What is a "professional" lens?

[Photo-John]

There are three things that make a lens a "pro" lens. I mean, three things besides the price

1) Fast, fixed aperture - usually f/2.8 or f/4. But depending on the lens it might be even faster.

2) Build quality. Pro lenses are built for abuse and usually have internal focus and zoom mechanisms.

3) Better glass. Better glass means sharper photos at all apertures, better color and contrast, and less flare.

Most people can tell the difference in image quality between a consumer lens and a pro lens. For instance, take a look at reviews for Canon L lenses and you'll find lots of reviews where people say they were skeptics until after they bought, borrowed, or rented an L lens. Better lenses really do make a difference. A better camera usually doesn't make that much difference unless you're shooting sports or some kind of technical photography that really benefits from speed.

[walterick]

I agree with Greg and John. The only thing I might add is they usually have the lens distortions controlled better as well.

Rick