What is a Compound Microscope?
This is the most common type of microscope, found in any school or microbiology lab. It's used to greatly magnify tiny specimens like amoebas or thin sections of specimens like leaves or muscle tissue mounted on microscope slides. A compound microscope is ideal for observing cells and cell structure. Almost every student will use a 400x (400-times magnification) compound microscope to study biology. What is a Stereo Microscope?
These have lower magnifications of 15 to 45x, and are designed for viewing whole, three-dimensional objects like rocks, insects, flowers, and dissection specimens. They are important for advanced nature studies and ideal for children since an object can be viewed without preparing a slide - simply stick it under the microscope.
Terms and Parts of a Compound Microscope
This list explains the main parts of your compound microscope and the function of each. See these parts on the microscope diagram shown below the glossary.
Condenser: The light rays from the microscope's illuminator (light) are condensed and focused through this lens in the center of the microscope stage, providing better image resolution. Most 1000x scopes have a built-in, movable 1.25 Abbe condenser underneath the stage.
Disc diaphragm or Iris diaphragm: The disc diaphragm is used on most microscopes without 1000x. It's a rotating disc fixed under the stage, designed to provide the best resolution for the objective lens. Turn the disc to the smaller holes when using low magnification (40x to 100x) and to the larger holes for high magnification (400x). Most 1000x models have a fully-adjustable iris diaphragm with an easy, sliding control lever rather than a rotating disc. This type of diaphragm allows you greater control of contrast and helps achieve high image resolution.
Eyepiece: The part of the microscope that you look through. Eyepieces in most compound microscopes have a lens with a 10x magnification level (although you can upgrade with a 15x eyepiece). The National Optical 131 microscope has a pointer built in, which appears as a black line across half of the field of view. To move the pointer, just turn the top of the eyepiece.
Field of view: This is the area that's visible when you look through the eyepiece. The greater the magnification used, the smaller the field of view (i.e., FOV at 40x is much greater than at 1000x. This is why you should locate a specimen at lowest power and then gradually narrow your focus as you are increasing magnification).
Filter holder and filters: Some microscopes (like our Home 1000x) come with a swing-out filter holder at the bottom of the condenser. Blue and yellow filters can be used to enhance the image in some situations.
Focusing: Turning the focus knob or knobs moves the microscope stage up and down to bring the slide sharply into view. Most microscopes have both fine and coarse focusing, either as two separate knobs or else coaxial (one on top of the other for easy reach).
Head: The standard head type is monocular - just one eyepiece. Some microscopes will have a dual head so a teacher and student can view a slide at the same time (it's also convenient for video/digital photography with a digital microscope camera). The most deluxe models have binocular heads for extra-comfortable viewing.
Illumination: There are several types of electric lighting for microscopes:
- Tungsten is the least expensive illumination. It is hotter and less bright than the other kinds.
- Fluorescent illumination provides cooler and brighter light than tungsten. This is beneficial when viewing slides for long periods of time or observing live specimens, such as protozoa.
- LED is a bright cool source of light with a bulb that is much longer lasting than a fluorescent bulb. Microscopes with LED lighting typically have a variable control allowing you to change the intensity of light.
- Halogen provides the very brightest illumination. The best microscopes have halogen lighting and most stereo microscopes with top lighting also use halogen lighting. The intensity of halogen light can be adjusted with a variable control.
Lenses: Standard achromatic lenses help prevent color distortion. Semi-plan or plan lenses improve image quality through superior clarity and flatness. Super high contrast lenses offer extra image contrast so that the image appears much sharper.
Magnification: Multiply the magnification of the eyepiece by the magnification the objective lens for the total magnification at that power. If you have a 10x eyepiece and are looking through the 4x objective, the specimen you see is magnified 40x its actual size. Magnification of 400x or 1000x is necessary for studying cells and cell structure.
Mechanical stage: This fits onto the stage (in some microscopes it is built in) and provides the best slide control, which makes viewing easier. Clip the slide into place and use the X and Y-axis knobs on the stage to move the slide back and forth under the objective lens.
Objective lens: This is second lens of the microscope after the eyepiece. Compound microscopes have a 'nosepiece' with a rotating objective turret, which allows you to change the magnification level for different specimens. The standard objectives are 4x, 10x, and 40x for total magnification of 40x, 100x, and 400x. DIN is an international standard of lens quality.
Oil-immersion objective: Some microscopes have a fourth objective, a 100x oil-immersion lens for 1000x magnification. This allows you to see greater cell detail and cell structure. To use this lens, you need to put 1-2 drops of immersion oil on the slide coverslip. Immersion oil prevents light distortion, so that you can see a sharp image even with the lens pressed right up against the slide.
Parcentered: This means that if you centered your slide while using one objective lens, it should still be centered even when you switch to another objective.
Parfocal: This means that once you've focused on an object using one objective, the microscope will still be coarsely focused when you switch to a different objective. All you'll have to do is adjust the fine focus a bit.
Stage: This is the platform that holds the slide up beneath the objective lens. The stage clips hold the slide in place. (In some microscopes, these are replaced by a more convenient mechanical stage).
Stage stop:This is the small bar and screw between the stage and the arm of the microscope. It prevents the stage from coming too far up, so that the stage can't grind against the objective lens. This is also known as a 'safety rack stop,' and is pre-adjusted by the manufacturer although it can be adjusted by you if need be.
Diagram of Compound Microscope Parts
Terms and Parts of Stereo Microscopes
The following list explains the basic stereo and dissecting microscope parts and functions of each part.
Stereo head: Most low-power microscopes have what is called a stereo head, which has two eyepieces - looking through them is something like looking through a pair of binoculars. Some stereo microscopes only have a monocular (single) eyepiece.
Eyepiece: This is the part of the microscope that you look through. Eyepieces in stereo microscopes typically have a lens with a 10x magnification level. (You can increase power with a 20x eyepiece upgrade, though.) Both eyepieces have the same magnification on stereo head microscopes.
Diopter: In binocular eyepieces, this compensates for focusing differences between your eyes so you see the image clearly through both eyepieces.
Objective lens: The objective lens together with the lens of the eyepiece make up the microscope's magnification. Some stereo microscopes have a rotating objective turret (such as the one pictured below), which allows you to change the magnification level for different specimens; others have a set objective. Stereo microscopes actually have two separate objectives so that each eye is looking through an eyepiece lens as well as an objective lens.
Focus knob: Moves the head of the microscope up and down to bring the object sharply into view. Most stereo microscopes have only one focus knob.
Lighting: Top lighting shines down and reflects off opaque or solid specimens; bottom lighting shines up through transparent objects. The microscope pictured below has top and bottom lighting, though not all microscopes will have both.
Rack and pinion focusing: Most stereo and dissecting microscopes have standard 'rack and pinion' focusing. Turn the focus knob to slide the head of the microscope up and down (closer or farther from the specimen).
Stage clips: These hold microscope slides (which can be viewed under a stereo microscope as long as you don't need to see fine cell details) or other thin objects in place on the stage.
Stage plate: Where the specimen is placed for viewing; located directly under the objective lens. Some stereo microscopes have reversible black and white stage plates to provide appropriate contrast with the object being viewed. (Black for light-colored or see-through specimens and white for darker or opaque specimens.)
Diagram of Stereo and Dissecting Microscope Parts
The diagram below shows where each part is located on a typical stereo microscope.