Microscope Definitions Flashcards
Refractive index
Measure of how much a substance slows velocity of light
Focal point
Point a lens focuses light on
Focal length (f)
Distance from the center of the lease to the focal point.
Humans can’t see objects closer than?
25cm
Lens strength and Focal length
Higher lens strength = shorter focal length
Bright field microscope
Bright background with a darker image of the sample
Condenser lens
Below stage, focuses light on sample
Parfocal
Keeps image in focus when objective lenses are changed
Magnification
Product of ocular and objective power
Resolution
Ability of a lens to distinguish two objects from each other
Numerical aperture
N sin theta n=refractive index theta= half angle of the cone of light entering objective
Diameter of smallest resolvable particle
= 0.5 wavelength of light / numerical aperture.
(Smaller this is the better resolution and finer detail observed)
What is needed for fine detail characterization?
High quality magnification & resolution (high aperture)
Darkfield Microscopy
Produces bright objects against a bright field (only light refracted by specimen enters objective due to hollow cone of light)
Phase contrast Microscopy
Relies on change of velocity of light in different media as it passes through the sample.
Phase contrast microscope most useful for?
Living samples; creates contrast without staining
Condenser annulus
Directs ring of light to the condenser
Phase plate
Focuses undeviated light and advances by 1/4 wavelength to create required 1/2 wavelength separation between deviated and undeviated light
Fluorescence microscopy
Excites a specimen with a specific wavelength of light, triggers the specimen to emit light
Fluorochromes
Fluorescent dyes used to tag specific cells or parts of cells so that they emit light at a specific wavelength.
Confocal microscopy
Used laser beam to illuminate a fluorescent sample and remove stray light to produce higher resolution images
Fixation
Process used to fix and preserve the internal and external structures of a sample
Heat fixation
Application of heat to preserve and rice sample cells to a slide
Chemical fixation
Use of chemicals to fix a specimen. Protects fine cellular structure better than heat fixation, often used for electron microscopy
Capsule staining
Negative staining that illustrates the presence of a capsule ( stains are acidic so stain background revealing a halo if capsule is present)
Flagella staining
Increases thickness of flagella with tannic acid or potassium alum to thicken flagella enough that they are visible with light scope
Max resolution limit of light scope
0.2 micrometers
Electron microscopy
Uses electrons as the illuminating beam. (Roughly 1000 times better resolution than light scope)
Transmission electron microscope
Form image from radiation passed through the specimen. Uses electro magnets to focus instead of glass
Scanning electron microscope
Produces an image from electrons reflected from an objects surface
