(1) The imaging principle of the magnifying glass The optical lens made of glass or other transparent materials with a curved surface can magnify and image the object. The object AB located within the focal point F of the object side has a size of y, which is magnified into a virtual image A'B 'of size y'. (2) The imaging principle of document.write () microscope document.write () (3) Important optical technical parameters of document.write () microscope document.write () 1. Numerical aperture The numerical aperture has a close relationship with other technical parameters. It almost determines and affects other technical parameters. It is proportional to the resolution, proportional to the magnification, and inversely proportional to the depth of focus. As the NA value increases, the field of view width and working distance will decrease accordingly. 2. Resolution Cheap Pop Up Gazebo,Pop Up Gazebo,Pop Up Gazebo Tent,Steel Frame Gazebo Garden SHANDONG CAIFENG INTERNATIONAL TRADING Co., Ltd. , https://www.zihcaifeng.com
Magnification of magnifying glass document.write ()
Γ = 250 / f '
In the formula, 250--Bright visual distance, the unit is mm
f '-focal length of magnifying glass, unit is mm
The magnification refers to the ratio of the viewing angle of an object image observed with a magnifying glass to the viewing angle of an object without a magnifying glass within a distance of 250 mm.
document.write () Microscope document.write () and magnifying glass play the same role, which is to make a close-up tiny object into a magnified image for human eyes to observe. It's just that document.write () microscope document.write () can have higher magnification than magnifying glass.
Figure 2 is a schematic diagram of an object being imaged by document.write () microscope document.write (). For convenience in the figure, the objective lens L1 and the eyepiece L2 are represented by a single lens. Object AB is located in front of the objective lens, and the distance from the objective lens is greater than the focal length of the objective lens, but less than twice the focal length of the objective lens. Therefore, after passing through the objective lens, it must form an inverted enlarged real image A'B '. A'B 'is located at the object focal point F2 of the eyepiece, or at a position very close to F2. Then magnified by the eyepiece to a virtual image A "B" for eye observation. The position of the virtual image A''B '' depends on the distance between F2 and A'B ', which can be at infinity (when A'B' is on F2), or at the observer's clear vision distance ( When A'B 'is to the right of the focus F2 in the figure). The eyepiece functions like a magnifying glass. The only difference is that what the eye sees through the eyepiece is not the object itself, but the image of the object that has been magnified once by the objective lens.
During microscopic examination, people always want to be able to get clear and bright ideal images. This requires that the optical technical parameters of document.write () microscope document.write () reach a certain standard, and that when used, it must be Coordinate the relationship of various parameters according to the purpose of microscopy and the actual situation. Only in this way can the full performance of document.write () microscope document.write () be brought into full play and satisfactory microscopic examination results can be obtained.
The optical technical parameters of document.write () microscope document.write () include: numerical aperture, resolution, magnification, depth of focus, field of view width, poor coverage, working distance, etc. These parameters are not all as high as possible. They are interrelated and mutually restrictive. During use, the relationship between the parameters should be coordinated according to the purpose of the microscopic examination and the actual situation, but the resolution should prevail. .
The numerical aperture is abbreviated NA. The numerical aperture is the main technical parameter of the objective lens and the condenser lens, and is an important sign to judge the performance of the two (especially for the objective lens). The magnitude of its value is marked on the shell of the objective lens and condenser lens respectively.
The numerical aperture (NA) is the product of the sine of the refractive index (n) of the medium between the front lens of the objective and the object to be inspected and the half of the aperture angle (u). The formula is as follows: NA = nsinu / 2
Aperture angle, also known as "lens angle", is the angle formed by the object point on the optical axis of the objective lens and the effective diameter of the front lens of the objective lens. The larger the aperture angle, the greater the brightness of the light entering the objective lens, which is proportional to the effective diameter of the objective lens and inversely proportional to the focal distance.
When document.write () is observed in a microscope, if you want to increase the NA value, the aperture angle cannot be increased. The only way is to increase the refractive index n of the medium. Based on this principle, the water immersion objective lens and the oil immersion objective lens are produced. Since the refractive index n value of the medium is greater than 1, the NA value can be greater than 1.
The maximum numerical aperture is 1.4, which has reached the limit both theoretically and technically. At present, bromonaphthalene with a high refractive index is used as a medium. The refractive index of bromonaphthalene is 1.66, so the NA value can be greater than 1.4.
It must be pointed out here that in order to give full play to the role of the numerical aperture of the objective lens, the NA value of the condenser lens should be equal to or slightly larger than the NA value of the objective lens during observation. document.write () document.write ()
The resolution of document.write () microscope document.write () refers to the minimum distance between two object points that can be clearly distinguished by document.write () microscope, also known as "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 the NA factor of the objective lens and the wavelength of the illumination light source. The larger the NA value and the shorter the wavelength of the illumination light, the smaller the σ value and the higher the resolution.
To increase the resolution, ie reduce the value of σ, the following measures can be taken document.write ()
(1) Reduce the wavelength λ value and use a short-wavelength light source.
(2) Increase the medium n value to increase the NA value (NA = nsinu / 2).
(3) Increase the aperture value u to increase the NA value.
(4) Increase the contrast between light and dark.