This article is the third in a series teaching the basics of
photography. We started by learning about the properties of
light and how an image is created, and we also learned how a
lens bends light to focus individual rays into a single bright
image. With this lesson we are going to finish learning the
scientific theory of lenses and how to use lenses for
magnification in addition to brightness. In the last lesson we
performed an experiment to focus the light of a candle through a
lens. We also learned that to determine the focal length of the
system, we move the focusing screen forward and backward until
the image of the flame is in focus. Let’s consider that
candle/lens system for a moment. What do you think would happen
if we replaced the lens with one that is twice the diameter with
the same focal length? Would the image be twice as bright? Image
twice as large? If you guessed the larger lens would make the
image brighter, you would be correct. The larger lens has more
area to collect light, which actual