In the endless search for more Zoom, I bought this 2X Converter off ebay. I couldn't find any reviews of it - I think it's pretty old - and you take a big chance with cheap converter lenses, but at £6.50 I thought I'd give it a chance.
Here's the test result. We've already established that at high zoom, the cheaper Panasonic SDR-S26 does a better job than the expensive SD900. Does adding the converter to the SD900 makes it better than the S26?
I think so, but there's not a lot in it. More testing required!