Obviously canon has a big name so therefore bigger price. But they are also quality. If I were to find a similar lens but by Sigma, would I be getting lesser quality? I dont want to sacrifice quality by going to a less expensive, identical lens from Sigma. I want to know if there are any similar lens compared to EF 70-200mm f/4L USM and what their prices are. Also is Sigma is cheaper, how much are the F/2.8 and IS versions? Whatever "IS" is called for sigma hehe. Thanks!