I always assumed that there was a fixed relation between focal length and angle of view. But compare the technical data for the following lenses, all from the same manufacturer:
- Canon EF-S 15-85mm f/3.5-5.6 IS USM -- horizontal field of view (at 15 mm): 74°
- Canon EF 24mm f/1.4L II USM -- horizontal field of view: 74°
Why do two lenses by the same manufacturer have the same angle of view at different focal lengths?