I've been using a canon ef 75-300mm usm lens on my 30d. It's not the best lens in the world but it works pretty good for me. I want to extend my focal length but i don't have the money for a new lens. I've been looking at teleconverters and it seems like it would be the most cost efficient for my needs. I'm not sure what i should go with. I've been looking at some tamron autofocus teleconverters and they seem pretty cheap but also have decent reviews. I was thinking of going with a 2x but i'm not sure. would there be any negative effects? I know i'm going to lose i think one full stop of light or more, but if it's overcast or low light conditions i won't be using the lens/teleconverter any way. I'm starting to get more and more serious about photography it's now become my major. Ultimately i'd love to have the ef 70-200mm f/4L usm lens with a teleconverter. But i'd also like to be able to have a longer reach on my photos immediately and the 70-200mm f/4L is out of the question at the moment. does anyone have any suggestions or more information on teleconverters that could help me make this decision?