Field of View Diameter
One of the basic but most important concepts you need to understand when using a compound light microscope is field of view. For more information about this microscope, http://www.compound-light-microscope.com may be of great help.
Also known as the field number, the field of view refers to the diameter of the microscope’s circle of view when you look through its eyepiece hole. The field of view is measured in millimeters (mm) at the intermediate image plane. When it comes to field of view, always remember that the bigger field of view you need, the lower the magnification you should use!
Understanding How the Field of View of Microscope Works
The diaphragm of a microscope is part of the substage condenser, so-called because the condenser is normally found under the microscope’s stage. It’s the opposite, of course, with inverted microscopes. The diaphragm is used to manipulate the angle of light coming from the condenser. The diaphragm, more specifically its eyepiece opening, is typically responsible for determining the view field size.
To obtain the numerical equivalent of the view field size, get the field of view number of the microscope and then divide it with the objective magnification you’re using.
At times, a supporting or secondary lens would be placed in between the microscope’s eyepiece and objective lens. In such cases, make sure you take note of the changed magnification caused by the secondary lens when calculating the view field size. Keep in mind as well that both the system design of the microscope’s objective lens and its field number has limitations that affect the view field size.
The first microscope models used to have approximately eighteen millimeters or even lower than that for its field of view. Special lenses, however, such as flat-field and apochromat objective lenses, make the microscope’s field of view go even beyond twenty-eight millimeters!
Today, you’ll often find the field diaphragm of your microscope either between the lenses or before its optical system. Manufacturers of modern compound light microscopes also make sure that the field diaphragm and its lenses are located separately and far from the microscope’s intermediate image plane. If not, surface debris, dust, or any other unwanted artifacts could be magnified and projected together with the sample or specimen.
Time and experience will soon make you familiar with common figure combinations in microscope use. When you are viewing a specimen at 10x magnification, for instance, then its field of view would normally range from sixteen to eighteen millimeters. If you are viewing the sample at even lower magnification, say 5x, then field of view could go as high as twenty millimeters. Also, you’ll notice that there are more details to see when you are viewing at lower power and with greater field of view.
Opening size of your diaphragm also affects field of view especially because they rely on the objective’s off-axial aberration.
Field of View and Determining the Size of a Sample
Knowing the field of view will help you determine the size of the sample you’re analyzing. If the field of view you’re using is two millimeters and the sample is approximately a third of its size then simply multiply its measurement (1/3) with the field of view number (2) and you’ll obtain the approximate object size and that’s 3 millimeters.
You can also try using a ruler to determine object size but this is only possible when you’re observing a sample or specimen at low power magnification. It’s difficult but possible to get the same results when you’re working at high power magnification.
For an example, let’s say that the low power field of view you’re using is approximately 2.5 millimeters. If you’re operating at low power magnification, specifically at 100x with both objective and eyepiece at 10x, and then your high power magnification is set at 400x by using the same eyepiece but a 40x objective lens this time. How wide could the object be at 400x?
The answer: the sample or specimen is one-fourth as wide by multiplying the low power field of view with the low power magnification then dividing the result with the high power magnification.
Field of View Improves with a Deformable Mirror
In 2006, a research scientist in an New York Institute had utilized deformable mirror technology produced by a Boston firm to be able to view tiny samples or specimen at greater distances and view enlarged images of tiny objects in larger areas. Their breakthrough research has made it possible to use a typical microscope and enjoy a forty millimeter field of view with a resolution of 1.5 um. Such a discovery had helped the research institute progress with their projects and who knows if someday, this improvement could help the entire world advance as well.
