In case anyone is interested I bought a Canon lens recently and was intrigued to read that although it was compatible, "Sales of the 500 Close-up Lens may already be terminated in some areas". The 500D appears to be fully available though (try getting one - they are often out of stock!).
Despite being a single element design, this may be a useful lens for underwater photographers as its available in 72mm and 77mm fittings and is a good quality optic at not too high a price and may well be a good diopter to use behind a dome port (I have others that I use so I haven't tried it myself). So it looks as though if you want one it looks as though it should be bought in the not too distant future as it appears to be going out of production reading between the lines.
