What are the parts of a microscope?

Prepare, Light, Setup, Focus and Zoom. Five basic steps to get you jump started to becoming a microscope pro in no time. Once you have your specimen, and your light ready to go, you just setup your microscope and get focused. You can then iteratively increase the zoom power and get up close to your sample, and see the whole microscopic world!

Basic Parts

Any microscope from pocket microscopes to laboratory compound microscopes all have thee basic four parts: eyepiece, objective, light source and focus knob.

Eyepiece: The eyepiece lens on a microscope is the part of the optical system near where you place your eye to view the magnified object. In something like a pocket microscope, the eyepiece may not be adjustable or removable in any way, but in compound microscopes you can replace and upgrade them as you wish. There is so much to know about eyepieces we made a separate article on that topic called “Everything about Microscope Eyepieces”.

Objective: The objective lens on a microscope is part of the optical system that is responsible for producing a magnified image of the specimen being viewed. It is the lens closest to the specimen and is positioned at the bottom of the microscope’s nosepiece. There is a lot to talk about when it comes to objectives so we have a whole post dedicated to just that called “Everything about Microscope Objectives”.


Light Source / Illumination: Any microscope needs a light so you can see your object. This applies to a digital microscope to a pocket microscope to a compound microscope. There is different types of illumination sources, such as LED light microscopes to fluorescent microscope sources. In a pocket microscope, this can be as simple as a single LED, whereas expensive light sources can require a whole separate light generator.

biology scientist using compound microscope focus knob to illuminate specimen in high resolution, microscope condenser light source

Focus Knob: Except for some fixed power pocket microscopes that have a preset and fixed focus, every light microscope has a focus knob. The focus knob allows you to adjust the focus as you change magnification and zoom, or to adjust focus between different users with different eyes. What does the coarse adjustment knob do on a microscope? It makes large adjustments to the focus.


The drawtube is the optical tube on the microscope that holds the eyepiece and along where the light travels from the objective lens. Inside the drawtube is the path of light that goes from the objective to the eyepiece lens. This important tube is located between the main body of the microscope and the eyepiece and is usually made of metal or plastic.

There are standard diameters and lengths for these tubes. For the lengths, the German standard DIN is 160 mm and the Japanese standard JIS is 170 mm. Each objective states which tube length standard is used to calculate the magnification. If you use an objective lens with the wrong standard of tube, that magnification will be wrong.

Microscope Stage

The stage is the platform where you place your specimen or slide. Any stage consists of two parts: the stage platform and the slide holder. The stage platform is a flat surface that supports the slide, while the slide holder holds the slide securely in place.

What is a mechanical stage?


The mechanical stage of a microscope is a platform that holds the slide containing the specimen being observed. Since its mechanical versus a basic staged, it also allows for precise movement of the slide in the two primary directions (known as the X and Y directions), enabling the user to scan the specimen precisely even when viewing different areas at high magnification.

The mechanical stage is an important component of a microscope because it allows for accurate positioning of the specimen and makes it easier to locate and observe specific features of the specimen. Without a mechanical stage, it would be much more difficult to observe and study small or complex structures under a microscope.

What are the parts of a mechanical stage?

microscope parts of mechanical stage on microscope, microscope slide holder slide clip, microscope stage lock, stage control knobs

Slide Holder: This is where the slide sits and is retained.

Slide Clip: Rotate the slide clips out of the way when inserting the slide, and release when the slide is in position.

X Y Control Knobs: These knobs move the slide in the X and Y directions, and is necessary for fine positioning control at high powers.

Stage Lock: Don’t want to lose your spot? Lock the stage down with this tightening screw.

Stage Opening: This hole allows the light to pass up from the condenser lens through the specimen.

Graduated Locator Markings: This is a special ruler that allows you to measure movements and positions on the stage or slide. Review the next question if you need to know how to use it.

How do I measure using a mechanical stage?

When measuring on a mechanical stage, you want to check the position of the X and Y scales. Use the steps below for using and measuring on a Vernier scale to get the measurements for each axis. If you move the stage by turning the mechanical stage knobs, you can then take the new position measurement again. If you subtract the difference, you know exactly how far you moved on the physical specimen. So if you center the left side of an object, then measure, and then center the right side of an object and measure, the difference is the width of that object.

How do I measure using a Vernier scale?

To use a Vernier scale, you have to take the measurement off the main scale, and then look at the spot where the two scales, the main scale and the Vernier scale line up. The line where that happens is the additional measurement. In the photo example, the main measurement is the 2 from the 20 mm measurement. The 0 on the Vernier scale doesn’t pass the first line, so the measurement is 20 mm, not 21 mm. If it was past the first line, then the base measurement would be 21 mm, or past the second line would be 22 mm and so on. For the next decimal place, the Vernier scale lines up at the third line, so 0.3 mm, so the total measurement is 20.3 mm.

Condenser Lens

The condenser on a microscope is an optical component that is located below the stage and is used to focus and direct light onto the specimen being observed. Its primary function is to gather and concentrate light from the microscope’s light source (such as an LED or halogen bulb) and direct it through the specimen.

The condenser contains a lens system that helps to focus the light into a tight cone, which is then directed towards the specimen. By adjusting the position of the condenser, the angle and intensity of the light can be controlled, allowing the user to optimize the illumination of the sample.

In addition to focusing the light, the condenser also helps to control the amount of light that reaches the objective lens. By adjusting the aperture diaphragm located in the condenser, the user can adjust the numerical aperture of the system, which affects the resolution and depth of field of the microscope image.

Overall, the condenser is an important component of the microscope that plays a key role in producing high-quality, well-illuminated images of the specimen being observed.

Iris Diaphragm

The iris or iris diaphragm is usually one of the most forgotten about but powerful parts of a compound microscope. It can control your illumination and optimization of the iris allows you to achieve crisp, higher contrast images than you would without adjusting this part.

microscope iris diaphragm, compound microscope iris to control light illumination for high contrast imaging view with clarity

When you are first setting up your microscope you can start with the iris fully opened. But once focused, you can also try adjusting the iris. Usually the ideal position is around 70-80% but see what works best for your sample. Play with the combination of focus, light intensity and iris position until your object’s edges really pop.


Filters are an optional part of a microscope but can help you see certain details better, and the filter you want to choose depends on the sample you are viewing. Most filters are some form of a color filter, so specific wavelengths of light are filtered out and others pass through. As certain parts of a specimen, such as the nucleus in a cell, may show more contrast with a certain filter than the rest of the cell.

What are the different types of filter mounts on microscopes?

Filter Wheel: Some microscope have pre-installed filter wheels, where there is a turret of options. There is one spot that is empty so you can view without any color filters, but you can rotate through them and try various filters with your sample to see which works best.

Filter Holder: Most compound microscope just have a single filter holder, and the size may vary. Check which diameter your filter holder is and then you can purchase any other ones of the same size.

How do I install a filter on a microscope?

Filter holders on a microscope are typically under the condenser lens, and may or may not have a handle to rotate them. Without a handle sometimes makes it easy to miss, so check carefully for where your filter holder is located, and once you find it rotate it out gently. Insert your filter into the round tray holder, and then rotate fully back into place.

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