Hi, I am new owner of a Canon XSI, and new to digital SLRs. I purchased the XSI from costco-it came as a kit w/a 18-55mm and 55-250mm lenses. I'e played around with the kit lenses, and have started buying other lenses-better lenses. So far I have in my hands is a canon 10-22mm, and am waiting for my 70-200mm f/4Lnon IS to arrive. I am looking for a good walk around to add to my arsenal. I am a volunteer firefighter, so I need a lense on my camera for a quick shot when we first arrive to something exciting, that can capture just about anything in various lighting conditions. Since I am covered on the wide side, and the zoom side-can anyone help me on the middle??? I have read about both of these lenses...but I am torn as to which to choose from. I do like the L lense on the 24-70...help...Cathy