The microscope condenser lens on a compound microscope gives you control over how the substage lighting is projected onto the specimen. Its primary function is to provide uniform light intensity over the specimen to create a sharper and cleaner view of the specimen.
Used with an aperture diaphragm, it also allows you to adjust the cone of light projected into your objective lens to get the perfect field of view for looking at your specimen.
A condenser is increasingly necessary as you use higher magnification levels. The most common condenser for a home or lab microscope (known as a compound light microscope) is a 1.25 NA Abbe condenser used with an iris diaphragm.
Where is the Condenser on a Microscope?
Your condenser usually sits below the microscope stage, which is why we classify it as a ‘substage microscope part’. It is in fact attached to the stage. As you raise and lower the stage, the condenser will move with it.
If you own a cheaper kids’ microscope, there’s a good chance you don’t have a condenser. Condensers usually come with microscopes from about the $150 range and up, with the most common condenser being an Abbe condenser.
What does the Condenser do on a Microscope? (Functions)
The condenser performs several key functions:
- Distributing light evenly over the specimen to remove lighting imperfections;
- Aberration correction;
- Controlling the angle of the cone of light projected into the objective lens above.
1. Light Distribution
Before the condenser was invented, scientists would often see imperfections in the light source that harmed image quality. One common issue was that the glowing filament in a halogen light bulb was visible under the specimen, which significantly distorted the image that reaches the eye.
Ernst Abbe solved that issue with his Abbe condenser, which he invented in 1870.
2. Aberration Correction
Some higher-end condensers correct of spherical and chromatic aberration of light.
Condensers that correct chromatic aberration prevent the rainbow effect (‘color fringing’) where it looks like there is a colored outlined around an image.
Condensers that correct spherical aberration prevent blurry edges around images that occur when the light from the edge of a spherical lens does not reach the same focal point as the rest of the lens.
3. Light Angle Correction
The condenser itself is rarely adjusted for beginner microscopy activities. However, you can raise it and lower it so the cone of light is closer or farther from the specimen. This affects the angle of the light as it enters the objective lens above. At 1000x, you’d want it very close to the specimen, while at lower magnifications it can be farther away.
The thing you will adjust is the aperture diaphragm which sits above and works with the condenser. That’s discussed next…
The Aperture Diaphragm
There is another microscope part – the aperture diaphragm – which works together with the condenser, and in fact is so important to the role of the condenser that it’s sometimes called the ‘condenser diaphragm’. You can adjust the diaphragm to control the numerical aperture [ref] of the cone of light projected from the condenser.
In layman’s terms, you need to make sure the cone of light is perfectly projected into the objective:
- If your aperture is too wide, you will get glare and poor contrast.
- If your aperture is too narrow, you will get light refraction and diffraction which, again, distorts the image.
It’s a goldilocks game – you want the aperture to be just right so you can see the specimen perfectly.
Each objective on your microscope has a different aperture. So when you rotate objective lenses on the objective turret (for example, from 10x to 40x), you’ll also want to adjust the aperture on the aperture diaphragm so the field of view is perfect.
> Read More: What Function is performed by the Diaphragm of a Microscope?
Microscope Condenser vs Diaphragm
People will often say a diaphragm is part of the condenser, but they are two separate tools that work together. Their functions are so intertwined, however, that you’ll often buy a condenser and diaphragm as a ‘kit’.
But you might notice that many kids’ microscopes have disc diaphragms but not condensers.
Generally, the condenser creates even light distribution and aberration correction, while the diaphragm controls the aperture of the cone of light that the condenser produces.
Without the diaphragm, the condenser is not nearly as effective.
Types of Microscope Condenser
There are four main types of condenser for a microscope. You’ll find that most microscopes you buy form the shop will have an Abbe Condenser (or no condenser at all for kids’ microscopes). But you can buy aftermarket condensers for specific purposes.
1. Abbe Condenser
The Abbe condenser is industry standard because it’s cheap, effective, and produced en masse. You’ll likely have a 1.25 NA Abbe condenser in your microscope.
While these microscopes are cheap and sufficient for most beginner microscopy tasks, they don’t accommodate for spherical lens aberration or chromatic lens aberration.
Spherical lens aberration occurs when the edges of a curved lens do not direct light rays to the same focal point as the rest of the lens. Commonly, this leads to a blurred final image, particularly at wider aperture settings.
Chromatic lens aberration occurs when all colors are not focused to the same focal point. The end result of this is ‘color fringing’ – a phenomenon where colors appear around the edges of objects.
2. Aplanatic Condenser
(Best for Spherical Lens Aberration Correction)
An aplanatic condenser corrects for spherical lens aberration. This means they are able to correct for the aberration that occurs due to the surface of a lens being spherical in shape. The edges of the lens will usually have a different focal point to the center, leading to blur.
To address this, aplanatic condenser has many layers of lenses inside it which effectively flatten out this effect, allowing the light to concentrate on one central location.
However, aplanatic condensers are not necessarily good at color correction. You may still find there is chromatic lens aberration, where you get ‘color fringing’, as discussed earlier.
3. Achromatic Condenser
(Best for Chromatic Lens Aberration Correction)
An achromatic condenser corrects for color fringing by ensuring all light waves across the color spectrum meet at one focal point. This allows for a much cleaner image, and is preferred by many people who do photomicrography.
However, they do not all necessarily also adjust for spherical aberration, meaning you may still get a blurring effect.
4. Aplanatic-Achromatic Condenser
(Achieves both Spherical and Chromatic Aberration Correction)
The final, and by far most expensive, microscope condenser is the aplanatic-achromatic condenser, which achieves both spherical and chromatic aberration correction.
Because this type of condenser adjusts for both types of aberration, it is very popular among photomicroscopists. However, the price point is a barrier to most of us.
While you might think this must be the best type of condenser, it still isn’t a catch-all solution. It’s hard to find one condenser to suit all situations [ref]. Lower powered objectives need broader light cones, while higher powered objectives need very narrow light cones, and it’s hard to achieve this whole range in one condenser.
A microscope condenser is an important microscope part because it helps to correct the light that passes through the specimen and into the microscope objective. Without a condenser, the quality of the image that you see is significantly diminished, particularly at high magnification levels.
While most people will get by with a simple 1.25 NA Abbe condenser, higher-end photomicroscopists and people working with high power oil immersion methods might light to step up to condensers that correct for aberration (spherical and chromatic) to create an even better quality image.
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