How to calculate the area of the field of view under the microscope
Reading pathological films under a microscope is one of the important aspects of a pathologist's work. The results of microscopic observation and recording are the scientific basis for clinical diagnosis. Only by using the microscope correctly and standardly, observing and recording the reading results can be scientific. As we all know, the imaging of a microscope is first magnified by the objective lens to image the specimen, and then it is magnified by the eyepiece and observed by the naked eye. The field of view of the image that can be displayed is determined by the field number of the eyepiece. It should be noted that the observation and recording described in this article are based on observation and recording through a microscope through the eyepiece. Other light paths that do not observe through the eyepiece are used to collect and record images, such as CCD, digital cameras, and software operation to collect images, etc., which will be described separately. The field number (FN) of the microscope eyepiece is different, and the size of the field of view that can be seen under the microscope is different. Different area areas have an impact on the positive rate count under the microscope. We should understand the relationship between the eyepiece field number and the field of view area. . The smaller the field number, the smaller the visible field area; conversely, the larger the field number, the larger the visible field area.
1 Identification of the number of fields of view of the eyepiece
The design and production of microscopes follow international standards. The field of view number is marked on the eyepiece of the microscope. For example, the Olympus BX50 microscope has an eyepiece field number of 22 (the English and numerical signs before the 22 value are the eyepiece classification name and magnification).
2 Actual field of view and calculation formula
On the plane of the specimen, the area (circular area) that the microscope can observe is called the actual field of view, also called the field of view. Use the following formula to calculate the area size.
3 objective lens magnification
Objective lenses are important optical components used for microscope imaging. Commonly used objective lens magnifications for biological microscopes are 4, 10, 20, 40 and 100. The commonly used high-power objective for pathological counting is 40.
4 intermediate magnification
Observe directly through the eyepiece without having to consider intermediate magnifications. The intermediate magnification refers to the magnification of the CCD interface, photographic eyepiece and CCD element added to the optical path. Because most of the microscopes used today are infinity imaging systems, with additional fluorescence observation, local difference observation, differential interference observation, etc., the components do not change the magnification and do not need to be considered.
5 Field of view area under commonly used eyepieces
The most commonly used eyepiece field number is 22. Various microscope manufacturers have successively designed and produced wide-field eyepieces with a field number of 25, and ultra-wide-field eyepieces with a field number of 265. There are also eyepieces with smaller field numbers of 18 or 20.
