I picked up a "Vivitar Macro Focussing 2x Teleconverter"
Does anyone have any comments on them?
Are these only for macro use or can you use them on tele lenses?
I've got one that I use on my Olympus cameras. I haven't used it for distance work but I find it to be a good quality and very flexible aid for close focus work.
FWIW, I don't own any macro lenses for Olympus.
Here is a link to an interesting discussion on another forum:
It's a doubler. So you use it with any lens you can mount to the camera. One note, as it doubles focal length it also reduces any aperture by one stop; 4 becomes 5.6, 11 becomes 16. Have fun with it.
It's a high quality 70 elemnet 2x macro focusingh teleconverter. Works best with primes. There is also a similar non-macro 7 elemen teleconverter made by Kiron (Kino Precision Instuments). Both are very good and made by Kiron.
The Vivitar is a good 7 element 2X teleconver. It is basically the same as the Kenko. When Hanimex bought out Vivitar in the early 80's they sold the rights for the 90mm f2.5 S1 macro and the 2x macro teleconverter to Tokina who introduced their copy of the macro lens under their own name, and the 2X macro teleconverter under the Kenko brand.
The manual can be found at http://olympus.dementia.org/manuals/Vivitar-MFTC.pdf