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Microscope & Telescope Lab
Equipment:
Optical bench, 4 Carriages, Illuminated object lamp, 2 Lens holders, 3 Converging lenses
(5cm, 10 cm, 30 cm), Hooded screen, Flashlights.
A simple compound microscope is
constructed from two convex lenses
and is shown to the right . The first
lens is called the objective lens, and
the second, the eye piece. The
objective lens has a shorter focal
length than the eye piece. In
constructing and using a microscope,
the object is placed at a distance just
a little greater than the focal length
away from the objective lens. An
enlarged real image is then formed
on the other side of the objective
lens. An eye piece is then placed such that this image is just inside the focal length of the eye
piece, which means that the eye piece is acting as a magnifying glass that produces a final image
that is enlarged and virtual. Since the final image is virtual you cannot project it to determine its
final distance or image size. Thus, a ray diagram is used to find the final image distance and to
determine the total magnification. The overall magnification of a compound microscope is the
product of the individual magnifications of each lens:
M = Mo me = −
q1  25 cm 


p1  ƒe 
(1)
Diagrams for a telescope are shown to
the right, where the objective has a
longer focal length than the eyepiece.
The magnification for a telescope is given by ratio of
the objective to the eyepiece focal lengths:
(2)
m=
ƒ
θ
= − o
θo
ƒe
In today’s lab you will construct a simple microscope and telescope using two convex lenses and
determine the image location and magnification.
In sum, here is what you will be doing:
1. Measure the focal length of each of the three lenses.
2. Construct the telescope. Which lenses should you use to maximize the magnification?
Use those two and measure the distance between them. Sketch your setup showing where
the lenses, images, focal points, etc. are and labeling everything. Calculate the final
image location and the magnification. Show your calculations on the same page as the
drawing.
3. Construct the microscope. Which two lenses should you use to maximize the
magnification? Use those two and measure the distance between them. Sketch your setup
showing where the lenses, images, focal points, etc. are and labeling everything.
Calculate the final image location and the magnification. Show your calculations on the
same page as the drawing.
4. Based on your results, answer this: What is different/similar between a microscope and a
telescope? Type it up.