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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
Light source
Typically tungsten bulb, but now LED available | LED more expensive but lasts longer
26
Coloured glass filters
Used with lamps to reduce certain wavelengths of light. | Ex. Blue filter to reduce yellow light
27
Radiant Field Diaphragm
Controls the diameter of the light bundle directed at the specimen
28
Condenser Assembly
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
Aperture Diaphragm
controls the angle of the cone of light reaching the specimen
30
Slide controls
move stage in a horizontal plane, allowing viewing different areas of the slide
31
Focus knob
move stage in a vertical plane | Fine and course focus
32
Vernier scales
used to note particular location of an object on a slide | rulers on stage
33
Parfocal
nosepiece/objective assembly that allows the different objects to all focus the image at the same time
34
Mechanical Tube length
in mm | distance from top of ocular to the objective/nosepiece junction
35
Optical tube length
distance from optical centre of the objective lens to the focal plan of the ocular
36
Infinity corrected objectives
can be used on newer microscopes
37
Oculars
can be individually focused Typically made for 18mm field of view Hygenian (negative) Ramsden (positive)
38
Hygenian (negative) oculars
less expensive | less corrections for aberrations
39
Ramsden (positive) oculars
more expensive greater corrections for aberration Best used for micrometry (measuring)
40
Refraction
Bending of light due to change in medium Amount of refraction is based on: angle of incidence Refractive index of the mediums
41
Angle of Incidence (normal line)
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
Angle of incidence
the angle that the light strikes the surface
43
Angle of refraction
angle at which it leaves the surface
44
Light entering MORE DENSE medium
Bend TOWARDS normal
45
Light entering LESS DENSE medium
Bend AWAY from normal
46
Critical angle
Angle of refraction = 90degrees | Emerging ray will be parallel to the surface of the new medium
47
Total Internal Reflection
increase of angle of refraction past 90 degrees
48
Refractive index (RI or n)
``` 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
Snell's Law
RI = Sin(angle of incidence)/sin(angle of refraction)
50
Immersion oil
helps control refraction of light | prevents loss of light rays between slide and objective
51
Resolution
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
Wavelength
shorter wavelength=greater amount of refraction = greater separation of 2 points
53
Numerical aperture (NA)
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
Disadvantages to high NA
working distance, depth of field and flatness of field are all decreased
55
Useful magnification
occurs when 1000 X NA is greater than the total magnification
56
Empty magnification
occurs when 1000 X NA is less than the total magnification
57
Kohler
aligns microscope components to provide even illumination of specimen match NA of condenser assembly to NA of objective lens
58
Collector lens
focuses image of the light source at the focal plane of the condenser lens Light emerges as parallel rays
59
Radiant field diaphragm (RFD)
controls amount of light by controlling diameter of the light bundle
60
Setting Kohler steps
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
Infinity Corrective Objectives
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
Common objective markings
- 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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