What Is A Microscope Condenser And Why Do They Matter?

Microscopes are one of the most important and vital tools used by scientists and researchers.

The multiple compartments and stages that make up a microscope allow us to view specimens incredibly small in stature including cellular structures of organs, germs and bacteria that are invisible to the naked eye.

What Is A Microscope Condenser And Why Do They Matter?

The condenser is one of the most integral components of a microscope that allows us to even get a clear view of what we have placed on the illuminator, and without it a microscope would fail to function at all.

Condensers are incredibly important for analyzing specimens and therefore should always be taken into consideration as there can be many different kinds that can give us different results when used.

To make this clearer, we have taken a deep dive into what exactly are microscope condensers, and why they matter at all.

What Is A Microscope Condenser?

The condenser on a microscope is located right under the stage and hovers above the illuminator.

It works by focusing a light which passes through the stage of the microscope where the specimen is mounted providing a clear and illuminated view.

When we are using a light source to illuminate a specimen in a microscope, the rays of light will be scattered and aimed in different directions and when this might pass through the microscope slide and into the lens it looks unorganized and messy since the light can’t direct itself onto one surface.

This is where a condenser comes in, it works to ‘converge’ all the light rays into one focused lens centered on the specimen creating a much more clearer and vivid picture of what we want to analyze.

They were first introduced on pre-achromatic microscopes in the 17th century, however by the 19th century scientists such as Benjamin Martin and Joseph Jackson Lister began understanding the huge benefits of condensing the area of the light source and directing it to the area of the actual specimen they are analyzing.

By the late 19th century, condensers had become far more refined and efficient with their popularity spreading all across Europe.

The condenser itself is made up of one lens or a set of lenses, and the intensity of the light it produces can be adjusted by moving the condenser closer or further away from the stage depending on how clear you want the image.

Even the width of the beam can be adjusted by making the aperture wider or smaller.

Most researchers will set the condenser on a wide aperture, and have it as close to the stage as possible as this will often always produce clear results.

Why Is A Microscope Condenser So Important?

As new microscopes are developed and as you use higher magnification levels, condensers become ever more important and are vital to use and update in order to utilize each microscope to its full efficiency.

They are also incredibly important because the whole purpose of a condenser is to direct the light that passes through the specimen and into the microscope’s objective.

If a microscope were not to have a condenser, the quality of the image would be much more unclear to the point where analyzing exact movements and shapes would be near impossible.

It is the condenser specifically that illuminates specimen samples from beneath, shining light through it and into the objective lens for viewing.

The condenser does this job in conjunction with an iris diaphragm sitting between the condenser and the underside of the sample which is also adjustable.

As mentioned previously, without a tool to converge and direct the rays of light, the light source would be scattered around the scope and would only make the specimen image blurry and foggy rather than focused and clear.

Different Types Of Microscope Condensers

Different Types Of Microscope Condensers

There are four primary types of microscope condensers each with their own specific functions and purpose.

All of these condensers are often readily available to buy and while the Abbe Condenser is often the most common and popular, you will still be able to purchase the others and it is well worth considering them if you never have as they can enhance your analytical results by quite a large margin.

Here are each of the four common types of condensers along with how they function and what they are best at.

Abbe Condenser

The most common type of condenser and first created by Ernst Abbe in the 19th century, most microscopes will already be fitted with a 1.25 NA Abbe condenser because of how widely used and common they are.

An Abbe condenser can consist of one to three lenses which provide a combined numerical aperture range of up to 1.3 which makes it one of the better options for medium to high magnification objectives.

Abbe condensers are known for being cheap and produced in masse but still effective, however they can come with some drawbacks that can make them a bit less efficient than other condensers if you want the clearest image possible.

For one, an Abbe condenser will not accommodate for any spherical lens aberration or chromatic lens aberration.

This is when the edges of a curved lens fail to direct light rays to the same focal point as the rest of the lens, creating a blurry image which can be hard to get around even by adjusting the condenser itself.

This can also create ‘color fringing’ where all the colors are not focused on the same focal point and instead appear around the edges of the object rather than on the object itself.

Abbe condensers are great for beginners or if you want to analyze a specimen with a magnification level below 400x, however for anything higher than this it can be a good idea to opt for another condenser.

Aplanatic Condenser

Some of the issues present in the Abbe condenser including spherical lens aberration are resolved by the Aplanatic condenser.

These condensers are able to correct the spherical aberration that can occur from the surface of a lens being spherical in shape which makes it near impossible to make a perfect lens.

If you find you really need perfect light to analyze a specimen and need to avoid the blurry images caused by spherical lens aberration, then more advanced condensers such as these are far more optimal.

Aplanatic condensers are the perfect workaround for this, however one area they do fall short in is chromatic lens aberration which they can be less resistant against.

This is where you can get ‘color fringing’ with all colors being directed in separate directions and not being focused on the objective.

Aplanatic condensers are still very effective and work well at flattening out light rays and directing them towards one area to avoid lens aberration, however they are much less resistant to color fringing.

Achromatic Condenser

Achromatic condensers fill in the problems that are left by the aplanatic, specifically the issue of color fringing or chromatic lens aberration.

The way a Achromatic condenser does this is by condensing all light waves across the color spectrum to ensure they all meet at one focal point.

They are a more advanced type of condenser that can be great for researchers to get the most accurate and clear images possible, but they are also the preferred condenser for those who do photomicrography and photograph their findings for experimental purposes.

There is a catch however, while great for directing light rays they can succumb to the issue of spherical aberration, so they are more suited if it is specifically colors you want to direct onto the specimen rather than a guaranteed crystal clear image.

Aplanatic-Achromatic Condenser

By far the most expensive type of condenser, the Aplanatic-chromatic condenser essentially works by mitigating the issues plaguing the previous two.

This includes being very resistant to both spherical and chromatic lens aberration.

Because it can adjust for both types of aberration, this is an extremely popular option among photomicroscopists and very high level scientists.

While it may seem all positive, there are even some slight drawbacks to this condenser too.

For example, depending on the specimen being analyzed they might require a lower powered and broader light cone while others can require very narrow light cones for higher powers objectives, so one condenser cannot always be the perfect solution to trump all others, each has their own benefits and drawbacks.

Numerical Aperture

Condensers vary in their numerical aperture, however it is incredibly important since it dictates the optical resolution.

The rule of thumb for the best results is that the numerical aperture of a condenser has to be matched with the numerical aperture of the objective.

Therefore if your objective is found to have a numerical aperture of 0.80, then the condenser setting should also be set to that number in order for the resolution to be the best it can be.

Condenser lenses with a maximum numerical aperture that is greater than 0.95 are usually designed to be used under oil immersion or even water immersion in very rare cases.

Oil immersion is often used to actually improve the overall numerical aperture and the resolution overall.

If you find the condenser has a numerical aperture setting lower than 0.95 then it is not likely supposed to be used with oil or other fluids on top of the lens and are deemed ‘dry condensers’.

A dedicated dry condenser will focus light much more precisely than a dry/immersion condenser.

In order to adjust the aperture diaphragm to match the numerical aperture of the objective, the user must turn the knurled knob or lever usually found to the side.

There is often a small yellow or white dot index located on the condenser that is used to indicate the relative size of the aperture.

In fact, many manufacturers will synchronize the gradation to automatically correspond to the approximate numerical aperture of the condenser.

For example, if the microscopist has selected a 10x objective of numerical aperture 0.25, then the arrow would usually be next to the value of 0.20 to 0.25 as an indication.

Summary

A condenser may just be the most important compartment of a microscope, working to converge random beams of light onto one objective to create the clearest image possible which, as any researcher will know, is vitally important for understanding the inner workings of the specimen in question.

It is always important to note that one condenser will not exactly trump all others.

Each of the four primary variants have their own unique function and benefits as well as individual drawbacks that can be made up for in the other designs, so it is all about picking the right apparatus for your specific situation.

Jennifer Dawkins

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