I've noticed several times now, that my images are very easily overexposed when I'm using the Tokina 10-17 at 10mm. Even with low iso (100), a fast shutter speed (1/320) and small aperture (f22), images are often over exposed, especially with sunburst close to the surface. But when zooming in just a little bit, like 10.5 or 11.0 mm the exposure (with the same settings) is completely different: almost completely dark! Is this expected? I understand that due to the wider angle of view, more light is captured, but I didn't anticpated such a drastic change. Do I miss something?