When I half-press the shutter button on the E-PL1, I notice the aperture on the lens (in this case, Lumix 20mm 1.7) opens up wider and the image displayed on live-view will brighten. At the end of the focus cycle, the aperture gets smaller and the picture darkens. I am using Aperture mode and setting the f-stop to 1.7. This post explained the reason for this is that the f-stop used for the E-PL1 live view is 2.8. When focusing, the aperture opens up all the way before coming back to 2.8, then supposedly opens to the selected aperture size for exposure. But, I am noticing that none of my pictures appear as bright as when the picture on the live view brightens from the aperture opening all the way. If the brighter picture on the live-view during the focus cycle is a result of the aperture temporarily opening all the way, why isn't my picture as bright as the live-view if I am setting the aperture to 1.7 for the actual exposure?