Seagull

Seagull -- 1D IIn & EF 200mm f1.8L @ f2. Click to see larger.

When I bought the Canon 100-400mm lens, I had the intention of shooting birds/wild life with it.  But, as it usually is the case, I just couldn't find the time/opportunity to use it much.  Consequently, the lens was very infrequently used, and finally traded for a more useful 16-35mm lens.  The 200mm f1.8 (and the 70-200mm f2.8 IS) becomes the longest auto focus lens I now have.  With a 1.4x/2x Canon teleconverter, I don't think I am losing much in terms of optical quality/reach.  Strangely enough, even though I have the the 1.4x (and the 2x) converter for years, only the 1.4x was used once with the 100-400mm lens.  I have never tried them with the 200mm f1.8L.  I know the focusing speed will be slower with the converter, but optical quality should be quite good.  Perhaps it's time to give it a try.