Aperture 2 can extract metadata about the lens model you used from your image’s EXIF, if your camera writes it. A few little points I discovered about this:

Firstly, the field is not shown by default in the Metadata panel. You have to go to the Metadata tab, disclose the EXIF panel at the bottom and then select the checkbox beside the Lens Model field.

Sweet. I loves me some metadata. Now to make it play nice with my website. You see, mere focal length isn't enough.