Biological Microscope Related Parameters
Numerical aperture (NA)
The numerical aperture is abbreviated as NA, and the numerical aperture is the main technical parameter of the objective lens and the condenser lens, and is an important symbol to judge the performance of the two (especially for the objective lens). The size of its numerical value is respectively marked on the casing of the objective lens and condenser lens. It is the product of the refractive index (n) of the medium between the front lens of the objective lens and the object to be inspected and the sine of the half of the aperture angle (u). The formula is as follows: NA=nsinu/2. It is proportional to the resolution, proportional to the magnification, and inversely proportional to the depth of focus. As the NA value increases, the width of the field of view and the working distance will decrease accordingly.
Numerical Aperture (NA) Resolution
·Resolution
The resolution of the microscope refers to the minimum distance between two object points that can be clearly distinguished by the microscope, also known as the "discrimination rate". The calculation formula is σ=λ/NA where σ is the minimum resolution distance; λ is the wavelength of light; NA is the numerical aperture of the objective lens. The resolution of the visible objective lens is determined by two factors: the NA value of the objective lens and the wavelength of the illumination source.
Magnification and effective magnification
After two times of magnification by the objective lens and the eyepiece, the total magnification of the microscope is the product of the magnification of the objective lens and the magnification of the eyepiece, and the limit of the magnification of the microscope is the effective magnification.
depth of focus
Depth of focus is the abbreviation of depth of focus, that is, when using a microscope, when the focus is on a certain object, not only all points on the plane of this point can be seen clearly, but also within a certain thickness above and below the plane, To be clear, the thickness of this clear part is the depth of focus. If the depth of focus is large, you can see the entire layer of the object under inspection, while if the depth of focus is small, you can only see a thin layer of the object under inspection.
Field diameter
The bright circular area seen is called the field of view, and its size is determined by the field diaphragm in the eyepiece. The diameter of the field of view is also called the width of the field of view, which refers to the actual range of the inspected object that can be accommodated in the circular field of view seen under the microscope. The larger the diameter of the field of view, the easier it is to observe.
Field of view diameter = number of field of view of the eyepiece / magnification of the objective lens
poor coverage
Due to the non-standard thickness of the cover glass, the light path after the light enters the air from the cover glass changes, resulting in a phase difference, which is poor coverage. Internationally, the standard thickness of the cover glass is 0.17mm, and the license The range is 0.16-0.18mm, and the phase difference in this thickness range has been calculated in the manufacture of the objective lens. The 0.17 marked on the objective lens housing indicates the thickness of the cover glass required by the objective lens.
Working distance (WD)
The working distance is also called the object distance, which refers to the distance from the surface of the front lens of the objective lens to the object to be inspected.
