PASCO OS-8515C Basic Optics System User Manual
Page 68
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B a s i c O p t i c s S y s t e m
T e a c h e r ’ s G u i d e
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Further study, Image Formed by the Objective Lens:
The objective lens forms a real, upright image;
to see it, hold a sheet of paper at distance d
i1
from the objective. When a pencil is placed at this location, it’s vir-
tual image, viewed through the eyepiece lens, coincides with the virtual image of the grid pattern viewed through
both lenses.
Further study, Increasing Magnification:
As the objective lens is moved closer to the object, the eye-
piece must be moved further away. In practice, the objective can be moved to within about 13 cm before distor-
tion from lens aberrations becomes significant. The theoretical limit is 10 cm, or the focal length of the objective
lens.
When the pencil is illuminated by the point source, the shadow appears sharper than when illuminated by a dis-
tributed light source (the crossed-arrow object). When illuminated by both point sources, the pencil casts two
shadows. The area where the shadows overlap is the umbra. The areas of partial shadow are the penumbra. By
moving the pencil toward the screen, the relative size of the umbra is increased. By moving the pencil away from
the screen, the umbra is decreased until the two shadow separate entirely.