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Lab 3: Build a Telescope

Virtual Images and the Telescope



In this lab, we examined how a refracting optical telescope functions to produce a real image or virtual image. Varying lens type, distance from the lens to the lens and the background on which the image was produced, we observed how the image size, distance to focus, and image orientation changed.


Terms and Definitions

Real Image: Can exist even if no observer is present (object is farther than the focal length) Can be projected so that multiple people can see the image, even if the image disappears.
Virtual Image: Requires the visual system of an observer (object is closer to the lens than the focal length) Cannot be projected
Focal Distance: Distance between the lens and the point where the light rays converge
Magnification: A vector quantity used to determine the degree at which a visual object is magnified
Concave: A surface that curves in on itself like the interior of a circle
Double Concave Lens: A lens with a concave curve on both sides.


Overview of Lab

By using multiple lenses, extra magnification of an object could be achieved with the same amount of clarity.

The purpose of the lab was to discover the properties of light through multiple lenses. A refracting optical telescope was built to solidify an understanding of real and virtual images and examine magnification through virtual images.



When Image is Most Focused

Lens Type/Setup Distance from Lens to Film when Image is Focused Observations
10 cm double convex 8.5 cm Virtual
10 cm double convex + 20 cm double convex, telescope set up 10 cm to film: 8 cm
Film to 20 cm: 20 cm
Virtual, larger image
20 cm double convex + 10 cm double convex, telescope set up 20 cm to film: 8 cm
Film to 10 cm: 9.5 cm
Real iamge, looks better, glowy, smaller image
Two 20 cm double convex lenses, telescope set up 10 cm to film: 11 cm
Film to 20 cm: 20 cm
Virtual, large, focused

Analysis: The larger the lens size, the greater the magnification.

Extension: Galilean Telescopes

A galilean telescope is a telescope which uses both a positive objective and a negative eye lens which are positioned based on the difference of their two focal distances. The second negative lens is placed in an arrangement so the second focal point occurs where the second focal point of the objective lens occurs.


Analysis and Conclusion

Using multiple lenses we made a galilean telescope. First we investigated virtual images and magnifying lenses. Then we learned about the relationship between magnification and real images. Finally we used our virtual images and magnification understanding to build a telescope that allowed us to see objects from greater distance with clarity. We realized that a galilean telescope simply creates a real, upside down image with a convex lens, then uses another convex lens to create another real image of that first real image. This combination concentrates the light and magnifies the object.



We experimented with our homemade telescope to really experience what we had made.
This is the setup of our Galilean telescope. It is composed of two convex lenses and a screen.