Microscopes Flashcards

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1
Q

Objective lens

A
  • short focal length/group of lenses
  • biggest part of the magnification of the microscope
  • some lenses remove optical defects of the frontal lens (distortion, chromatic aberration)
  • forms true real magnified image
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2
Q

Eyepiece lens

A

Ocular

  • two spherical lenses
  • forms large virtual image
  • final image virtual, magnified and reversed
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3
Q

Optical condenser

A
  • collimate the light beam of the light source and to focus it onto the object
  • contributes to quality of image
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4
Q

Magnification

A

ratio of the linear dimensions of the image and of the object

  • magnification of the optical microscope Wm is given by the product of the linear magnification of the objective Wobj and the angular magnification of the eyepiece Woc

Wm = Wobj x Woc

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5
Q

Resolution

A
  • ability to distinguish neighbouring objects
  • smaller distance, able to distinguish, larger resolution
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6
Q

Distance d, in the optical microscope

A
  • is defined by the size and the position of the frontal lens of the objective
  • by the refractive index n, of the medium between the frontal lens and the object
  • and by the wavelength of the light illuminating the object

d = 0.61 x λ/n.sinα
α - half maximal angle between the incident beam and frontal lens of the objective = aperture angle

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7
Q

Numerical aperture

A

A = n sin α

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8
Q

Refractive index

A

dry object, vacuum, air, = 1

  • if space between frontal lens of the objective and the investigated object is filled with a substance with n>1, d decreased and resolution increases
  • substance used = immersion liquids, cedar oil n=1.52
  • necessary when microscope has high magnification
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9
Q

Dark field observation

A
  • used when investigated object is small, transparent, and unstained
  • when it strongly disperses the incident light
  • light transmitted by object is minimised and only light dispersed by object falls on objective
  • object seen bright
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10
Q

Phase contrast observation

A
  • used when object is unstained and contains structural elements with different n’s
  • inserting suitable rings in condenser and objective, difference between n is transformed into an amplitude difference thus increasing contrast
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11
Q

Observation with polarised light

A
  • suitable for investigation of a transparent unstained object containing optically active structures
  • object placed between polariser and analyser of the polarising microscope only the optically active structures are visible
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