Question

Why are f1 2 lenses so expensive?

Answer 1

An f/1.2 lens had much more glass than say an f/2.8, e.g. a 50mm f/2.8 lens would have an effective aperture of 25mm, while an f/1.2 50mm would have one of 41.7mm. This means the optical elements had to be much larger for an f/1.2 lens.