College Physics Lab
PH 144
Combinations of Lenses
Telescopes and Microscopes
Purpose: To study the formation of images by a combination of lenses. To make a simple telescope and
microscope.
Discussion: The formation of an image by multiple lenses is described by the separate effect of each lens.
The image created by one lens becomes the object for the next lens, etc. We still use the thin lens formula
and magnification formula for each lens.
=+
m==
However, it will be necessary to distinguish the object distance, image distance, focal length and
magnification (do1, di1, f1, m1) for the first lens from the object distance, image distance, focal length, and
magnification (do2, di2, f2, m2) for the second lens. You will know f1 from a previous experiment. Lens 2
will be chosen such that f2 is greater than f1.
Procedure:
1. Arrange the object and lens 1 such that do1 is slightly less than f1. In this case there is no real image, but
you may be able to observe a virtual image by looking through the lens towards the object.
2. Use the thin lens formula to calculate di1. Note that di1 should be negative and relatively large in
absolute value. Calculate m1 the theoretical magnification for lens 1. Note that m1 should be positive since
the image is upright.
3. The virtual image created by the first lens is the object for the second lens. Without moving the first
lens, use the second lens to create a real, inverted image.
4. Use the calculated value for di1 and the known distance between the lenses to calculate d o2. Use the
position of lens 2 and the final image to calculate di2.
5. Use do2 and di2 to calculate f2 (using the thin lens formula) and m2.
6. Measure the height of your original object and your final image, and calculate the total magnification.
Is it the same as the product (m1)(m2)? Calculate the percentage error.
7. Make a ray diagram of this two-lens system.
8. Using 2 lenses from lenses available, make a telescope and a microscope as described on pages 783-785
of your textbook.