Besides the macro aspect is there a big difference between the Sigma 28-70mm f/2.8 and the Sigma 24-70mm f/2.8 lenses? Is the 24mm worth the extra $60 on a Canon Xt? Currently I am using the Sigma 17-70mm but would like to have the f2.8 all the way through. I would use the lenses in question mainly for indoor shooting. I am not to concerned about the macro aspect at all as I use my Sigma 70-300 lens for that. Thanks!