1.4x Closer and Still Sharp

The Tamron 1.4x tele-converter will change your 200mm lense into a 280mm with a minimal loss of sharpness. Doing a Google search for this converter you can find many articles that compare the Canon, Sigma, and Tamron 1.4x converters and it appears to me that the consensus is that they all give very similar results.

The Tamron and Sigma converters have two advantages over the Canon though, they are less expensive and they will work with many more lenses than the Canon converter. The Canon converter can only be used with a select few telephoto lenses.

Keep in mind that using any teleconverter will slow your lens down, the 1.4x will make a f/2.8 lens an f/4 lens, and will decrease the sharpness of the pictures taken.