How to set up illumination for your microscope

To get the best image quality out of your microscope, it helps to know how to set up your microscope’s illumination system.

With a few small changes you can really improve resolution, contrast and sample visibility.

Light intensity

Managing intensity is a basic but important aspect of lighting.

Too high an intensity, and the image will be overexposed and hard to see. Too low, and the image will be too dark to make out the details.

You also need to adjust the intensity when you switch magnifications – the higher the magnification, the less light you’ll need.

Controlling the intensity is easy.

The light controls are usually on the base or side of your microscope, in the form of a dial or knob.

Adjusting the dial in one direction increases the light intensity. The other, decreases it.

In general, you want as much light intensity as you can get while ensuring it remains comfortable for your eyes. By doing so, you’ll see as much detail as possible.

Aperture diaphragm

Learning how to use the aperture diaphragm of your microscope can make a huge difference to image quality.

Controlled by a small lever on the side of your condenser, the aperture diaphragm determines your resolution, contrast and depth of field.

Moving the lever opens or closes a series of interlocking blades that form an opening (or ‘aperture’) that the light must pass through.

Narrowing the size of the aperture increases image contrast and depth of field, making your specimens easier to see.

Widening the aperture increases the resolution and brightness, allowing you to see more detail.

The downside is that you can’t have everything – to have more contrast, you must sacrifice resolution and vice versa.

Finding the right setting is therefore a balancing act that will depend on what type of sample you’re looking at and what you want to see.

A good starting point is to set the diaphragm to a range between 50% and 90%. This should give you a decent mix of detail and contrast.

Tip: If you want to specifically maximise resolution, you should match the aperture setting (the numbers under the lever) with the numerical aperture (NA) value of your objective lens. You can find this value written on the side of the lens.

Filters

Microscope filters can be a great way to get a better look at your samples.

These special tools slot into your illumination system and change the way the light looks, giving you more ways to see and study your samples.

The most common filters, such as daylight blue filters, adjust the colouration of the light. They’re often used to bring the yellow light of halogen or tungsten bulbs back to a more natural hue.

Filters can also enhance contrast, make certain stains more visible, and reduce chromatic aberration (where colours appear blurry or fringed around the edges).

They’re a popular choice with photographers. Apart from altering the colour, filters can soften the lighting or uniformly reduce the intensity as needed.

With the right illumination setup, you’ll be able to see your samples with greater clarity, contrast and colour. All it takes is a little know-how.