You point your camera to take two random shots (say a lake scenery at a state park). You are shooting at aperture priority mode (say f/9.0) your ISO is set to 100 and camera uses 1/250 to obtain the correct exposure. For the first shot you use wide angle end of the lens(something like 18mm) and 50mm for the second shot. Since all the settings, camera angle and location are same for both shots, and you use the same lens (say f/2.8 throughout the zoom range) you would expect the camera to use the same shutter speed for both shots. But it doesn't. I did this test a few times outdoor today and camera shutter speed changes as I zoom in and out. The change is not a drastic change but it changes. And I cannot explain why. Could someone?