So at the moment I have a Tamron AF 75-300mm F/4-5.6 lens, and its all right but its defiantly a budget lens. Ive found that its fairly sharp at f/9 - f/11 and about 250mm zoom. However, I would like to extend that range and don't have much of a budget so I'm thinking about getting a teleconverter. Would the image still be sharp if the lens is at 250mm but with a 1.4 teleconverter attached? I've heard that TC's can negatively effect AF with certain apertures, I'm wondering if that will effect my lens. Also I've read that they can degrade quality but I have seen test shots with a 1.4 and I didn't see much of a difference personally. Finally, are the Tamron TC's any good? The test shots I've seen were with a Canon TC and havn't had a chance to see any examples from a Tamron. So do you guys think a TC is worth the purchase?