.miles

There is a well known twilight image of a lion taken by Frans Lanting that exhibits eye shine.

For my nocturnal wildlife images I do not bother to remove the eye shine as I cannot make

the image without flash and as such, the light for the image is entirely alien to the scene.

Autofocus systems need contrast to work properly, if there is not enough light your lens will

hunt for contrast. Manually focussing the lens is the easiest way to make the image in these

conditions. There are other ways to add contrast to a scene though.........

Add me to the list of the surprised.

Your test still leaves some questions without answers. Did you get a bad example of the

Canon, did you get a great example of the Tamron? The test can't tell us the variance that

exists within examples of these teleconverters.

You did what I would have done though, you kept the better and less expensive tool.