mark is color-coded and other times the magnification is etched into the side
of the objective.RESOLUTION
The area that you see through the ocular eyepiece is called the field of view.
Depending on the total magnification and the size of the specimen, sometimes
the entire field of view is filled with the image of the specimen. Other times,
only a portion of the field of view contains the image of the specimen.
You probably noticed that the specimen becomes blurry as you increase mag-
nification. Here’s what happens. The size of the field of view decreases as mag-
nification increases, resulting in your seeing a smaller area of the specimen.
However, the resolution of the image remains unchanged, therefore you must
adjust the fine focus knob to bring the image into focus again.
Resolutionis the ability of the lens to distinguish fine detail of the specimen
and is determined by the wavelength of light from the illuminator. At the begin-
ning of this chapter you learned about the wave cycle, which is the process of
the wave going up and then falling down time and again. A wavelength is the
distance between the peaks of two waves. As a general rule, shorter wavelengths
produce higher resolutions of the image seen through the microscope.CONTRAST
The image of a specimen must contrast with other objects in the field of view or
with parts of the specimen itself to be visible in different degrees of brightness.
Suppose the specimen was a thin tissue layer of epidermis. The tissue must be a
different color than the field of view, otherwise the tissue and field of view
blend, making it impossible to differentiate between the two. That is, the tissue
and the field of view must contrast.
Previously in this chapter you learned that what you see is light reflected by
the specimen (or the transmitted light if the specimen doesn’t absorb light).
The illuminator shines white light onto the specimen. White light contains all
the light waves in the visible spectrum. The specimen absorbs some of the
light waves and reflects other light waves, giving the appearance of some color
other than white.
Light waves that are reflected by the specimen are measured by the refractive
index. The refractive indexspecifies the amount of light waves that is reflected
by an object. There is a low contrast between a specimen and the field of view if(^56) CHAPTER 3 Observing Microorganisms