Lecture 2 Jan 29 2018 Flashcards
(93 cards)
1
Q
The term microscopy used to describe:
A
Analytical approach in which a microscope plays a central role in maximizing extraction of useful information from a variety of samples.
2
Q
Identification (ID) of general unknown is greatly facilitated with a______________________.
A
Preliminary Microscopical Examination
3
Q
Applications of the microscope in forensics include:
A
- Document examination
- Tool mark comparison
- Firearms ID
- Serology
- Drug chemistry
- Trace evidence
4
Q
Microscope used as a symbol of science but seems less exotic than recent instrumentation, in some cases____________________.
A
old fashioned
5
Q
________________and______________are the two main purposes of a microscope too create an enlarged image of an object that is clear and distinct.
A
Magnification
Resolution
6
Q
Magnification and resolution conflict with each other:
A
As magnification increases, resolution can decrease
7
Q
Greater resolution means greater detail, while greater magnification means ________________.
A
Larger image
8
Q
A converging (also known as positive )lens can form images in two ways:
A
Real image
Virtual image
9
Q
____________ 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
A
Real image
10
Q
_____________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
A
Virtual image
11
Q
___________________ distance from the lens to the principle focus (for thin lens).
A
Focal length
12
Q
If an object placed at infinity, the image will form at:
A
Principle focus
13
Q
If object placed at principle focus, image will form at _____________.
A
Infinity
14
Q
_________ of a simple lens is defined by a straight line running through the centers of curvatures of the two surfaces.
A
Axis
15
Q
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:
A
Principle focus of the lens
16
Q
_____________(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.
A
Equivalent focal length
17
Q
Magnification (M) for a real image can be defined by the equation:
A
M = Q/P
18
Q
If, P=2F=Q, magnification is:
A
1
19
Q
If P>Q, then M<1 :
A
Means there is a reduction
20
Q
If P1:
A
We have conditions for magnification by microscope objective
21
Q
__________________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
A
Aberrations
22
Q
The variation of focal length with distance from the lens axis is called__________________.
A
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
Q
__________________refractive substances disperse light to some extent, hence lenses depart from ideal behavior.
A
Chromatic Aberrations
- Transparent materials do not refract all wavelengths equally.
24
Q
________________variation of focal length with wavelength.
A
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
