I shoot a Canon EOS 7D. As well as some Canon lenses, I also own some Sigma lenses. I acquired an ƒ/2.8 70–200mm Sigma a little while ago.
Now, something about using Sigma lenses on Canon bodies bugs me. See if you can spot it in this screenshot from Aperture (bear in mind the image was shot using the 70–200mm):
See the lens model at the bottom? It seems the Canon “brain” sees the Sigma lens, but identifies it as an ƒ/2.8 50–150mm plus a 1.4x extender! Do the maths, and you’ll see this odd combination actually works out as a 70–210mm. It’s not just this lens, either. All my Sigma lenses, both EF and EF-S compatible, are reported incorrectly in the EXIF from the camera. Weird but true.
It would be really nice if there was a way to correct this, either in the camera or within Aperture. I haven’t found a way yet.