Why do we have in a camera a lens(镜头)instead of a simple hole?

　　The reason can be seen from the figures(图像).

　　In Figure 1, the hole is small. Rays of light from a point (P1)outside reach a very small part of the wall opposite, and we see there a small point. But when the hole is bigger, as in Figure 2, rays from the point(P2)can cover a larger part of the wall opposite, and we don’t see a clear point, Rays from other points(Q) outside can also fall on the same place inside. Therefore the picture is not clear when the hole is big and it is not bright when the hole is small because very very little light can pass through it.. We can get better result with a lens. If the lens is made in the shape shown in Figure 3, all the rays of light from the point(P3) are thrown on point(P’) inside. The picture which we see, therefore, is clear, and it is also bright because more light can pass through a lens than through a small hole.

为什么我们在相机镜头(镜头)而不是一个简单的孔?

　　原因可以从图表中看出(图像)。

　　在图1中，孔小。从某一角度的光线(P1)在到达对面的墙上很小的一部分，我们看到有一个小的点。但当孔比较大，如图2，从点线(P2)可以覆盖更大的相对的壁部分，我们没有看到一个清晰的点，其他点的射线(Q)外还可以落在同一个地方。因此，图像不清晰时，孔大而不亮时孔小，很小很小的光可以穿过它。我们可以用一个镜头得到更好的结果。如果镜头是在图3中所示的形状，所有的光线从点(P3)抛出点(P’)内。图中我们看到，因此，是明确的，也是因为更明亮的光可以通过镜头比通过一个小孔。