An 18-200 kit lens is too slow for weddings…maybe for outdoors but indoors the minimum would be f2.8 for better picture quality and that is with a max 800 ISO. If you want a zoom lens then use the Canon 70-200mm 2.8 or the Sigma 70-200mm 2.8. For darker receptions we use lenses in the 1.4 to 1.8 aperture range.
