Introduction to Microscopy The Microscope

Introduction Microscope - an optical instrument consisting of a lens or several lenses used to view small items, which appear to be enlarged Magnification - the apparent enlargement of an object by an optical instrument Resolution - the process or capability of making distinguishable the individual parts of an object, closely adjacent optical images, or sources of light

Terminology Optical - of, relating to, or utilizing light especially instead of other forms of energy (as in optical microscopy) Lens - a piece of transparent material (such as glass) that has two opposite regular surfaces either both curved or one curved and the other plane and that is used either singly or combined in an optical instrument for forming an image by focusing rays of light

Terminology Eyepiece - the eyepiece (or ocular lens) is the lens that is closest to the eye – Types of eyepieces  Monocular - a microscope having only one eyepiece  Binocular - a microscope having two eyepieces

Magnifying Power Magnifying power - the magnification power is the product of the eyepiece lens magnification and the objective lens magnification (i.e. if the eyepiece lens has a magnification of 10x and the objective lens has a magnification of 10x, the magnifying power is 10x times 10x or 100x

Forensic Microscopy Forensic microscopy is used to identify and compare all types of physical evidence. Forensic microscopy applies equally to bullets, fingerprints, hair, fibers, footprints, soil, documents, tools, DNA, and handwriting.

Types of Microscopes Used in Forensic Comparisons Compound microscope - the most commonly used microscope A compound microscope works through the principle of light passing through two lenses to form a virtual image of the object seen by the eye.

Parts of a Microscope

Parts of the Compound Microscope Mechanical parts – Base - the support on which the instrument rests – Stage – the horizontal plate on which the slides of the specimens are placed – Arm – a c-shaped upright piece which acts as a handle for the microscope – Body tube – the hollow tube through which light passes between the objective and the eyepiece

Parts of a Compound Microscope Mechanical Parts – Adjustment knobs Coarse - the knob that helps focus the microscope by raising (or lowering) the body tube Fine - this knob allows the scientist to focus more precisely

Parts of a Compound Microscope Optical Parts – Illuminator- artificial light is often supplied by a light bulb to illuminate a specimen Transmitted illumination - the use of an artificial light source which is focused upward toward the sample – Objective lens - The objective lens forms an inverted initial image, which is subsequently magnified. This lens is found closest to the specimen. – Condenser - the condenser collects the light rays from the illuminator and focuses them on the sample – Eyepiece - the lens closest to the eye

Stereo Microscope A microscope that produces a three-dimensional image of an object by focusing on the object from slightly different positions in each of two lenses. The image formed by a compound microscope is inverted, but the image formed by a stereoscopic microscope is right-side-up.