On Tue, Jun 05, 2007 at 10:30:12PM -0500, Roger Eichhorn ([EMAIL PROTECTED]) 
wrote:

> It appears that the extenders only work with L series lenses.  Is  
> this correct,

Almost, but not quite.
Canon's extenders indeed only work with a limited set of lenses,
but that doesn't include all L series lenses yet includes some
non-L ones. They also work with various non-Canon lenses
(no way of being sure which ones without trying).

Some 3rd party extenders don't have such limitations and
work with all lenses, and only those can be used with
any of the 7x-300 lenses. They're cheaper, too, but
(unsurprisingly) of poorer optical quality as well.

> and if so, what happens if one tries to use them with  
> non-L lenses?

They don't physically fit. The TCs extend physically into
the lens, so they only work with lenses that have enough
space there.
With some zooms it is possible to use the TC when zoomed
out, but zooming in will cause the usually unwanted sound 
of two pieces of expensive glass hitting each other. :-)

It is also possible to use TCs with more or less all
lenses with an extension tube, losing infinity focus.
That makes sense mainly with macro applications:
the 100/2.8 USM macro + 25mm extension + 1.4x TC
works quite well, for example. 

-- 
Tapani Tarvainen
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