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MEDL-210 MB > Module 2: Microscopy > Flashcards

Module 2: Microscopy Flashcards

1
Q

Convex

A

Positive
causes light rays to converge
Magnification is related to curvature of lens surface

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2
Q

Concave

A

Negative (thinner in center)
Causes light rays to Diverge
Not used for magnification

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3
Q

Focal Point

A

point at which parallel light rays converge after passing through a convex lens

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4
Q

Focal Length (F)

A

distance from the centre of the lens to the focal point

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5
Q

Focal Plane

A

vertical plane the focal point lies within

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6
Q

Lens with larger diameter and flatter lens faces

A

result in longer focal lengths

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7
Q

Smaller lens with rounder lens faces

A

Result in shorter focal lengths (and more magnification than larger lens)

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8
Q

Working distance

A

distance from specimen to the objective lens

Higher magnification objective = shorter working distance

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9
Q

Depth of field

A

range in which an object is in focus

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10
Q

Conjugate foci

A

for convex lenses

The object and its formed image

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11
Q

When object is greater than 2 focal lengths from the lens

A

The image will be:
REAL
SMALLER
INVERTED

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12
Q

When object is exactly 2 focal lengths away from the lens

A

The image will be:
REAL
SAME SIZE
INVERTED

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13
Q

When object is between 1-2 focal lengths from the lens

A

The image will be:
REAL
MAGNIFIED
INVERTED

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14
Q

When object is exactly 1 focal length from the lens

A

Light rays emerge from lens in parallel

Image can no longer be focused

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15
Q

When object is less than 1 focal lengths from the lens

A 
The image will be:
on the same side as the object (can only be seen by looking through the lens)
VIRTUAL
MAGNIFIED
ERECT
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16
Q

Compound microscope

A

Primary magnification made by the objective lens
Object on stage is 1-2 focal lengths from the lens (real, magnified, inverted)
Image formed by objective lens is focused inside the microscope tube.
Image and ocular lens are less than 1 FL apart (image we see if virtual, magnified and erect)

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17
Q

Total magnification

A

multiply magnification of objective lens and ocular lens
OR
Total mag = mag of ocular X (tube length/objective focal length)

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18
Q

Chromatic Aberration

A

White light passes through lens, shorter wavelengths are refracted more than longer wavelengths
Different wave lengths will have different focal points
Produces distortion in the colors of the image
May produce a fringe of colors around the periphery of the field

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19
Q

Spherical Aberration

A

Light passing through the centre of the lens does not bend as much as rays passing through edge of lens
Outer edges will be blurred

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20
Q

Corrections for chromatic aberration (3)

A

Achromatic Lenses $
Semi-apochromats (fluorites) $$
Apochromats $$$

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21
Q

Achromatic Lenses

A

Corrective lense for chromatic aberration
Least expensive
Corrected for red and blue

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22
Q

Semi-apochromats (fluorites)

A

Corrective lense for chromatic aberration
Moderately expensive
Incorporate fluorite into lens to correct for red, blue, and SOME green

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23
Q

Apochromats

A

Corrective lense for chromatic aberration
Most expensive
Correct all 3 colors (red, blue, green)

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24
Q

Corrections for Spherical Aberration

A

Combined use of convex and concave lenses
Combined lense produces flat fields of view
Termed:
“plan-“
ex. plan-apochromats

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25
Q

Light source

A

Typically tungsten bulb, but now LED available

LED more expensive but lasts longer

26
Q

Coloured glass filters

A

Used with lamps to reduce certain wavelengths of light.

Ex. Blue filter to reduce yellow light

27
Q

Radiant Field Diaphragm

A

Controls the diameter of the light bundle directed at the specimen

28
Q

Condenser Assembly

A

Lens system located between light source and specimen in the light path (right below stage assembly)
Acts to focus the illuminating light onto the slide on the stage

29
Q

Aperture Diaphragm

A

controls the angle of the cone of light reaching the specimen

30
Q

Slide controls

A

move stage in a horizontal plane, allowing viewing different areas of the slide

31
Q

Focus knob

A

move stage in a vertical plane

Fine and course focus

32
Q

Vernier scales

A

used to note particular location of an object on a slide

rulers on stage

33
Q

Parfocal

A

nosepiece/objective assembly that allows the different objects to all focus the image at the same time

34
Q

Mechanical Tube length

A

in mm

distance from top of ocular to the objective/nosepiece junction

35
Q

Optical tube length

A

distance from optical centre of the objective lens to the focal plan of the ocular

36
Q

Infinity corrected objectives

A

can be used on newer microscopes

37
Q

Oculars

A

can be individually focused
Typically made for 18mm field of view

Hygenian (negative)
Ramsden (positive)

38
Q

Hygenian (negative) oculars

A

less expensive

less corrections for aberrations

39
Q

Ramsden (positive) oculars

A

more expensive
greater corrections for aberration
Best used for micrometry (measuring)

40
Q

Refraction

A

Bending of light due to change in medium
Amount of refraction is based on:
angle of incidence
Refractive index of the mediums

41
Q

Angle of Incidence (normal line)

A

normal line is 90 degrees relative to the surface
light will pass straight through the normal line without refracting
Light ray angles are measures from the “normal” pathway

42
Q

Angle of incidence

A

the angle that the light strikes the surface

43
Q

Angle of refraction

A

angle at which it leaves the surface

44
Q

Light entering MORE DENSE medium

A

Bend TOWARDS normal

45
Q

Light entering LESS DENSE medium

A

Bend AWAY from normal

46
Q

Critical angle

A

Angle of refraction = 90degrees

Emerging ray will be parallel to the surface of the new medium

47
Q

Total Internal Reflection

A

increase of angle of refraction past 90 degrees

48
Q

Refractive index (RI or n)

A 
expression of the density of a medium
Denser medium = slower light rays = higher RI
Air = 1.00
Crown glass = 1.52
Immersion oil = 1.52
49
Q

Snell’s Law

A

RI = Sin(angle of incidence)/sin(angle of refraction)

50
Q

Immersion oil

A

helps control refraction of light

prevents loss of light rays between slide and objective

51
Q

Resolution

A

Minimum distance 2 objects must be apart in order to be seen as distinct
Depends on wavelength of light used and numerical aperture of the lens
Resolution = λ/2NA

52
Q

Wavelength

A

shorter wavelength=greater amount of refraction = greater separation of 2 points

53
Q

Numerical aperture (NA)

A

expression of the ability of a lens to gather light
(cone of light from slide to objective)
Wider cone (higher NA) = better resolution
NA = n sin μ
n=refractive index of the medium between the object and the lens
μ = one half the angle of aperture
NA for oil lens (100X) = 1.25
NA of condenser should match NA of objective for best resolution

54
Q

Disadvantages to high NA

A

working distance, depth of field and flatness of field are all decreased

55
Q

Useful magnification

A

occurs when 1000 X NA is greater than the total magnification

56
Q

Empty magnification

A

occurs when 1000 X NA is less than the total magnification

57
Q

Kohler

A

aligns microscope components to provide even illumination of specimen
match NA of condenser assembly to NA of objective lens

58
Q

Collector lens

A

focuses image of the light source at the focal plane of the condenser lens
Light emerges as parallel rays

59
Q

Radiant field diaphragm (RFD)

A

controls amount of light by controlling diameter of the light bundle

60
Q

Setting Kohler steps

A

Raise condenser
Open condenser aperture
Close radiant field diaphragm
Lower condenser until image is in sharp focus
Centre using centering screws
Open field diaphragm until field is completely filled with light
Remove ocular, close condenser aperture until light field is 75% open

61
Q

Infinity Corrective Objectives

A

Will have infinity symbol instead of tube length
Must be used with a microscope that has a tube lens
Allow for other components to enter light path (ex. filters)

62
Q

Common objective markings

A
  • oil immersion
  • apochromat
  • 100x magnification
  • 1.25 NA
  • 170mm tube length
  • Coverslip thickness not important

Oil/Apo
100/1.25
170/-

MEDL-210 MB (13 decks)

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