Lecture 2 Jan 29 2018 Flashcards Preview

Instrumentation of Trace Evidence > Lecture 2 Jan 29 2018 > Flashcards

Flashcards in Lecture 2 Jan 29 2018 Deck (93):
1

The term microscopy used to describe:

Analytical approach in which a microscope plays a central role in maximizing extraction of useful information from a variety of samples.

2

Identification (ID) of general unknown is greatly facilitated with a______________________.

Preliminary Microscopical Examination

3

Applications of the microscope in forensics include:

- Document examination
- Tool mark comparison
- Firearms ID
- Serology
- Drug chemistry
- Trace evidence

4

Microscope used as a symbol of science but seems less exotic than recent instrumentation, in some cases____________________.

old fashioned

5

________________and______________are the two main purposes of a microscope too create an enlarged image of an object that is clear and distinct.

Magnification
Resolution

6

Magnification and resolution conflict with each other:

As magnification increases, resolution can decrease

7

Greater resolution means greater detail, while greater magnification means ________________.

Larger image

8

A converging (also known as positive )lens can form images in two ways:

Real image
Virtual image

9

____________ is formed on the side of the lens opposite the object and is inverted with respect to object, light rays converge at a given plane in space and thus image falls on the screen.

* slide projector

Real image

10

_____________is when a lens is used as a magnifying glass; rays from this type appear to diverge from a plane on the same side of the lens as the object:
* Use of another lens is necessary to convert virtual into real
* When virtual image is examined visually, the lens of the eyes serves this function so that real image is projected onto the retina

Virtual image

11

___________________ distance from the lens to the principle focus (for thin lens).

Focal length

12

If an object placed at infinity, the image will form at:

Principle focus

13

If object placed at principle focus, image will form at _____________.

Infinity

14

_________ of a simple lens is defined by a straight line running through the centers of curvatures of the two surfaces.

Axis

15

The on axis point object at infinity on left side of lens, the lens will form real image in the right-hand space known as:

Principle focus of the lens

16

_____________(for thick lenses) measured from the image for an object at infinity (focal point for incident rays parallel to lens axis) to nearest principle plane.

Equivalent focal length

17

Magnification (M) for a real image can be defined by the equation:

M = Q/P

18

If, P=2F=Q, magnification is:

1

19

If P>Q, then M<1 :

Means there is a reduction

20

If P1:

We have conditions for magnification by microscope objective

21

__________________the departures in performance between actual and hypothetical ideal simple lens.

* Aberrations do not rise from defects introduced from manufacturing process
* Inherent even in perfectly made simple lens

Aberrations

22

The variation of focal length with distance from the lens axis is called__________________.

Spherical Aberration (fuzzy image)

* Focal length will vary with part of lens being used
* Areas or zones of the lens that are closer to its periphery are stronger that have shorter focal lengths than zones near axis of the lens.

23

__________________refractive substances disperse light to some extent, hence lenses depart from ideal behavior.

Chromatic Aberrations

* Transparent materials do not refract all wavelengths equally.

24

________________variation of focal length with wavelength.

Longitudinal chromatic aberration

* Image will have out of focus color fringes at edge of objects.

25

_______________variation of magnification with wavelength.

Lateral Chromatic Aberration

* Size of an object imaged in blue light may be significantly different from the image formed in red light.

26

Not to be confused with spherical aberration, which is unlike ___________________, an image cannot be sharply focused for any part of the field no matter how much refocusing is done.

Curvature of Field
* Image defect produced by lens exhibits a moderate of curvature which may not be apparent visually.
* Only possible to get acceptable focus for only one area of the field of view (center, edge etc.)
* When attempt is made to photograph such image, difficulty of recording curved image surface on a flat film plane becomes apparent.

27

If the magnification is not constant across the field of view, the image will not be an exact representation of the object.

Distortion

28

______________is when magnification fall off, when moving from the center of the field toward periphery.

Barrel distortion

29

_______________when magnification increases toward the edge of the field.

Pin-cushion distortion

30

Magnification takes place in one stage, no more than a magnifying glass.

Simple microscope

Ex: hand lenses, fingerprint magnifiers

31

Magnification of a simple microscope:

M= least distance of vision + 1
focal length of lens

32

Magnification happens because the lens allows the image of the object to remain focus when the object is placed closer to the eye increasing the angle and resulting in larger image on the retina.

* Distance of closest vision for normal human eye is about 25 cm.

Simple microscope

33

Modern ______________have magnification in two stages.

Compound microscope (s)

34

_______________resembles a projector + magnifying glass.

Compound microscope

35

Last stage of the magnification in the ______________is essentially the same as in a _____________ ( a virtual image is formed) and it takes place in the eyepiece (ocular).

Compound microscope
Simple microscope

36

Ocular is used to examine a real image produced by the first image-forming lens system, the objective

* objective produces an enlarged real image of the object.

Compound microscope

37

Other factors for evaluating a microscope are:

Image quality
Visibility
Resolution

38

Compound microscopes have shorter focal length objectives characteristically have:

High powers

39

An increase in magnification that continues to reveal finer details in the object is called:

Useful magnification

40

Additional magnification that merely results in a larger image with no further detail is known as:

Empty magnification

41

Since in the compound microscope the image produced by the objective is magnified by the ocular, the approximate resultant overall magnification of the system can be found by multiplying the power of the __________by power of the ___________.

Objective
Ocular

42

For court purposes, common to use a calibrated scale known as ____________________, which is mounted on the microscope slide under the same conditions as specimen.

Stage micrometer

43

Two most common microscopes found in laboratories:

Biological microscope
Stereoscopic binocular microscope

44

Biological microscope:

Designed for use with transparent or translucent specimens and is earliest compound microscope.

45

Stereo microscope:

Most widely used instrument in the crime laboratory.

46

________________most basic form consists of 2 low to moderate power compound microscopes mounted side by side in a common housing so that the two are directed at the same area of the specimen from slightly different angles.

Stereo microscope

47

Most common type of illumination employed with the stereo microscope is variously termed:

Incident, reflected and vertical or epi

48

The______________of the stereo microscope is that microscopic objects tend to have very natural 3D appearances when viewed with the stereo microscope.

Main advantage

49

Most stereo microscopes have accessory for transmitted light illumination allows light to be directed through the _______________.

Sample from beneath

50

Consists of light directed onto the specimen from above and is suitable for use with opaque objects as well as certain transparent ones:

Stereo microscope

* incident, reflected and vertical or epi illumination

51

It is less the microscope than the lighting that provides the analysis with a stereo microscope.

True

52

Various wavelengths of light can provide luminescence or fluorescence in a sample.

True (Stereo microscope)

53

Levels of magnification 2.5X - 100X

Stereo microscope

54

The stereo microscope can be used for ____________or_____________testing.

Detection
Presumptive

55

Using a stereomicroscope on a _________________allows the microscope to be used on large objects.

Boom arm

56

Polarized Light Microscope:

Most versatile and powerful tool available for analyzing trace evidence.

57

________________ microscope is basically a biological microscope with several refinements and accessories added.

Polarized Light

58

The Polarized Light microscope is composed of a ______________and ____________crucial for optimal performance.

Lamp (illuminator)
Substage condenser

59

On a standard brightfield microscope, two___________filters are introduced into the light path; one between the sample and light source (polarizer) and one between sample and oculars (analyzer).

Polarizing

60

Stage on ___________rotates allowing the sample to rotate around the axis of the polarizer, providing responses to the polarized light.

Polarized Light Microscope (PLM)

61

Compound microscopes can be fitted with thermally controlled stages that can heat samples up to 350 degrees C.

Hot stage

62

Hot stage is:

Destructive analysis

63

Hot stage can help identify:

Materials, particularly polymers or to compare materials response to various temperatures.

64

Comparison microscope is:

Two carefully matched compound microscopes

65

In a comparison microscope, images produced by the two microscopes are____________in a common intermediate field plane within the ocular.

juxtaposed

* In this manner, 2 objects in two different fields of view can compared directly

66

The two types of comparison microscopes:

* One designed for opaque objects such as bullets, cartridge cases tool marks; uses incident illumination

* One for hair and fiber comparisons; transmitted light illumination

67

Transmitted light illumination is when:

The specimen is illuminated from the side opposite of the objective.

68

Often desirable to employ _______________and _____________methods simultaneously as well as sequentially when examining certain samples.

Transmitted light
Epi

69

For work with low or moderate power objectives, a crude ________illumination can be employed by simply directing a concentrated beam of light at the top of the specimen.

Epi

70

Ideal transmitted light illumination system should be capable of illuminating specimen _____________with adequate intensity.

Uniformly

71

Ideal transmitted light illumination system should allow __________of light paths so that only the area of the specimen being examined is illuminated.

Precise control

72

Ideal transmitted light illumination system should provide a __________and_________degree of whiteness or color temperature of the light.

Controlled
Predictable

73

Ideal transmitted light illumination system should be _____________to use without compromising precision.

Convenient

74

Ideal transmitted light illumination system has two primary components that supply illumination:

Illuminator
Substage condenser

75

_________________is the first component along the path of the microscope.

Illuminator

76

August Kohler devised special type of critical illumination called:

Kohler illumination

* For wide variety of applications

77

___________is the average operating voltage for high quality microscope illuminators.

6 volts

78

______________is brought to its operating temperature gradually, the life of the lamp will be greatly prolonged.

Lamp filament

79

__________microscope lamps should not be used at the full voltage unless doing so is necessary for brightness or color temperature considerations.

High quality

80

Rationale for use of low voltage lamps in high quality illuminators stems from the fact that for 2 filaments of equal wattage output, the one designed to operate at lower voltage can be made more___________.

Compact

81

The ideal _____________would produce a perfect cone of light with its apex at the specimen plane.

Condenser cone

82

The term _______________refers to a cone of light that does not exhibit effects of spherical aberration.

Aplanatic cone

83

Rays following non-prescribed paths manifest as_____________.

Stray light

84

______________is light that carries no information about the specimen; produces glare and reduction in image contrast.

Stray light

85

______________ produced is important because its form depends on how well the paths of light rays are controlled by the illuminator and condenser.

Character of the cone of light

86

Ideal condenser has two variables:

Angularity (angular aperture)
Size of the area of intersection

87

_____________of a condenser is controlled by substage or aperture diagram.

Angularity

88

Size of the area of an intersection from a condenser is:

- controlled by the lamp or field diagram
- area of intersection is the area illuminated
- area illuminated should be reduced with high power objective

89

Typical high power cone of a condenser has:

High angularity with small area of intersection

90

Typical low power cone of a condenser has:

Low angularity coupled with a large area of intersection

91

________________third optical component of the microscope.

The objective

* First and most critical image forming part

92

______________sets the upper limit for the image quality attainable by the microscope.

The objective

93

A poor __________can degrade image quality produced by the objective, but an excellent ________cannot compensate for a poor or improperly selected objective.

Ocular
Ocular