MICROSCOPE Flashcards
A lab instrument used to view and examine objects that are too small to be seen by the
naked eye.
Microscope
Light coming from a light source (mirror or bulb) will travel through the
specimen
The light hitting the specimen will be focused (concentrated) by a lens or set of lenses called
objectives
The focused light will now travel the tube/body through the ________ which further increases the magnification
eyepiece
final image that an observer sees when viewing a microscope
virtual image
virtual image can be affected by many factors, which can also be manipulated to get better quality images. Some of these factors are:
● The type of light (electromagnetic spectrum) used
● The properties or size of the object being observed
● Lens type and placement
● Contrast
The degree on how a device can enlarge an object/specimen. In microscopes, this is provided by the lens.
Magnification
Total magnification formula
(Objective magnification) x (Eyepiece magnification)
Ability of a microscope to differentiate two adjacent objects as discrete entities
Resolution
wavelength of light and numerical aperture (NA)
Resolution
Resolving power formula
wavelength / 2 x Numerical aperture
dictates the light gathering ability of the objective and the condenser
Numerical aperture
Numerical aperture formula
= n sin (theta), where n = refractive index
Measure of the bending of light as it passes from one medium to another
Refractive index
Lights bends as it passes through the glass side which can cause
light dispersion
can be used to lessen dispersion as it has same index as glass in higher magnification
oil
Light source e.g., mirror or light bulb
Illumination
collects the light from the light source and form into a cone of light that is focused on the
specimen
Condenser
Used to adjust the size of the opening (aperture) in which the light passes through before reaching the condenser
Diaphragm
During observation, most microscope objectives can be switched with minimal refocusing
Parfocality of Microscopes
maintain focus even when focal length is changed
Parfocal lenses
Interaction of the light and the specimen
Adding contrast between the specimen and the background can aid in the viewing the details of the specimen.
Contrast
Electron Microscope
Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)
specimens are visualized because of differences in contrast (density) between the specimen and surrounding.
Uses two set of lenses (objective and ocular)
Maximum magnification ~ 2,000X
Bright Field Microscope
Uses a phase ring
creates contrast without the use of dyes
Live samples can be observed
Dark cells on light background
Phase Contrast Microscope
it can induce phase shifts due to brightness variation
phase ring
Light from light source is blocked of thus light reaches the specimen from the side
Best for observing motility
Dark Field Microscope
Visualize specimens that fluoresce
Fluorescence can be natural or
induced (through staining e.g. using
DAPI)
Used in microbial ecology for enumeration of bacterial population
Fluorescence Microscope
emit light when it absorbs other wavelengths of light
fluoresce
Uses polarizer w/c creates two distinct beams of polarized light
The polarized light can make some cell structure (e.g. vacuole, endospores, etc.) appear 3D
Differential Interference Contrast (DIC) Microscopy
Computerized microscope + laser source
The computer focuses the laser on single layers of the specimen
Resolution is 0.1 μm
Confocal Scanning Laser Microscope (CLSM)
Electromagnets serves as lenses
High magnification and high resolution
(0.2 nm)
Requires a vacuum and specimens
should be sliced thinly (20-60 nm)
Transmission Electron Microscope (TEM)
stain used for Transmission Electron Microscope (TEM)
uranyl acetate and lead citrate
Beams of electron hits heavy metal coated specimen
heavy metal coat is used
The electrons that will scatter will hit the detectors rendering an image
Magnification 15x to 100,000 x
Scanning Electron Microscope (SEM)
