Understanding the mechanical stage of a microscope

The mechanical stage is a vital yet unappreciated component of any microscope.

Sitting below the objective lenses, it’s the stage (or platform) upon which your slides and samples sit.

It both keeps your slides steady and allows you to move those slides with smooth precision.

Here’s a quick overview of the humble mechanical stage. 

What is a microscope stage? 

A microscope stage is a flat surface that sits below the objective lenses and above the light source.

The stage has a hole in the centre that allows the light to pass through, and you position your slides over that hole in order to illuminate your samples.

Stages, both simple (non-mechanical) and mechanical, typically have some form of slide holder. Whether a spring-loaded holder or in the form of specimen clips, they serve to keep your slides stable, so your samples aren’t easily knocked out of focus.

What does a mechanical stage do?

With simple stages, the stage doesn’t move at all. In order to see a different area of your slide, you have to physically reposition the slide on the stage with your hands.

This is not only inconvenient, but it makes it very easy to accidentally knock your slide out of focus. It’s also quite difficult to methodically scan over a sample using this approach or to keep track of a living specimen.

A mechanical stage on the other hand can be moved. Using the attached controls, a mechanical stage can be smoothly moved left, right, back and forth.

This allows you to easily observe any section of a slide, while ensuring that it stays in perfect focus. You’re also able to keep looking down your eyepieces while you scroll, as there’s no need to worry about handling the slides.

How does it work?

Using a mechanical stage is straightforward.

The controls will generally be found at the rear right of the mechanical stage, as an accommodation to right-handed microscope users. Stages with the controls on the left side are, of course, also available.

Generally, there’s a vertical pole hanging underneath the stage with two knobs at the end. One knob controls the left-right movement while the other controls the back and forth movement.

Simply rotating either knob will move the stage in the desired direction, although it may be a little unintuitive at first due to the orientation of the knobs.

The controls are designed to provide as smooth a motion as possible, allowing you to stay focused on the task at hand without the need to adjust either the slide or the focus.

Many stages also come with graduated markers along either axis, allowing you to note down the position of any areas of interest in a sample so that you can easily return to them later. 

Specialist mechanical stage

While the standard mechanical stage described above is by far the most common model, you may run into more niche mechanical stages, such as the circular stage and the universal stage.

Circular or rotary

Circular mechanical stages allow you to rotate your samples a full 360 degrees. They allow for a much more flexible point of view, making them useful for both standard microscopy as well as photomicrography (photography using a microscope).

Universal

Resembling the armillary spheres used by ancient astronomers, universal stages are comprised of a series of concentric rings that allow a sample to be rotated and tilted on several axes.

Universal stages are quite rare and are generally used to observe birefringence in geological samples.