>If I drive the internal focusing elements of the TC-16A to one end (the >front end?), will the AF 300/2.8 focus closer than it would without the >TC-16A? You would imagine that the TC-16A forms a (very short) >extension tube. >From my experience with the 16A and 300mm f/4, the decrease in the near focus distance is so small that it has absolutely no practical value.