Purpose:Use the three principal rays to locate the virtual image of a diverging lens.
Description:The central ray passing through the half-silvered mirror serves as the optic axis. The vertical ray between the two mirrors serves as the object arrow. By rotating the mirror at the tip of the arrow, the three principal rays (or any desired ray) can be produced. The tip of the image is located at the point from which the three principal rays appear to diverge, which can be determined using a meter stick and marking the point with black tape. The focal length of the lens is about -34". Two lenses may be hung back-to-back to shorten the focal length to about -17", which increases the divergence and may aid in viewing ease but at the expense of image size. The single convex lens before the object helps to keep the light ray narrow. Do not use the extreme edges of the lens to avoid serious spherical aberration.