Lots of interesting information in this link... In general, zoom lenses are a compromise from primes. But this generality in no way means that ALL zoom lenses are worse than ALL primes. Or that there are not excellent zooms, and poor primes. Canon is very good about providing MTF "sharpness" data on all of their lenses (on Canon website). I also had a link to a 3rd party lab which publishes MTF data from many lenses. Right at the moment this link is lost somewhere in my computer, but some google searching should locate the site. I really like my Sigma 20mm. Can't say really if I'd like the Canon more or less. There are some test sharpness shots hiding somewhere here in the Forum. Search for "Lens Test," should turn up something.