Help! I own a 450D/ Rebel XSi. Today (May 16, 2009) I bought a EF-S 55-250mm f 4-5.6 lens. This is not an internal focusing lens (front of the lens rotates while focusing). My interest is portrait photography and this lens covers two traditional portrait focal lengths 65mm (105 mm equivalent) and 83mm (135mm equivalent). But I found out that if a leave the lens at any focal length (55, 70, 100, 135, 200, 250 etc) and than focus (manually or auto), the perspective/ angle of coverage changes. That is, for a same subject at a same distance using a same focal length, the closer the distance I focus, the viewfinder (and final image) shows a tighter angle which means the focal length increases. The focal length ring does not rotate while it happens. Why is it happening? Is it normal? Does anyone have any experience regarding this? As far as I know, it may happen to internal focusing lens. But why is it happening with this lens?