EXERCISE 3. THE MICROSCOPE
TYPES OF MICROSCOPES
COMPARE AND CONTRAST THE FOLLOWING TYPES OF MICROSCOPES
1. LIGHT MICROSCOPES
LIGHT MICROSCOPES USE VISIBLE LIGHT TO ILLUMINATE SAMPLES AND
MAGNIFY THEM THROUGH LENSES.
A. COMPOUND MICROSCOPE
 USES MULTIPLE LENSES TO MAGNIFY SAMPLES; TYPICALLY INCLUDES
AN OBJECTIVE LENS AND AN EYEPIECE AND UP TO 1000X TO 2000X
MAGNIFICATION
 COMMONLY USED IN BIOLOGY AND MEDICINE FOR VIEWING CELLS,
TISSUES, AND MICROORGANISMS.
B. BRIGHT-FIELD MICROSCOPE
 A TYPE OF COMPOUND MICROSCOPE THAT ILLUMINATES THE SPECIMEN
DIRECTLY WITH A LIGHT SOURCE.
 GENERALLY PROVIDES LOW CONTRAST FOR TRANSPARENT SPECIMENS;
STAINS ARE OFTEN REQUIRED TO IMPROVE VISIBILITY.
 SUITABLE FOR OBSERVING STAINED SAMPLES; COMMONLY USED IN
HISTOLOGY.
C. DARK-FIELD MICROSCOPE
 USES A SPECIAL CONDENSER TO SCATTER LIGHT, ILLUMINATING THE
SPECIMEN INDIRECTLY.
 PRODUCES A BRIGHT IMAGE ON A DARK BACKGROUND, ENHANCING THE
VISIBILITY OF SMALL, TRANSPARENT SPECIMENS.
 EFFECTIVE FOR OBSERVING LIVE MICROORGANISMS AND THIN
SPECIMENS WITHOUT STAINING.
D. PHASE CONTRAST MICROSCOPE
 ENHANCES CONTRAST BY CONVERTING PHASE SHIFTS IN LIGHT PASSING
THROUGH THE SPECIMEN INTO CHANGES IN AMPLITUDE.
 ALLOWS FOR THE VISUALIZATION OF TRANSPARENT SPECIMENS
WITHOUT STAINING, MAKING INTERNAL STRUCTURES MORE VISIBLE.
 COMMONLY USED IN MICROBIOLOGY AND CELLULAR BIOLOGY FOR LIVE
CELLS AND ORGANISMS.
E. ULTRAVIOLET MICROSCOPE
 USES ULTRAVIOLET LIGHT FOR ILLUMINATION, WHICH CAN PROVIDE
HIGHER RESOLUTION THAN VISIBLE LIGHT.
 FLUORESCENCE IS INDUCED IN CERTAIN MATERIALS, ENHANCING
CONTRAST AND ENABLING THE OBSERVATION OF SPECIFIC
COMPONENTS.
 USEFUL IN STUDYING FLUORESCENCE AND PHOTOMICROGRAPHY;
OFTEN USED IN MOLECULAR BIOLOGY.
F. FLUORESCENCE MICROSCOPE
 EMPLOYS FLUORESCENCE AND PHOSPHORESCENCE INSTEAD OF, OR IN
ADDITION TO, REFLECTION AND ABSORPTION.
 ALLOWS SPECIFIC LABELING OF STRUCTURES WITHIN THE CELL WITH
FLUORESCENT DYES, ENABLING HIGH CONTRAST IMAGES.
 WIDELY USED IN CELL BIOLOGY FOR VISUALIZING PROTEINS, DNA, AND
OTHER CELLULAR COMPONENTS.
2. ELECTRON MICROSCOPES
ELECTRON MICROSCOPES USE ELECTRON BEAMS INSTEAD OF LIGHT TO
ILLUMINATE SAMPLES, ALLOWING FOR MUCH HIGHER RESOLUTION. THE KEY
TYPES INCLUDE:
A. TRANSMISSION ELECTRON MICROSCOPE (TEM)
 USES A BEAM OF ELECTRONS TRANSMITTED THROUGH A VERY THIN
SPECIMEN TO CREATE AN IMAGE AND CAN ACHIEVE MAGNIFICATIONS OF
UP TO 1,000,000X.
 PROVIDES DETAILED INTERNAL STRUCTURE OF CELLS AND
ORGANELLES; USED IN MATERIALS SCIENCE AND NANOTECHNOLOGY.
B. SCANNING ELECTRON MICROSCOPE (SEM)
 SCANS A FOCUSED ELECTRON BEAM ACROSS THE SURFACE OF A
SPECIMEN TO PRODUCE A THREE-DIMENSIONAL IMAGE AND TYPICALLY
UP TO 100,000X BUT WITH HIGH DEPTH OF FIELD.
 IDEAL FOR OBSERVING THE SURFACE MORPHOLOGY AND TOPOGRAPHY
OF SAMPLES; USED IN BIOLOGY, MATERIALS SCIENCE, AND
ENGINEERING.
C. SCANNING TUNNELING MICROSCOPE (STM)
 USES A CONDUCTING TIP THAT SCANS THE SURFACE AT THE ATOMIC
LEVEL BY MEASURING THE TUNNELING CURRENT BETWEEN THE TIP AND
THE SURFACE AND CAN ACHIEVE ATOMIC RESOLUTION.
 PRIMARILY USED IN SURFACE SCIENCE TO VISUALIZE AND MANIPULATE
ATOMS AND MOLECULES; IMPORTANT IN NANOTECHNOLOGY AND
MATERIALS SCIENCE.