I have a canon eos 5 & 500 and have been looking at the cosina 19-35mm. I have a 28mm and am not sure how much difference would be visable between the two. Also is the quality of the lens in question any good? It is fairly cheap (£160) bu as I only occaisonly do landscapes would it surfice? I also wish to purchase a Jessops 2x teleconverter that I would use on a 300mm sigma lens. Will I loose much in terms of picture quality? Thanks for any advice, mario.