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NatureMapping Activities

4: Using Binoculars/Monoculars.

To learn about magnification and field of vision and the use of binoculars and monoculars when observing wildlife.

Materials Needed:

  • How to use binocular's guide (pdf)
  • Binoculars
  • Monoculars
  • Posters of animals in their habitat.
  • Stopwatches or a clock with sweeping second hand.

Teacher’s Guide:

  1. Review notes in preparation to teach students.
  2. Place posters at various locations in the room.
  3. Group students in teams of three.
  4. One person will stand close enough to a poster to be able to select an animal with the naked eye. He/she will describe the animal. The team member using the binoculars and the team member using the monocular will find the animal. Both start at the same time. Record the difference between each in finding the animal. Change places within your team and repeat until each team member has had the opportunity to use each scope.

Teachers Notes:

    Predator & Prey

    Importance of magnification, light-gathering power, stereoscopic and monocular vision to predators and prey. Some birds of prey have stereoscopic vision - they use both eyes to focus on prey.

    Peregrine falcons eyeballs change shape when they are closing in at almost 200 mph after prey. Eagles can see prey almost 2 miles away. The lens in their eyes have high magnification powers, just like the binoculars the Coast Guard uses to read ship names very far away.

    Another bird of prey, the owl, finds its prey in the dark. It needs light-gathering power more than magnification to be successful. Owl eyes are very large, gathering much light

    Pigeons and other prey species need a large field of vision in order to watch for predators. Their eyes are placed on either side of their head. Pigeon eyes are monocular. Each eye can focus independent of the other eye.

    Prey animals often stay in large groups so there are more eyes watching for predators. Prey animals have survival techniques that allow them to escape if caught. The pigeon has quick release feathers. Unless a Peregrine falcon has a good grip on the body of a pigeon it will have a bunch of feathers in its talons and the pigeon will escape.


Binoculars Diagram by Jason O'Brien

Understanding Range of Power.
    A higher powered lens will give greater magnification. However, the ability to hold steady on an object decreases with increased magnification.
    Range of Power

    Range of Power
    The larger diameter allows a greater amount of light to enter. The diameter of the lens refers to the Field of Vision. Click on picture to see effect of a change in lens diameter..
      Field of Vision

      Field of Vision diagram
Questions to test student understanding;
  • What size will allow you to see the farthest 8 x 21 or 10 x 21? (Answer: 10 x 21 -- 10 is the higher magnification.)
  • If you are in the forest and need to see up into the branches, which size would you choose, 10 x 21 or 8 x 40? (Answer: 8 x 40 -- the magnification may be lower, but more light will allow you to see better.



zoom 1   zoom 1   zoom 1  
Using a higher magnification (10x) you can identify birds from a distance.

Field of View

Wide Angle vs. Standard Lens

wide angle of view        narrow angle of view
Using a wide angle lens (left), you can see more in the field of view than with a standard lens (right).
The wide angle lens makes it easier to scan for wildlife in the field.


No Student Guide


Binoculars - an optical instrument with a separate lens for each eye, used for viewing distant objects.

Habitat - the type of environment in which an organism or group normally lives

Magnification - the ratio of the size of an image to the size of the object

Monocular vision - vision with only one eye

Stereoscopic vision - three-dimensional vision produced by the fusion of two slightly different views of a scene on each retina

Talons - the sharp nails on the foot of a bird which it uses when hunting animals

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