Glossary of Microscope Terms

Abbe Condenser: Consists of a lens and an adjustable iris and is mounted below the stage The iris controls the amount of light passing through the specimen. The focal point of the light emerging from the lens is controlled by adjusting the vertical position of the lens using a rack and pinion control.

Achromatic Lens: Prevents colour separation when light passes through a microscope lens. As light frequencies have different refractive indices colour separation will occur when light passes through a lens. By using glass with varying indices of refraction, achromatic lenses can reduce the degree of colour separation. See also plan and semi-plan objectives.

Binocular Microscope: Has two eyepieces. Essentially the same structure as a compound monocular microscope with two eyepieces replacing the single eyepiece of the monocular microscope. (See also stereo, or dissection microscope).

Coaxial Focus: Uses a course and a fine focus knob on a single axis to bring a specimen into focus. The focus is normally achieved by moving the microscope stage below the objective lens.

Compound Microscope: Monocular, or binocular microscopes that have a number of objective lenses to produce a range of magnifications. These microscopes transmit light through a prepared slide. Also see stereo microscopes

Dissection Microscope: See stereo microscopes.

Eyepiece: In a compound and stereo microscope the eyepiece is the lens through which you view. It is also called an ocular lens.

Oil Immersion Lens: Oil immersion is used with the 100 x objective of a compound light microscope. Light is refracted when it passes through one medium into another with a different refractive index, (for example air to glass). This results in a loss of definition of the image. Immersion oil has the same refractive index as glass. Therefore there is no refraction of light when it passes from glass to oil and from oil to glass. By placing a drop of immersion oil on a slide, and immersing the 100x oil immersion objective directly into the drop we reduce refraction between the specimen and the objective and so preserve clarity of the image.

Magnification: An optical compound microscope magnifies a specimen by using an objective lens and an ocular lens (eyepiece). The total magnification is the product of the eyepiece magnification and the ocular magnification, for example, an objective with a magnification of 100X and an eyepiece with a magnification of 10X will give a combined magnification of 1000X.

Monocular Microscope: A compound microscope with a single eyepiece.

Objective Lens: This lens sits just above the specimen and focuses the light for the ocular (eyepiece). Objective lenses typically magnify the image 4X, 10X, 40X, and 100X.

Parfocal: A parfocal microscope allows the objectives to be rotated on their turret without losing focus. In practice you will still need to adjust the focus with the fine focus control.

Plan and Semi Plan Objectives: Normal lenses split white light into its constituent colours and distort the image at the edges. Plan lenses are designed to eliminate distortion and produce a clear image across the full field of view.

Stereo Microscopes (dissection microscopes): are used to examine “large” specimens such as insects, fossils, flowers, plants etc. Stereo microscopes use two objectives and two eyepieces to give separate views of the specimen creating a three dimensional view of the object. Unlike compound microscopes the two objectives sit at a distance from the specimen allowing it to be manipulated, or dissected while viewed through the microscope. Unlike compound microscopes their magnification is low, typically up to 80X. Illumination is from above the object, although many stereo microscope also illuminate from below the object.