Microscope Parts Glossary

In order to evaluate microscopes and determine what kind is best for your requirements, you'll need to know some basic microscope anatomy terms.

Arm
The microscope arm connects the body tube to the base. Functional and heavy, it's a stabilizing piece that supports the body, stage, and eyepieces.

Base The heavy, supportive piece at the bottom of a microscope. The base is typically shaped to accommodate a light source for viewing slides and specimens. Coarse Focus Knob A microscope's coarse focus knob quickly moves the objective lens on both high-powered and low-powered microscopes either toward or away from the specimen. Coarse focus knobs function via a rack and pinion system. Care should be taken when coarse focusing that the objective doesn't touch the specimen and cause damage. A safety rack stop (see below) can guard against this.

Eyepiece
Microscope eyepieces are the top lenses through which a focused image is viewed. Most eyepieces magnify the image at a power of 10x, but the magnification range of lenses may vary from 5x to 20x. Though various microscope eyepiece designs are available, the differences between them are minor in comparison to the great variety and differing effect of telescope lenses.

Eyepiece Tube
The eyepiece tube or body tube is the barrel that houses the eyepiece through which the image is viewed. It's best to avoid eyepieces and objectives with plastic optics due to their overall low quality.

Fine Focus Knob
With high-powered microscopes, the fine focus knob is used to fine-tune an image after the coarse focus knob has been properly adjusted. Adjusting a fine focus knob causes the objective lens or microscope stage to move along a rack and pinion. This movement is small in comparison with coarse focusing, and thus there's little danger of crushing the objective against the specimen when fine focusing.

Illumination Mirror
A microscope features either an under-stage light source (tungsten, fluorescent, or halogen) or an illumination mirror that reflects an external light source through the bottom of the microscope stage. When using an illumination mirror, its concave side should be used for higher magnifications or brighter light, and its adjustable flat side for obtaining a better image.

Nosepiece
Microscope nosepieces usually hold two or more objective lenses and can be rotated or revolved for fast, simple changes in magnification. The nosepiece is also known as a turret if it holds multiple lenses.

Objective Lens
The objective is the lens that's closest to the specimen. Most microscopes feature a variety of objective lenses, which allows the viewer to choose from different magnifications. A microscope's total magnification is determined by multiplying the eyepiece magnification by the objective lens magnification. The highest-quality lenses are made of glass; plastic lenses should be avoided, even by beginners.

Safety Rack Stop
The safety rack stop (see the Coarse Focus Knob definition) is a device which prevents the pinion from rolling along the rack and causing the objective to collide with the specimen. Setting the safety rack stop properly is essential to preventing damage to your microscope.

Specimen Stage
The specimen stage is the platform on which a slide or specimen is positioned for viewing. Beneath the stage is a light source or illumination mirror, and above it is the objective lens.

Stage Holder Clamp
Stage holder clamps hold specimen or microscope slides in place. Without them, even a slight movement could prevent you from viewing a specimen because of how magnification affects the image.