Activity 12

We use lenses everyday whether we know it or not. There are two lenses in each of our eyes: the cornea and the crystalline lens which focus light onto our corneas. Lenses are used to not only correct our vision, but to enhance it by letting us see worlds we normally wouldn't be able to see, via microscopes and telescopes.

Optical Images

Go to the Images of Nature website <http://ion.asu.edu> and see the collection of images listed in the Index. You can download any of these images for your own use.

Magnification and focal length

A simple microscope

a) Put a drop of water on the clear sheet to form a water lens 5 millimeters (mm) or greater in diameter. Use a bright lamp (desk lamp) as a light source and hold it over a paper so you can estimate the focal length with a ruler. You'll find the focal length to be about 5 millimeters -- maybe more, maybe less. Can you estimate the magnification by measuring a known object (hair is about 70 microns in diameter)? Compare the width of the image with the diameter of your water lens which you can measure.

b) An improved water-drop magnifier. Take a stiff card 10 centimeters (cm) long and 3 cm wide - about the size of a microscope slide. Punch out or cut a hole about 5 mm wide (standard paper hole punch is 7 mm in diameter and maybe too big). Put a piece of clear plastic over the hole, tape it down, and then put a drop of water on the plastic over the hole with the droplet big enough to extend beyond the hole. Now you have a water-Leeuwenhoeck microscope. See if you can determine focal length and magnification.

Images of Nature

Go to Images of Nature and view optical microscopic images