Originally Posted by Spavinaw
Just a bit of trivia: The metal rim of my Canon orange 58mm filter is engraved as follows, "CANON LENS 85mm f:1.5". However, it is not a lens (no power}, it is not 85mm, and it is not f:1.5. At least it is Canon. As you've heard before: Don't believe everything you read. This includes GPS navigation systems.
This filter was part of a set made for the Canon 85mm f/1.5 LTM lens which has a 58mm thread. They were available as single filters with bakelite case or as a stacked set with the corresponding colors like the 50mm f/1.2 LTM set shown above.
As far as I know, the 50mm f/1.2 and the 85mm f/1.5 were the only two lenses that Canon had filters specially marked for them. The same filters were of course available as generic 55mm and 58mm variants.
None of the 40mm filters were marked specifically for any lenses.