There are a couple choices. The "best" in my own experience is the Olympus TCON-14B which is a 1.45x adapter which will give you pretty good zoomback range and a maximum of 626.4mm focal length. Chromatic aberration is minimal and the lens is extremely good from an optics perspective having been designed for the Olympus E10/E20 cameras.
The 14B (not to be confused with the TCON-14) is a large, heavy lens which must be supported with one hand when attached. You will also need an adapter "tube" which is available from a couple places.
The other choice is the Olympus TCON-17 which is also quite a good lens, but not quite as "sharp" as the 14B. The TCON-17 is a reincarnation of the old Olympus B-300 which was used on some Olympus fixed lens 35mm film cameras and worked quite well for a wide variety of fixed lens digicams. This one is 1.7x and gives you a maximum of 734mm but with less zoom range available than the 14B.
I have both these and use them with a variety of my digicams incluing the FZ10 and FZ20. Of the two the 14B is, in my opinion, the better way to go. It's larger and heavier then the 17, but has better optical properties.
Lin
