Everything You Need To Known About Microscopy: Field Of View

Microscopes have opened up a whole new world for us to explore. From material science to ecology to biology – microscopes have expanded every scientific field, and they continue to do so every day.

Everything You Need To Known About Microscopy: Field Of View

Microscopes are the definition of small and mighty, as while the mechanism is fairly simple (essentially, all you are doing is making a small thing bigger!), we are also expanding our vision and understanding and interpreting details that are not visible to the naked eye. 

The microscopy field can be an exciting and satisfying place, where no two days are the same and you get to explore and discover many different aspects of the world around you.

However, before we jump straight into microscopy, it’s important to understand the underlying concepts and basic principles behind it. 

For instance, understanding how light refraction works, concepts of resolution and magnifications, and other principles including what determines the field of view and, thus, how to calculate it. 

What Is The Field Of View?

The phrase field of view refers to the magnitude by which the observable world can be perceived at any given moment. It concerns the significance of visibility, which is generally measured at an angle, that an optical instrument or the eye is susceptible to. 

When looking at the human eye, the term field of view is often used to describe the visual field.

This is typically measured by a horizontal arc slightly above 210 degrees – demonstrating that the human eye’s field of view is everything in front of us, as long as it is within the proclaimed range. 

Likewise, when looking at humans, it is only natural that optional instruments and animals also have different fields of view.

Below, you will find an explanation of what is the field of view in microscopy, how this is then calculated, and any affecting factors. 

What Microscopy Field Of View

In terms of a microscope, when measuring the microscopy field of view you will be looking at the diameter of the viewing field that is deliberated at an intermediate plane of angle.

Generally speaking, when looking into the eyepiece of a microscope, this is the diameter of the circular area that you are able to see. 

In instances where optical microscopes are used, for example, light microscopes, the field of view is resolved by the diameter of the window to the eyepiece field diaphragm.

This can be found either in the middle of the ocular lens and the objective lens or situated before the two lenses. 

In addition, this is also dependent on the objective lens magnification, or more specifically, the overall ocular and objective lens compound magnification. 

What Determines The Microscopy Field Of View?

As previously mentioned, the field of view can be determined by looking at the diameter of the diaphragm, as well as the lenses’ magnification. Imprinted besides the microscope’s eyepiece is where you will generally find these numbers. 

If you’re looking for magnification, it is usually the first number that ends with an ‘X’. Moreover, the diameter can be found within the second number.

This is commonly known as the field of view number, or straightforwardly, the field number, and it is demonstrated in millimeters. 

The highest field diameter can typically fall between the ranges of 18 to 28 millimeters (sometimes even higher!), and this is all dependent on how advanced the objective lens is and whether or not the lens is a unique model of a flat field objective.

How Can You Calculate The Microscope’s Field Of View? 

Looking at the expressed microscopy field of view above, we are then able to reason that the viewing field size specimen plane is the same as the field number then divide this by the magnification of the objective lenses, or in simple terms: Field Size = Field Number/ Objective Magnification.

Everything You Need To Known About Microscopy: Field Of View

Typically, the field number of a specific microscope eyepiece can be constricted due to its magnification and dimensions of the field diaphragm; although, this can only be somewhat affected if magnified auxiliary lenses are situated in the middle of the ocular and objective lenses

In such cases, the compounded magnification of the auxiliary and objective lenses can be determined by multiplying these two factors together, demonstrating the total magnification that should then be used when calculating the field of view size. 

For Example:

When a maximum field diameter is 20 millimeters of the diaphragm, and the microscopes have two dedicated lenses, each having a 20x and 10x magnification, the view field size can then be calculated as 20 millimeters divided by 200, equally to 0.1 millimeters magnifications. 

On the other hand, if you find the total magnification to be 20x, then the field view will equate to 1 millimeter – allowing you to see a bigger aspect of the sample. However, since the magnification is low, you won’t be able to see any minute details. 

For this reason, microscopes are only a few centimeters wide, whereas the field size of electron transmission microscopes can be as small as a single nanometer to a couple of picometers – ensuring you can see even the smallest of details. 

How Can Magnification Affect The Field Of View?

When looking at the previously mentioned examples, it can be seen that the magnification of a microscope has an adverse effect on the presumed field of view.

Essentially, the more a sample is magnified, the less amount of detail you will be able to see.

To highlight this, an eyepiece or ocular lens with a 5x magnification typically has a 20-millimeter field of view, whereas an eyepiece of 10x magnification will have a smaller field of view running from 16 to 18 millimeters.

The higher the magnification increases, the more noticeable the difference will become, especially when over one hundred or more.  

Is The Field Of View Important?

Yes! This microscopy field of view is definitive of how much, and in how much detail, we are able to see of a specific sample.

Being able to understand how this works provides you with the tools to establish your expectations when you’re looking into a microscope, allowing you to manipulate the magnification strength. 

For example, if you were to look at an insect sample. If you wanted to see the whole insect under the microscope, you would need to set the microscope to a low-power lens.

On the other hand, if you wanted to look closely at the specimen – for areas such as the wings or a certain body part – then you would have to increase the magnification and move the slide slightly to make sure the insect is centered in the microscope viewing field. 

Final Thoughts

Microscopy is a fascinating field of study. The microscopy field of view is determined by the overall visible area when looking at the sample plane.

Although, this can be affected by a number of factors including the magnification and the diameter of the diaphragm. Hopefully, this guide has provided you with everything you need to know about microscopy and the field of view.

Jennifer Dawkins

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