Cosina/ Voigtlander 50/1.5 Nokton Aspheric, LTM
This is a great lens, and will soon be re-introduced in M-Mount. I like the LTM version, wide-focus ring and a more modern design. This is a big lens, and uses 52mm screw in filters- the same as the 35/1.2. Also the same as Nikon has used for decades.
All shots wide-open at F1.5, on the M Monochrom with a single-coated Nikkor O56 Orange Filter.