Purpose:Encourage thought regarding how an image is formed.
Description:An arrow/circle cross object is imaged on a screen by a 150mm focal length convex lens, as seen in the center photograph above. The experimental setup is shown below, with the object at the left, the lens in the center, and the image screen at the right in the photograph. A paper baffle is then stuck onto the lens, as seen in the photographs below, blocking half of the light passing through the lens. What happens to the image? Encourage your students to make a prediction. Will it remain unchanged; will it become brighter; will it become fainter; will the left side be gone, or will the right side be gone? Shown also are the image without the baffle on the focusing lens and with the baffle on the focusing lens. The image with the baffle in place is clearly fainter than the original image, as can be seen.