I'm using the extender in conjunction with the following lenses: EF70-200mm 2.8 L IS II USM, 2.8 L IS USM and EF300mm the EF400mm 4DO IS USM and the EOS 7D. Although the focus is running slower, I have managed to take birds in flight. Only at 400 is only manual focus is possible. Since the lenses are already delivering superior image quality and the Extender to no image loss results, it has doubled the focal length cost. On technical details I will not go into that have already done a number in front of me. I value what I see. The two Aperture which swallows the Extender, are irrelevant, since I usually receiving the "Action" with Aperture 5.6 or later. Even PC I am of the detail of zBFederstrukturen amazed at what surprised me, because it is generally the Extender result in a loss of image. That may be true in the case of measurable and non-manufacturers also. Since I only Scan system compatible with Canon products, I have not had any negative experiences. The manual focusing on 400's unless a problem, at a 800-focal length because I slower anyway objects Scan. Since I also use the 1.4 Extender, here was also noted: The focus is insignificant and slow also no loss of image quality. (Slow at an extremely high level!)
Conclusion: A premium product which has its price. The result stands out, especially when the third party results . see
Strong buy recommendation!
Addendum: I recently tested the Extender with my 300er fixed focal length again. The resulting focal length 600mm 5.6 aperture has a legendary quality. To get the most out of this lens, I also focus manually. Earnings hit me on the computer in the appropriate magnification smooth the stool. Details that were not visible are clearly came to light. Negative reviews on this Extender I can not understand at all.
