Wide-Open,
Wide-Open by
fiftyonepointsix, on Flickr
This is a classic Planar 1-2-2-1 6-element in 4-group lens, the formulation made possible with a high-index of refraction/ low-dispersion glass pioneered by Canon. Unfortunately - that type of glass often reacts badly to oil outgassing onto the surface behind the aperture blades. This one is perfect, some were lucky. Be sure to have inspection and return privilege for this lens when buying.
The Canon 50/1.4 uses 48mm filters, like many Canon cameras and lenses of the 1950s through to the early 1980s. Not a common size, but not too hard to find on Ebay.