Having a Canon EF 70-200 F/2.8L USM IS len only gave me the quality but not the range long enough for wildlife shooting, so I bought a Canon 2x Teleconverter to allow me to reach 400mm range. As the focal length is doubled, the maximum aperture is cut half, the len is slower. With the teleconverter, the F/2.8L len becomes F/5.6L, but IS (Image Stabilizer) feature still functions normally. The image quality is generally retained when working with the Canon L serial lenes. I can see the image is not as sharp as without the teleconverter, but I don’t notice any distortions in the pictures.
Now, the 70-200 F/2.8 USM IS len, the 2x teleconverter plus my camera body (Canon EOS 10D) weights 6.7 lb. My photo bag (LowePro Flipside 400 AW) with all the gears is more than 14 lb. The next two pictures are to compare the 70-200 F/2.8 USM IS len working with (up) and without (bottom) the 2x teleconverter. Some snapshots are followed.