What do you know about the microscope terminology used in metallographic analysis?
Numerical Aperture
Numerical aperture is the main technical parameters of the objective lens and condenser lens of the metallurgical microscope, numerical aperture abbreviation NA, is to judge the two (especially for the objective lens) the performance of the important signs of high and low. The size of its value, respectively, engraved in the objective lens and the shell of the condenser lens.
Numerical aperture (NA) is the objective lens before the lens and the object to be examined between the refractive index of the medium (n) and the aperture angle (u) half of the sine of the product. Expressed by the formula as follows: NA = nsinu/2
Resolution
The resolution of the metallurgical microscope is the resolution of the microscope can be clearly distinguished by the * small distance between the two object points, also known as the discrimination rate. Its calculation formula is σ = λ / NA
Where σ is the * small resolution distance; λ is the wavelength of light; NA is the numerical aperture of the objective lens. The resolution of the objective lens is determined by the NA value of the objective lens and the wavelength of the illumination light source, the larger the NA value, the shorter the wavelength of the illumination light, the smaller the σ value, the higher the resolution.
Magnification and Effective Magnification
Because of the two magnifications by the objective lens and the eyepiece, the total magnification Γ of the microscope should be the product of the objective lens magnification β and the eyepiece magnification Γ1: Γ = βΓ1
Obviously, a microscope can have a much higher magnification compared to a loupe, and the magnification of a microscope can be easily changed by switching the objective and eyepiece with different magnifications.
Depth of Focus
Depth of focus is short for depth of focus, i.e., when using a microscope, when the focus is on a certain object, not only can the points on the plane of the point be seen clearly, but also within a certain thickness above and below the plane, it can also be seen clearly, and the thickness of this clear part is the depth of focus. This is particularly important in video microscopy.
Field of View Diameter
When observing a microscope, 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, also known as the width of the field of view, is the actual extent of the object being examined that can be accommodated within the circular field of view seen under the microscope. The larger the diameter of the field of view, the easier it is to observe.
Coverage Difference
The optical system of a microscope also includes cover slips. Because the thickness of the coverslip is not standardised, the path of light from the coverslip into the air after refraction is altered, resulting in a phase difference, which is known as the coverage difference. This is the coverage difference, which affects the quality of the metallurgical microscope.
Working Distance
The working distance is also called the object distance, that is, the distance between the surface of the lens in front of the objective lens and the object to be examined. Mirror inspection, the object to be examined should be in the objective lens between double to two times the focal length. Therefore, it is two concepts with the focal length, usually used to say that the focus, in fact, is the adjustment of the working distance of the metallurgical microscope.
