If you have ever wanted to work in a lab, then chances are you have heard the term working distance. But what does it mean?
When it comes to working in a science lab, there are certain factors that should be taken into consideration, whether that be protective eyewear or chemical experiments.
However, the most common obstacle in any lab is how to find the best working distance between the microscope and the sample.
But what does working distance mean? In this article, we will explain what working distance means and how it can be used in a professional laboratory to ensure the best readings and results.
What Does Working Distance Mean?
If you have ever bumped a microscope into the slide without breaking the lens, then chances are you know the importance of working distance, even if you do not know what the term really means.
In most cases, the term working distance refers to the distance between the microscope’s lens and the surface of the slide or coverslip, which is where the specimen is often located.
A general rule of thumb is that the decrease in working distance will equal an increase in the total magnification, which can result in an increase in numerical apertures with high power objectives.
However, it is important to note that working distance can vary depending on the objective lens and its manufacturers.
For this reason, the working distance is now considered an important tool when using a microscope, as it can have a profound impact on the final result.
In fact, learning how to use the working distance can make the difference between an objective that is complicated to use and a microscope that works well for its intended purpose.
So if you want to learn how to use the working distance, you can follow the information we have compiled in the section below.
How To Use Working Distance
When it comes to locating the working distance on an objective lens, there are two methods that you can use. The first involves checking the inscription on the objective barrel, which is often considered the most accessible.
In most cases, this inscription will include the letters WD, which is an abbreviation for working distance. Next to this, you will also find the length in millimeters, which is often labeled like this: WD: 0.6 or 0.6 EL WD.
In this instance, the working distance for the microscope would be 0.6 millimeters, which means the lens will need to be adjusted to this distance to ensure a clean and sharp image of the specimen slide.
However, this is not the only way to find the working distance, as there are other methods that can also be used.
Our second method involves finding the working distance through the manufacturer’s specifications, which should come with the microscope or be available on their website.
In most cases, the working distance will take up a section of the specification sheet and will state the working distance for each lens.
If you are unable to obtain the working distance from these methods, then there is a third path that you can take. However, we would not recommend using this particular approach, as it could easily damage or smudge the objective lens.
For this method, you will need to take a digital caliper and measure the distance between the objective and the slide, which should deliver a somewhat accurate result.
While we do not recommend using this method, it remains a viable option if you are unable to locate the working distance.
What Is The Importance Of Working Distance?
Working distance is an important tool for various reasons, as it allows the user to observe a sample without having to push the lens into the specimen.
Because of this, working distance can be extremely useful when observing robust or harmful materials, as a long working distance provides enough separation between the observer and the specimen that they want to examine without issue.
However, this does not mean the higher power objective lenses are free from criticism, as most models will often require a higher numerical aperture and enough light to clearly see the sample.
This is because manufacturers who produce long working distance lenses will need to create the ideal balance between the need for a higher numerical aperture and the aberration corrections needed for a longer working distance.
Beyond this, longer working distance objectives can also help to reduce the risk of damage associated with higher power lenses.
While most objectives will feature a fine adjustment knob that can prevent possible damage, it is still possible to move the lens too close to the slide, which can result in the objective and coverslip coming into contact.
What Are The Different Long Working Distance Objectives?
In basic terms, long working distance objectives are a special kind of lens that are used to observe specimens from longer working distances, especially when compared to more conventional objective lenses.
In most cases, long working distance objectives are able to correct aberrations that could occur because of the vast distance, which results in a clean image for observations.
In the table below, we have outlined the differences between working distances, such as those on conventional achromatic objectives and long working distance plan achromatic objectives.
| Objective Model | Magnification | Working Distance |
| Achromatic | 4x | 37.4 mm |
| Achromatic | 10x | 6.6 mm |
| Achromatic | 40x | 0.64 mm |
| Achromatic | 100x | 0.19 mm |
| LWD Plan Achromatic | 4x | 11.98 mm |
| LWD Plan Achromatic | 10x | 11 mm |
| LWD Plan Achromatic | 40x | 2.9 mm |
| LWD Plan Achromatic | 100x | 0.12 mm |
If you are interested in purchasing one of these long working distance objectives, then it is important to note that most long working distance lenses can be extremely expensive.
However, this can also be somewhat beneficial, as you won’t need to replace the objective should it break or get scratched, as the price alone can make up for the initial investment and purchase.
What Objective Has The Shortest Working Distance?
According to our table, the objective lens with the shortest working distance is the 100x lens, which is commonly classed as an oil objective.
This means that the lens will need to be immersed in oil before you can obtain the required numerical aperture needed for the objective model.
Of course, this does mean that the lens will have to be very close to the slide coverslip, especially if the objective needs to be immersed in oil without touching the sample.
However, it is also possible to purchase 100x objective lenses that do not require the oil immersion, which means they still have a short working distance but without the mess.
A good example of this is the 100x dry objective from LW Scientific, which is a dry objective lens that does not require oil immersion and features a longer working distance than most conventional oil immersion competitors.
What Is The Best Long Working Distance Objective?
It is impossible to define a single objective as being the best one, since lens standards will often vary depending on the person and the specimens they want to observe.
However, we would personally recommend this 40x long working distance objective from BoliOptics, which comes with the benefit of upgraded optics and a longer working distance than most other lenses.
Final Thoughts
When it comes to using a microscope, it’s important to have a firm understanding of working distance and its benefits, as this can make a huge difference between a sharp image and a damaged lens.
In most cases, the increase in magnification will equal a lower working distance, which means you will get closer to the specimen and slide.
However, if you are concerned about the protection of the objectives, you may need to lengthen the working distance to avoid potential accidents.
Ever since I was a little girl, I have been fascinated by science. Every holiday I would ask for the newest science kit, and spend weeks learning with it.
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