Making things look bigger
When you use an optical instrument, whether
it be something very simple like a magnifying glass, or more complicated
like a telescope or microscope, you're usually trying to make things look
bigger so you can more easily see fine details. One thing to remember
about this is that if you want to make things look bigger, you're always
going to use converging mirrors or lenses. Diverging mirrors or lenses
always give smaller images.
When using a converging lens, it's helpful
to remember these rules of thumb. If the object is very far away, the
image will be tiny and very close to the focal point. As the object moves
towards the lens, the image moves out from the focal point, growing as it
does so. The object and image are exactly the same size when the object is
at 2F, twice the focal distance from the lens. Moving the object from 2F
towards F, the image keeps moving out away from the lens, and growing,
until it goes to infinity when the object is at F, the focal point. Moving
the object still closer to the lens, the image steadily comes in towards
the lens from minus infinity, and gets smaller the closer the object is to
the lens.
Note that similar rules of thumb apply for
a converging mirror, too. |