What Does the Objective Lens Do on a Microscope
The objective lens is one of the core technologies that work to power a microscope, but how exactly does it do that? It implements many complicated moving pieces that all work together to help provide magnification, which can vary depending on the type of objective lens you have.
If you’ve wanted to understand the objective lens and its inside, then this is a resource for you. This article will help break down these components, what types of objective lenses exist, and who invented this technology.
What Are The Components of an Objective Lens?
As one might expect, digital microscopes are tightly designed and engineered devices that include many different lenses and other components within one housing.
As Florida State University’s online microscopy portal explains, these can be configured based on the microscope’s application, but many things stay the same across objectives.
With their example, we’ll break down some of these components, both internally and externally.
Nosepiece Threads
This metal threading seen at the top of the implement helps connect it to the larger microscope. This will often be made of a durable metal as it needs to seal all light out and keep the objective securely in place with no wriggle room whatsoever.
Decorative Barrel
In theory, an objective lens could operate without its outer metal barrel, leaving moving components exposed and possibly making lens elements vulnerable to elements or shock.
So, the entire mechanism is situated inside a metal casing that keeps it secured and allows for text to be printed. This text will include specifications and the manufacturer of your objective lens.
Immersion Medium Correction Collar
We’ll explain immersion mediums further in this article later on, but for now, you can think of this almost like the focus ring around the lens of a DSLR camera. This twistable ring will manipulate the lenses inside to correct them for a specific type of immersion properly, whether that be oil, glycerin, or water.
This mechanism allows one single objective to be compatible with multiple immersion types!
Magnification Color Code
Most objective lenses will feature a colored strip printed around the lens’s circumference, which will indicate its level of zoom. These are standardized across manufacturers, and are as follows:
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Black = 1x
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Brown = 2x
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Red = 4x
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Yellow = 10x
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Green = 20x
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Light Blue = 40x
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Dark Blue = 63x
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White = 100x
Front Lens Elements
The front lens, the one at the bottom that may make contact with a specimen, is sometimes actually composed of two lenses, a hemispherical front lens and a meniscus lens. These work together to capture light rays directly and are protected by a front lens assembly house, as well as a spring-loaded retractable nose cone that helps avoid collision damage between the lens and a specimen.
Moveable Lens Group
Our Immersion Medium Correction Collar brings a group of lenses that can move and shift within one another to facilitate the changes in numerical aperture.
By twisting and altering slightly, these movable lenses can provide a different level of magnification, which enables different immersion mediums to offer high-quality visuals.
What Are The Types of Objective Lenses?
Objective lenses do not come at one single specification. Instead, they are just as interchangeable and customizable as any other part of a microscope, with certain microscopes able to transition across multiple objectives on the fly.
This means that they can be tailored to your individual uses, so you can find a solution that works best for you instead of adapting your workflow to comply with existing standards. But, this also means you need to understand the types of microscope objectives to know which one is best for you.
Luckily, Microscope Spot has a great article on these types and what each one is best at.
Scanning Objective Lens
These are low-level magnification lenses, offering only four times magnification of the sample, which when combined with an eyepiece lens leads to about 40x total zoom.
These are best when a researcher is aiming to examine an entire slide or sample at one time, with the intent of documenting its structure, shape, size, and other overarching factors.
This is best on a multiple-lens configuration, as you will likely want to dive deeper for a higher level of detail later on, but this lens still provides useful oversight of an entire sample.
Low Power Objective Lens
When looking at a glass-slide sample, these objective lenses are the simplest available option, even if they lack power compared to later options.
With a 10x magnification in the objective, leading to a total of 100x magnification, this lens can still provide decent magnification without the need for immersion fluids or other enhancements. Instead, it provides low-hassle and low-risk options for samples that do not require the extra arduous preparation procedures for high-definition scanning.
High Power Objective Lens
Now things start to get deep, as these 40x lenses combine with an eyepiece for a total of 400x magnification. This is commonly known as the highest possible level of magnification without the assistance of an immersion, which we’ll talk about in our next category.
Still, there is a place for these strong objective lenses to provide high depth and quality to specimens.
Immersion Objective
Immersion objective lenses offer a staggering 100x magnification, which results in 1000x magnification. However, to achieve this, the lens must be built with a refractive index greater than that of air, which can cause blurring and loss of data.
The technique of oil and water immersions was invented to remedy this, which involves inserting a drop of oil or water between the objective and the sample. These fluids offer a refractive index more fitting for the lens, and each one has its own numerical apertures.
The result is that oil can produce the highest resolution results but offers little in terms of depth of field, so it struggles with samples that feature cover glass. Meanwhile, water has slightly lesser resolution but does possess a deeper depth of field, making it an optimal solution for specimens submerged in water and beneath a cover glass.
Who Invented The Objective Lens?
While microscopes date back to Zaccharias Janssen in the late 1500s, these were single implements that did not feature an objective like what is seen on modern compound microscopes.
Instead, according to Bite-Sizeite Size Bio, the first known reference of a microscope with an objective lens came from the publication of ‘Micrographia’ in 1665 by Robert Hooke. This design was then taken by Christopher Cock in London, where he created a microscope with a bi-convex objective and eye-lenses and a field lens to increase the field of view.
Hooke is credited with aiding multiple advancements in microscopy, including the use of a stand that allowed for adjustments and a primitive light condenser made with an oil lamp and a water-filled globe. Hooke is also known for discovering and naming the cell in 1665.
While these early objective lenses and microscopes may seem primitive, it is important to recognize that these older implements help build the high-magnification objective lenses that we have today.
In that same vein, we can also think that what we currently have is only a stepping stone to the microscopes of the future, which may make our current implements look silly in comparison.
This could be done through advancements in machine vision, improved field of view, or other unheard-of techniques that partner with emerging technologies.
Conclusion
Objective lenses are complex devices built with many components that all exist in harmony and work with one another. External lens adjusters allow for compatibility with multiple immersion mediums, and widely differing zoom levels allow microscopes to offer multiple perspectives on a specimen.
This is the result of hundreds of years of innovation dating back to the son of a lensmaker who helped lay the foundation for what microscopes have become.
Sources:
Carl Zeiss Microscopy Online Campus - Microscope Objectives | zeiss-campus.magnet.fsu.edu
Microscope Post - Types of Objective Lens & Their Functions | Microscopepost.com