Kenko Teleplus MC 1.4 PRO 300 DG, Canon

Kenko PRO 300 3.0x                     
Placed between the camera body and lens, a teleconverter contains a set
of optics that will effectively increase the focal length of a lens by
a specific amount. Common magnifications are 1.4 times and 2 times, but
the Kenko Teleplus PRO 300 AF converter has a 3x magnification. For
example, using a 3 times (3x) teleconverter will increase the focal of
300mm lens to 900mm.                       
The Teleplus PRO 300 converter is made with high quality multicoated
optical glass supplied by Hoya Corporation, the worlds largest
manufacturer of optical glass. The PRO 300 3x is designed for use with
lenses of 50mm or above and work best with telephoto lenses of 100mm to
500mm. The PRO 300 3.0x can be used with telephoto zoom lenses as well
as prime lenses. However, Kenko does not recommend them for lenses that
have a zoom range that starts under 50 mm.                      
KENKO PRO 300 AF Teleplus converters have genuine Gate Array IC
(Integrated Circuitry). It means that the converter’s unique circuitry
maintainS signal integrity between the camera body and lens. These
converters are designed to electronically operate the same way an
original manufacturer’s converter would provided there is enough light
available.                      
Important Note: Due to the 3 stop light loss inherent in a 3x
converter, Kenko states that the PRO 300 3.0x converter will not auto
focus with lenses that have a smaller aperture than f/2.8. With all
lenses having apertures smaller than f/2.8, Kenko recommends using the
PRO 300 3x in manual focus mode.         
Kenko PRO 300 2.0x and 1.4x

KENKO Teleplus Pro 300 converters are made with precision quality
multicoated optical glass supplied by Hoya Corporation, the worlds
largest manufacturer of optical glass. These glass elements were
designed to match the optical quality of the prime lens (even at the
edges) and telephoto zoom lenses. The optical design of the elements
and light path is wide enough not to cause vignetting.                       
The PRO 300 family are designed specifically to be used with prime
telephoto lenses of 100mm or above, such as the Tokina AT-X 300 AF PRO,
300 mm f/2.8 lens, and work best with telephoto lenses of 200mm to
500mm. The PRO 300 can be used with telephoto zoom lenses as well as
prime lenses. However, Kenko does not recommend them for zoom lenses
that have a range starting under 50 mm.                      
KENKO PRO 300 AF Teleplus converters have genuine Gate Array IC
(Integrated Circuitry). It means that the converter’s own unique
circuitry maintains signal integrity between the camera body and lens.
These converters are designed to electronically operate the same way as
an original manufacturer’s converter.1                      
Full AF operation with PRO 300 2.0x is possible when using camera
lenses with maximum aperture of F2.8 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
required when using lenses with smaller maximum f-stop value than those
given above.)                      
With the PRO 300 1.4x, full AF operation is possible with camera lenses
having a maximum aperture of F4 or brighter. The same light and
contrast requirements apply.                   
1.
Most Canon EOS camera bodies are programmed to shut down auto focus if
the calculated effective aperture for the lens and teleconverter is
smaller than f/5.6, the Kenko Teleplus PRO 300 converters work the same
way.