The Tamron SP AF Pro teleconverter features improved optical
construction, and is designed to be used with lenses that are f/2.8 and
of focal lengths of 90mm or greater.
The 2x teleconverter (also known as a tele-extender) will multiply
the focal length of the existing lens by 2x, and will cut back the
amount of light by 2 f/stops. For example, using a 2x teleconverter with
a 300mm lens will effectively increase the focal length to 600mm. A
lens set to f/2.8 will now be f/5.6.
This teleconverter is not
recommended for lenses wider than 90mm, e.g. 50mm, 28-105mm, etc.
However, full AF operation is still only possible with lenses with open
aperture of f/2.8 or brighter. Please be aware that AF will work
properly only if there is enough light and contrast on the subject to
activate the camera's AF sensors. Manual focusing is recommended when
using lenses with smaller open f-stop value than those given above. This
teleconverter is compatible with the EF lens mount only--not compatible
with EF-S lenses.
When used with lenses with smaller maximum apertures (f/4 and f/5.6,
for example), there will be little difference in image quality as
compared with the standard Tamron teleconverters. When used with lenses
wider than 90mm, the SP teleconverters can actually compromise image