Joseph Moniz , Jun 28, 2000; 06:05 p.m.
A macro extender, or extension tube, will allow a lens to focus closer. You will sacrifice infinity focus to do so.
A Teleconverter/teleextender will increase the focal length of your lens, but (usually) wlll NOT allow your lens to focus closer.
Both items will cause a loss in light transmission to your film. If you do not have TTL metering you will have to experiment to find the correct compensation to adjust for this loss of light.