3.2 Microscope
A magnifield image of a small object (stage micrometer and
micro-slide of a dog flea) is produced with a lens L1 of short
focal length ƒ1 = +20 mm. The real intermediate image is
observed through an eyepiece L2 (ƒ2 = +50 mm) (Fig. 4). The
ground glass and the object holder with the object are fixed in
the swinging arm. L1 is brought as close to the object as possible.
The object is illuminated through a ground glass screen.
The size of the image and thence the overall magnification are
roughly determined by comparing it with a scale at the least
distance of distinct vision (approximately 25 cm). To do this
we look through the microscope with the right eye and at the
scale with the left. With practice the two images can be superimposed.