- Illuminator.This is the light source located below the specimen.
- Condenser.Focuses the light through the specimen.
- Stage.The platform that holds the specimen.
- Objective.The lens that is directly above the stage.
- Nosepiece.The portion of the body that holds the objectives over the stage.
- Field diaphragm.Controls the amount of light into the condenser.
- Base.Bottom of the microscope.
- Coarse focusing knob.Used to make relatively wide focusing adjustments
to the microscope. - Fine focusing knob.Used to make relatively small adjustments to the
microscope. - Body.The microscope body.
- Ocular eyepiece.Lens on the top of the body tube. It has a magnification
of 10×normal vision.
MEASURING MAGNIFICATION
A compound microscope has two sets of lenses and uses light as the source of
illumination. The light source is called an illuminatorand passes light through
a condenserand through the specimen. Reflected light from the specimen is
detected by the objective. The objective is designed to redirect the light waves,
resulting in the magnification of the specimen.
There are typically four objectives, each having a different magnification.
These are 4×, 10×, 40×, and 100×. The number indicates by how many times the
original size of a specimen is magnified, so the 4×objective magnifies the spec-
imen four times the specimen size. The eyepiece of the microscope is called the
ocular eyepiece and it, too, has a lens—called an ocular lens—that has a magni-
fication of 10×.
You determine the magnification used to observe a specimen under a micro-
scope by multiplying the magnification of the objective by the magnification of
the ocular lens. Suppose you use the 4×objective to view a specimen. The image
you see through the ocular is 40×because the magnification of the object is mul-
tiplied by the magnification of the ocular lens, which is 10×.
Many microscopes have several objectives connected to a revolving nose-
piece above the stage. You can change the objective by rotating the nosepiece
until the objective that you want to use is in line with the body of the micro-
scope. You’ll find the magnification marked on the objective. Sometimes the
CHAPTER 3 Observing Microorganisms^55