Forensic Microscopy Vocabulary Flashcards

Flashcards covering key terminology, principles, formulas, and components of microscopy in forensic science.

Simple Magnification System

A magnification system using a single lens to form an enlarged image of an object, with a practical limit of $10\times$ to $15\times$.

Compound Magnification System

A system consisting of two stages of magnification where total magnification is equal to the product of the magnification of the first and second lens.

Virtual Image

An enlarged image produced when an observer looks at a first image through a second magnifying lens.

Real Image

An image formed by an optical system that can be projected onto a screen.

Lens

A translucent material that bends light in a known and predictable manner.

Focal Length

The distance between two points of focus on either side of a lens.

Resolution

The minimum distance two objects can be separated and still be seen as two distinct objects.

Empty Magnification

Continued magnification of an image beyond the resolution limits of the lenses, which enlarges the image without improving its resolution.

Eyepiece (Ocular)

The lens that an observer looks into when viewing an object microscopically.

Monocular Microscope

A microscope equipped with only one eyepiece.

Binocular Microscope

A microscope equipped with two eyepieces.

Field of View

The total area visible when looking through the eyepieces of a microscope.

Objective Lens

The lens positioned closest to the object or specimen being studied, considered the most important part of a microscope.

Numerical Aperture

An angular measure of an objective lens' light-gathering ability and its resolving quality.

Tube Length

The distance from the lowest part of the objective lens to the upper edge of the eyepiece, standardized at $160\,m/m$.

Coverslips

Thin glass plates placed on top of mounted specimens to protect both the specimen and the objective lens from damage.

Stage

The platform where the specimen sits during viewing, which is moved to focus the specimen.

Condenser Lens

Lenses located below the stage that focus or condense light onto the specimen field of view to obtain a bright, even field of view and improve image resolution.

Condenser Diaphragm

A diaphragm used to eliminate excess light and adjust for contrast in the microscopic image.

Field Diaphragm

A diaphragm that allows more or less light into the lens system of the microscope.

Critical Illumination

Illumination method that concentrates light on the specimen with the condenser lens.

Köhler Illumination

Illumination method that sets the light rays parallel throughout the lens system, allowing them to evenly illuminate the specimen.

Refractive Index

The relative speed at which light moves through a material with respect to its speed in a vacuum, defined by $N = \frac{C}{v}$.

Snell's Law

The physical formula $N_1 \times \sin(\theta_1) = N_2 \times \sin(\theta_2)$ describing the relationship between angles of incidence and refraction for light passing between two media.

Isotropic Materials

Materials that demonstrate the same optical properties in all directions and have only one refractive index.

Anisotropic Materials

Materials whose optical properties vary with the orientation of incoming light and the optical structure of the material.

Polarizer

A special filter located beneath the stage with its preferred vibration direction set left-to-right to produce plane-polarized light.

Polarized Light

Light that vibrates only in one direction.

Analyzer

A polarizing filter located above the objectives aligned opposite of the polarizer that can manually be slid into or out of the light path.

Birefringence

The result of the division of light into at least two rays when it passes through certain types of material, calculated as $\Delta n = n_e - n_o$.

Retardation

The difference in velocity of the ordinary and extraordinary rays passing through a specimen, calculated as $R = t(n_2 - n_1)$.

Interference Colors

Colors diffracted when out-of-phase light waves strike the analyzer, caused by the destructive interference of light rays split by an anisotropic material.

Michel-Lévy Chart

A chart used in polarized light microscopy that gives diameter, birefringence, and retardation.

Fluorescence

The luminescence of a substance excited by radiation, where the wavelength of emitted light is longer than that of the exciting radiation.

Primary Filter (Excitation Filter)

A filter in fluorescence microscopy placed between the lamp and specimen to select short wavelengths of excitation light.

Secondary Filter (Suppression Filter)

A barrier filter placed between the specimen and eye that prevents excitation light from reaching the observer's eye while allowing fluorescence to be seen.

Transmission Electron Microscopy (TEM)

An electron microscopy technique where an electron beam passes through a very thinly sliced specimen and projects the beam onto a specially treated plate.

Scanning Electron Microscopy (SEM)

An electron microscopy technique where a beam of electrons rasters across a specimen to provide a non-colored image of its surface.