Over the years since inventing 35mm photography, Leica have produced some interesting sometimes limited edition lens. An odd one is the M glass 66mm. Olympus liked their 55mm, and Nikon had a classic 58mm. Leica’s 66mm is an interesting choice of focal length, an in-between choice similar to the 40mm that has become popular recently.
Not sure how many Leica made but most of the uk stockists are sold out.
I am intending to add a 40mm to my collection at some point. Any none standard focal lengths you like?