see
>much discussion on this forum of this problem before I decided on the 70-300 over the similarly priced f/4L,
>so I thought I'd mention it for any who were not yet aware and who were making a similar decision

Alors pour ceux qui l'on deja, pensez vous avoir rencontré un probleme de mise au point, a la plus grande focale, en mode portrait ?

A+