26 PART I Basics of Microscopy
well as the refractive index of the medium between objective’s front lens and
sample surface can influence the resolution.
About Stick Insects and Contrast
Some animals are really masters of camouflage. Think about a stick insect hanging
in the branches of a tree, or a chameleon. They use the effect of – let’s call it
anti-contrast – for their survival. What does that mean for microscopy? The answer
is the contrast! The contrast is what allows the human eye to distinguish patterns
and shapes from a background relative to the light intensity of the background.
Without contrast in intensity and/or colors, the object is invisible for
your eyes even under adequate resolution and magnification. In general, a minimum
contrast value of 2% is needed by the human eye to distinguish differences
between
the image and its background. In microscopy, you can improve the contrast
by proper sample preparation and using contrasting techniques (read more
about this in Parts II and III).