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Dark field microscopefilter

From the life sciences and medicine to semiconductors and jewelry, microscopes have become essential tools for many industries. They bring details to light that the naked eye could never see, but the insights viewers gain can be skewed if they don't know how large the image is. That's what field of view expresses.

The tradeoff between FOV and magnification means that observers have several factors to take into consideration when they choose how much power is right for their project. Two of these factors are resolution and depth of field.

Phase contrastmicroscope definition

The 3D images that stereo microscopes provide also require consideration of depth of field, or DOF. The calculations aren't as straightforward as those for FOV, but a higher magnification is directly proportional to a greater depth of field. As with resolution, if observers need to distinguish between multiple layers of their specimen, they may need higher magnification at the expense of FOV. However, stereo microscopes typically have a larger default FOV than conventional compound microscopes, so the tradeoff is less with this type of scope.

Dark field microscopediagram

In the above equation, note that field of view is inversely proportional to magnification power; a lower total magnification allows for a larger field, and a higher magnification results in a smaller field. This is to be expected, because the closer an observer zooms into an object, the smaller the window they view.

Once the field number and magnifying power of each lens in use are known, a simple equation exists to help observers find the total field size of the image in view. If the objective lens is the only magnifier in use, the field size is equal to the field number divided by the objective magnification of the lens, or:

The field number can be easily located on a microscope, as it's typically written on the side of each lens, next to its magnifying power. For example, if the numbers on a microscope's objective lenses are 10X/15, 40X/20, and 100X/25, the objective magnifications would be 10X, 40X, and 100X, while the field numbers would be 15, 20, and 25, respectively.

The first step in determining the FOV is to find the field number on the objective lens. This number gives the diameter of the microscope field, assuming no other eyepieces or magnifiers are added.

Advantagesof dark field microscope

Imageof dark field microscope

Defined as the minimum distance at which an observer can distinguish two adjacent points, resolution increases with magnification. That means especially detailed objects may require the superior resolution that comes with higher magnification, even if the FOV is reduced.

Whether you're examining a cell with an optical microscope or soldering components onto a printed circuit board (PCB), knowing the size of the object in view helps you complete your work more effectively. For example, knowing the size of a microscope field can help the observer determine how large an organelle within a microorganism is, and could also give other insights about important image features.

As an example, a microscope having an objective lens with 100X magnification power and a field number of 25 mm would have a field size of 25 mm/100, or 0.25 mm. Similarly, if the same microscope added an eyepiece having a magnification power of 20X, the field size would be 25 mm/(100*20), or 0.0125 mm. Because the field size can be quite small, instead of expressing field size in terms of millimeters, some observers may multiply their value by 1,000 to convert their units to micrometers

The field observation window also decreases quite rapidly when auxiliary lenses are added. A single eyepiece with a magnification power of 10X reduces the field of view by a factor of 10, so observers adding extra lenses should know just how much width they'll lose.

Advantages and disadvantagesof dark field microscope

Fluorescencemicroscope

FS = FN/(ME*MO), where  FS = field size, FN = field number, ME = eyepiece magnification, and MO = objective magnification

A measurement of the diameter of the visible image, field of view (FOV) clarifies how much of the object the viewer is actually observing. This allows the viewer to analyze the specimen more clearly, perform any needed operations with greater precision, and have a better understanding of what they see. In this article, we'll show you how to calculate field of view, what it is, and some FOV differences for compound and stereo microscopes. Here's a deeper look.

Calculating a microscope’s field of view differs somewhat for compound and stereo microscopes. Both involve a calculation based on the total magnification of the microscope and a parameter on the lens, but stereo microscopes have other factors to consider.

FOV is simply a measurement of the diameter of the image that the viewer can see. It's typically expressed as the diameter in millimeters of the observer's field of vision, and is used to quantify the size of the object under inspection.

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If an eyepiece is added, the field size is equal to the field number divided by the total magnifying power of the entire assembly. Since magnifying power compounds geometrically, the total magnifying power is the product of the microscope eyepiece and microscope objective lens. In this case, the field size can be expressed as: