I am not a UFO guy, but... I shot over 2400 images in four hours during the Saturday air show. These two images - the only two - contain an odd saucer shaped artifact that is pointed out with the arrow. The subsequent frames I was shooting of this biplane - at 9 FPS with my D3 - do not have the artifact in them. Very strange indeed. It was over NASA's Shuttle Launch Facility so...

If anyone has a clue what this thing is, please share.