A couple of sites have announced the new Elpro 52 - an accessory lens for turning "select" M and TL lenses into Macro lenses. The 52 is for the 52mm thread, which does not exist on any M lenses. However, the Elpro comes with a 46mm and 49mm stepper, so that you can use it on some M Lenses (like the Summicron 75mm). But for other filter thread sizes (like the 39mm on the Summicron 35), you will need a third part step down adaptor. After some searching, I did find a page with links to downloadable PDFs: here. To save you some trouble, here is the PDF file converted to JPEGs.