Microscopy in Forensic Science - Chapter 8 The Microscope

Flashcards covering microscope basics, components, and advanced forensic microscopy techniques from Chapter 8.

What is a microscope?

An optical instrument that uses lenses to magnify and resolve the fine details of an object.

What is a virtual image?

The magnified image seen by looking through a lens.

What is a real image?

An image that is viewed directly (formed by the lens system).

In a basic compound microscope, where is the object placed and through what is it viewed?

The object is placed under the objective lens and viewed through the eyepiece.

How is the magnification of a compound microscope calculated?

Multiply the magnifying power of the objective lens by the magnifying power of the eyepiece lens.

What are the two main systems of a microscope?

The mechanical system and the optical system.

Name three components of the mechanical system.

Base, arm, and stage (the supporting structure of the microscope).

What is the function of the coarse adjustment knob?

To bring specimens into approximate focus by moving the body tube.

What is the function of the fine adjustment knob?

To fine-tune focus by moving the body tube a small amount.

What is the illuminator in a microscope?

An artificial light source used to illuminate the specimen.

What is transmitted illumination?

Light directed up through the specimen from the base.

What is vertical (reflected) illumination?

Light that comes from above and reflects off the specimen.

What is a condenser?

A lens system under the microscope stage that focuses light onto the specimen.

What is the objective lens?

The lens closest to the specimen; usually several objectives are mounted on a revolving nosepiece.

What does parafocal mean?

When the microscope is focused with one objective, another can be rotated into place and the specimen remains very nearly in correct focus.

What is the eyepiece or ocular lens?

The lens closest to the eye; can be monocular or binocular.

What is the difference between monocular and binocular microscopes?

Monocular has one eyepiece; binocular has two.

What is a comparison microscope?

Two independent objective lenses joined by an optical bridge to a common eyepiece; allows side-by-side viewing of objects.

Why is the comparison microscope important in firearms examination?

It provides a side-by-side magnified view of bullets for comparison.

What is a stereoscopic microscope?

Two aligned monocular microscopes that produce a 3D image; magnification roughly 10x–125x; has a large working distance.

What is polarizing microscopy?

Microscopy using plane-polarized light to study materials, especially birefringent substances.

What is birefringence?

A property of materials that split a beam of light into two rays with different refractive indices; helps identify minerals or fibers.

What is a microspectrophotometer?

A spectrophotometer coupled with a light microscope that can obtain visible absorption or IR spectra of the observed material; useful for trace evidence.

What magnification range does a scanning electron microscope (SEM) offer?

From about 100x up to about 100,000x (with very high magnifications possible under certain conditions).

What additional information does SEM provide besides images?

X-ray emissions that can be used to characterize elements present in the material (EDS/EDX).

Which elements are commonly detected in gunshot residue with SEM/EDS?

Lead (Pb), Antimony (Sb), and Barium (Ba).

How can SEM help in primer residue analysis on hands?

It measures Ba and Sb on relevant hand areas and analyzes particle morphology to determine firing or handling of a weapon.

What is forensic palynology?

The collection and examination of pollen and spores connected with crime scenes, illegal activities, or terrorism; the microscope is the principal tool.

What are some uses of pollen/spore evidence in forensic palynology?

Link a suspect or object to the crime scene or victim; prove/disprove alibi; include/exclude suspects; track whereabouts; indicate geographical origin.