Introduction to general optical microscopes
The microscope is the primary tool for observing cells. According to different light sources, they can be divided into two categories: optical microscopes and electron microscopes. The former uses visible light (UV microscope uses ultraviolet light) as the light source, while the latter uses electron beam as the light source. Ordinary optical microscopes and laser confocal microscopes are both optical microscopes.
Ordinary biological microscopes are composed of three parts, namely: ① illumination system, including light source and condenser; ② optical magnification system, consisting of objective lens and eyepiece, which is the main body of the microscope. In order to eliminate spherical aberration and chromatic aberration, both eyepiece and objective lens are composed of complex Composed of lens group; ③ mechanical device, used to fix materials and facilitate observation.
Whether a microscope image is clear depends not only on the magnification, but also on the resolution of the microscope. Resolution refers to the ability of the microscope (or the human eye 25cm away from the target) to distinguish the smallest distance between objects. The size of the resolution determines Based on the wavelength of light, the lens opening ratio and the refractive index of the medium, the formula is expressed as:
R=0.61λ/N. A. N. A. =ｎsinα/2
In the formula: n=refractive index of medium; α=mirror aperture angle (the opening angle of the specimen to the objective lens aperture), N.A.=numeric aperture. The mirror angle is always less than 180°, so the maximum value of sina/2 must be less than 1.
The refractive index of glass used to make optical lenses is 1.65~1.78. The closer the refractive index of the medium used to that of glass, the better. For dry objective lenses, the medium is air, and the lens opening ratio is generally 0.05~0.95; for oil lenses, cedar oil is used as the medium, and the lens opening ratio can be close to 1.5.
The wavelength of ordinary light is 400~700nm, so the resolution value of the microscope will not be less than 0.2μm. The resolution of the human eye is 0.2mm, so the maximum magnification of the general microscope design is usually 1000X.
