Module 2: Microscopy Flashcards
Convex lenses
Thicker in the centre
Light rays converge
Positive lenses
Concave lenses
Thinner in the centre
Light rays diverge
Negative lenses
Used to correct for aberrations
Focal length
Distance from the centre of the lens to the focal point
Working distance
Distance from the specimen to the objective lens
Depth of field
Range in which an object is in focus
Real image
Object is >1 focal length from lens
Image on opposite side of lens and can be focused on a screen
Inverted
Virtual image
Object within 1 focal length
Image on same side of lens
Magnified and erect
Must be viewed through a lens
Microscope component that magnifies the object and produces a real image
Objective lens
Microscope component that magnifies the real image
Ocular lens
Chromatic aberration occurs because
Shorter wavelengths are refracted more than longer wavelengths
Spherical aberration occurs because
Light passing through the centre of the lens does not bend as much as those passing through the periphery
Chromatic aberration causes
Distortion of colours
Spherical aberration causes
Blurry image
Three types of objectives with correction for chromatic aberration
Achromats, semi-apochromats, apochromats (best)
Lenses that are corrected for spherical aberration have the designation:
Plan
Microscope component that controls the size of the light bundle striking the specimen
Radiant field diaphragm
Microscope component that focuses light on the specimen
Condenser assembly
Microscope component that controls the size of the cone of light striking the specimen
Condenser aperture diaphragm
Distance from the optical centre of the objective lens to the focal plane of the ocular
Optical tube length
Distance from the top of the ocular to the objective/nosepiece junction
Mechanical tube length
Hygenian and Ramsden are types of:
Oculars
Abbe and Aplanatic-achromatic are types of:
Condensers
The bending of light rays as they pass through different media is termed:
Refraction
The amount of refraction depends on
Angle of incidence and refractive index of mediums
Critical angle
The angle at which light is unable to leave a more dense medium for a less dense medium
Resolution is dependant upon two factors:
Wavelength of light used
Numerical aperture
Numerical aperture
Mathematical expression of the light gathering ability of a lens
Higher = better resolution
Three disadvantages to high numerical aperture lenses
Decreased working distance
Decreased depth of field
Decreased flatness of field
Calculation of total magnification
mag of ocular x tube length/objective focal length
Useful magnification
1000 x NA is greater than the total magnification
Empty magnification
1000 x NA is less than the total magnification
The limit of useful magnification is exceeded
Kohler illumination
Produces even illumination of the specimen
Matches the numerical aperture of the condenser to the objective lens
