Diamond has a very large index of refraction and therefore a small critical angle of only 25°. If the diamond is cut correctly light striking the top of the diamond will be internally reflected and will emerge again from the top rather than the sides of the diamond

The diagram below shows what would happen if there were three pinholes, each creating an inverted reproduction of the object (see page 211).

Now, if a converging lens is placed just behind the pinholes it will bend the rays going through it. If the focal length of the lens and the distance between the lens and screen are chosen correctly, then the three reproductions from the pinholes will all be at the same location. Light rays from the top of the object will converge on the appropriate point on the image. Note that the image is inverted and the same size as the reproductions. What would happen if you had a multitude of pinholes at the location of the lens? The reproductions from all the pinholes would be at the same location, and many more rays from the object would end up at the same place on the image. The image would be much brighter. So, you can model the formation of an image by a lens as a collection of reproductions of pinholes. The larger the lens, the brighter the image.