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This article discusses the feasibility of using the Canon EF 1.4x II
teleconverter on Canon lenses that are listed as being
non-compatible with it. Canon states that the 1.4x and 2x
teleconverters will not work
on any prime lens under 135mm nor any zoom lens with a lower focal
length less than 70mm such as the 28-300mm L. Why not?
Physics dictates that it should work since everything is in
the
same plane. A lot of sites state that it is an issue
with auto-focus or metering, but with manual focus and ETTL, this
should
be a non-issue, right? Not exactly, before you try
to mount
any of the teleconverters on a lens that is stated as being
incompatible read on.
The real issue with using these lenses with the teleconvertes from
Canon, is that the rear element of the lens sits almost flush with the
lens
mount or in some cases slightly protrude beyond it. In the case of the
85mm, this makes installation of the
teleconverter impossible. You can get around this with extension tubes,
but your focus will be effected and you will lose the ability to focus
to infinity. The same issue is present on the 28-300mm L zoom, but for
this
there is a work around.
Because
the Canon
28-300mm L IS USM is
a zoom lens, the only time the rear element is all the way
back,
is at the lower
range of the focal lengths. If you can limit this range, the lens will
physically work with the teleconverters. I have read about using
everything from moving the tripod mount forward, to wrapping the barrel
with tape, to limit this range. The best
solution I found, came from a discussion on Flickr and
suggested
the
use of the popular wrist cancer bands endorsed by Lance Armstrong. They
are inexpensive, robust and resist the elements well. Their pliable
polymeric construction also will not mar your lens' finish.
In addition, purchasing them benefits a great charitable cause.
Different charitable causes have different colored bands. In
the
case of the 1.4 teleconverter you will need to install two bands. The
addition of the two bands will effectively limit your lens from
resolving below the 60mm focal range when the teleconverter is not
mounted and will also limit the travel of the rear element and keep it
from coming into contact with the teleconverter. Upon
mounting
the Canon EF 1.4x II telecoverter, it will effectively become an
84-420mm f8.0 zoom.
Above you
can see the
Canon EF 1.4x II teleconverter mounted to the Canon 28-300mm L IS USM
1:5.6 lens with bands. In this configuration the lens
will have full function on all professional EOS 1 series camera bodies.
Metering will correctly work on all other EOS
consumer
bodies, such as the Canon 10-50d, but
they will not have the auto-focus capability, because adding the
teleconverter increases the minimum aperture from f5.6 to. f8.0.
EOS consumer bodies will not auto-focus on Canon lenses with
minimum apertures above f5.6.
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