When my 55-62mm step-up ring arrived in the mail, I very proudly let my wife know how much money I had saved over the alternative of buying a 55mm polarizer. When she asked me what the difference is between a 55-62mm step-up ring and a 62-55mm step-down ring, my pride and no doubt the smile on my face immediately vanished. That's because I had no idea (and still do not).
What's the difference?