How may the microscope's resolution be increased?
The composition and structure of an optical microscope An optical microscope generally consists of a stage, a spotlight lighting system, an objective lens, an eyepiece, and a focusing mechanism. The stage is used to hold the object to be observed. The focusing mechanism can be driven by the focusing knob to make the stage move up and down for rough adjustment and fine adjustment, so that the observed object can be focused and imaged clearly.
Its upper layer can move and rotate precisely in the horizontal plane, and generally adjust the observed part to the center of the field of view. The spot lighting system is composed of a light source and a condenser. The function of the condenser is to concentrate more light energy to the observed part. The spectral characteristics of the illuminating lamp must be compatible with the working band of the microscope receiver.
The objective lens is located near the object to be observed, and it is the lens that realizes the first level of magnification. Several objective lenses with different magnifications are installed on the objective lens converter at the same time, and the objective lenses with different magnifications can enter the working optical path by rotating the converter. The magnification of the objective lens is usually 5 to 100 times. The objective lens is the optical element that plays a decisive role in the quality of the image in the microscope.
Commonly used are achromatic objective lenses that can correct chromatic aberration for two colors of light; higher quality apochromatic objective lenses that can correct chromatic aberration for three kinds of color light; can ensure that the entire image plane of the objective lens is flat to improve the field of view Flat field objectives with marginal image quality. Liquid immersion objectives are often used in high-magnification objectives, that is, the refractive index is 1 between the lower surface of the objective lens and the upper surface of the specimen sheet.
5 liquid, it can significantly improve the resolution of microscopic observation. The eyepiece is a lens located near the human eye to achieve the second level of magnification, and the magnification of the lens is usually 5 to 20 times. According to the size of the field of view that can be seen, eyepieces can be divided into two types: ordinary eyepieces with a smaller field of view and large-field eyepieces (or wide-angle eyepieces) with a larger field of view.
Both the stage and the objective lens must be able to move relative to each other along the optical axis of the objective lens to achieve focus adjustment and obtain a clear image. When working with a high-magnification objective lens, the allowable focusing range is often smaller than microns, so the microscope must have a very precise micro-focusing mechanism. The limit of the magnification of the microscope is the effective magnification, and the resolution of the microscope refers to the minimum distance between two object points that can be clearly distinguished by the microscope.
Resolution and magnification are two different but related concepts. When the numerical aperture of the selected objective lens is not large enough, that is, the resolution is not high enough, the microscope cannot distinguish the fine structure of the object. At this time, even if the magnification is excessively increased, the obtained image can only be an image with a large outline but unclear details. , called the invalid magnification.
Conversely, if the resolution meets the requirements but the magnification is insufficient, the microscope has the ability to resolve, but the image is still too small to be clearly seen by human eyes. Therefore, in order to give full play to the resolving power of the microscope, the numerical aperture should be reasonably matched with the total magnification of the microscope. The spotlight lighting system has a great impact on the imaging performance of the microscope, but it is a link that is easily overlooked by users.
Its function is to provide sufficient and uniform illumination of the object surface. The light beam sent by the condenser should ensure that it fills the aperture angle of the objective lens, otherwise the highest resolution that the objective lens can achieve cannot be fully utilized. For this purpose, the condenser is equipped with a variable aperture diaphragm similar to that in the photographic objective lens, which can adjust the size of the aperture, and is used to adjust the aperture of the illumination beam to match the aperture angle of the objective lens.
By changing the lighting method, different observation methods such as dark object points on a bright background (called bright field illumination) or bright object points on a dark background (called dark field illumination) can be obtained, so as to better discover and observe the microstructure. An electron microscope is an instrument that uses electron beams and electron lenses instead of light beams and optical lenses to image the fine structures of substances at very high magnifications based on the principle of electron optics.
The resolving power of an electron microscope is represented by the minimum distance between two adjacent points that it can resolve. In the 1970s, the resolution of the transmission electron microscope was about 0.3 nanometers (the resolving power of the human eye was about 0.1 mm). Now the maximum magnification of the electron microscope exceeds 3 million times, while the maximum magnification of the optical microscope is about 2000 times, so the atoms of some heavy metals and the neatly arranged atomic lattices in the crystal can be directly observed through the electron microscope.
