Bill Crocker wrote:
As a rule, extenders do a lot to degrade the image. Added to that, Tamron
leaves a lot to be desired. There is a reason why Canon's cost more.
Consider using a Canon 1.4x, if you have to use one at all. A 3x is almost
a joke.

This is incorrect. While an extender magnifies the image of a lens,
and therefore any defects in the image, a good sharp lens
will do well with a good sharp extender. Here are some lens tests
with and without extenders (kenko pro 300 extenders):
http://clarkvision.com/imagedetail/r...lens-sharpness

I use Kenko pro 300 extenders and they are very good. I even stack
the 1.4 + 2x on a 500mm f/4 IS L lens and get excellent
results and still get autofocus with a Canon 1D Mark II.
Check these Alaskan brown bear images, each with
technical details to show what was used:
http://www.clarkvision.com/galleries/gallery.bear

You can also check my bird gallery for other examples.

The 400 f/5.6 L is a sharp lens, and will deliver good images
with extenders if you can manual focus. Get the
"right angle finder C" as it magnifies the image and will
help you manually focus. Also, get a good extender.

Roger


"Don" wrote in message
...

Folks

I have been trying to use the Tamron SP AF TeleConvertor 300F-CA 2X with
my 400 F5.6 L series lens but the results are dismal. I obviously was
aware I would have to manual focus but I haven't been able to get a sharp
shot or even a keeper for that matter yet. Any one has any ideas or
similar experience or would care to comment and assist me if I am doing
something wrong. I have tried from F11 to F14 on tripod etc.

regards

--
Don From Down Under