I don't have any personal experience with that particular teleconverter, but
if it exhibits the same optical qualities as the other ones I've used, I
would predict that you will notice a significant degree of loss of
resolution and possibly less-saturated colors.

Whether the resulting image quality is something that is tolerable is a
decision only you can make.  I have been unimpressed with teleconverters,
and even when I was able to get shots that I would otherwise have missed,
the reduced quality of the images were such that I almost wished that I
hadn't bothered at all.  You may not be as critical, so don't accept my word
on how the images will turn out.

You also have to deal with the exposure factor.  Teleconverters require
additional aperture openings in order to compensate for the reduced light
reaching the lens (or you can slow down your shutter speed).  That may
result in softer images or camera shake.

A teleconverter should be thought of as more of a band-aid approach than as
the equivalent of a longer lens.  As with everything in photography, the
increased focal length comes at a price.  If you regularly require the
increased focal length you will probably be happier by getting a real
telephoto lens.  Sorry if I seem pessimistic, but I have not found the
advertising hype for teleconverters to be accurate.  I rarely use any of
mine--perhaps a couple of times per year.  If they became lost or stolen, I
wouldn't shed a tear over them.

It's very good indeed. I've shot professional purpose stock shots using
it, and found the sharpness completely unimpaired. But it needs special
attention to supporting the lens when extended to 200mm to use the
converter, and you literally have to cradle the lens/converter assembly
ALL the time in your left hand and NEVER let go.

David

If that's the ACT-100, then yes, it's a lovely piece of glass, much
better than 'typical' add-on teleconverters.  Only 1.5x though..

But it weighs a ton and is huge - you should hold one before you
consider it.  As mentioned by another poster, it must be supported -
you'll understand when you pick it up...

Others have answered.
What I would suggest here is besides the ACT-100 from Minolta, try to
find
som TC from, say Olympus, like tcon-14, tcon-17, or the old A-200. All
should
be have for a better price.
Hope this helps.

Pinwu

Thanks to everyone for setting me straight about hot pixels and the causes
of what I thought were anomalies.

Toby