Summary: This 1.4 teleconverter works great with my tamron 70-300 f5.6. Focus is quick with my Nikon D7100 and the image quality is excellent. It is not going to match a 400mm prime but for what I have invested, I have no complaints.
Sharp, but does *NOT* AF on Sigma 300-800mm f/5.6 for EOS
Steven Young, Amazon
11 June 2014
Summary: I already have a Canon 1.4x TC II which is fabulous, sharp and quick on the AF but it would not work with my Sigma 300-800mm f/5.6 super tele, even with my 1DmkIV which should allow autofocus up to f/8, unless I taped the pins. That's less than ideal because it fools the camera into thinking that there is no TC attached and so the AF kind of "bounces" a bit before it locks on. It also doesn't report EXIF info properly.
Summary: I have used it on various Canon lenses for still pictures. As of now, I have not used it for action shots. It cannot be installed on my Canon 18/200mm Lense. This teleconverter cannot be installed on any lense that has a white alignment marker. It works with lenses having a red marker.
Summary: It works as advertised and the reviews are quite correct. The results are nearly perfect, especially if you are willing to live with a little extra softness and some chromatic aberration. I used it with my cheaper 70-300 and was disappointed. Once I switched to a Nikor lens, the results were more to my liking. I did not want to spend the big bucks for the extra reach and this is a compromise I can live with.
Summary: Works great with Nikon D5300 and 18-300 Nikor lens. Remains sharp a full zoom and the AF and metering worked throughout the entire range. Little tricky with low light shots but hey you loose one complete F stop and save about $5900 bucks if would have purchased a Nikor telephoto lens.
Summary: This has worked very well for me shooting macro. I'm very satisfied so far. I have not had a chance to use it on my 70-300 lens as of yet. It's costs far less than the Canon model and I may even buy another one.