What is the difference between a phase contrast microscope and an ordinary microscope?
(1) Principle and structural characteristics of phase contrast microscope
Light waves have different amplitudes (brightness), wavelengths (color), and phases (referring to the positions that light waves can reach at a certain time). When light passes through an object, such as changes in wavelength and amplitude, it can only be observed by the human eye, which is why stained specimens can be observed under a regular microscope. And living cells and
Light waves have different amplitudes (brightness), wavelengths (color), and phases (referring to the positions that light waves can reach at a certain time). When light passes through an object, such as changes in wavelength and amplitude, it can only be observed by the human eye, which is why stained specimens can be observed under a regular microscope. Living cells and unstained biological specimens, due to slight differences in the refractive index and thickness of the microstructure of each part of the cell, do not change in wavelength and amplitude when light waves pass through, only in phase (the corresponding differences are called phase differences). However, these small changes cannot be distinguished by the human eye, so they are difficult to observe under ordinary microscopes. It can change the phase of direct or diffracted light, and use the diffraction and interference phenomena of light to convert phase difference into amplitude difference (brightness difference). At the same time, it also absorbs some direct light to increase the contrast between brightness and darkness. Therefore, it can be used to observe live cells or unstained specimens. The main differences between a phase contrast microscope and a regular microscope are: using a circular aperture instead of a variable aperture, using an objective lens with a phase plate (usually marked with PH) instead of a regular objective lens, and having a telescope for axis alignment. Circular aperture is a type of aperture formed by circular holes of different sizes, whose diameter and aperture width are matched with different objective lenses. Its function is to separate the image formed by direct light from some diffraction side images. The phase plate is installed at the rear focal plane of the objective lens, and is equipped with an absorption film that absorbs light and a phase film that delays the phase. In addition to delaying the phase of direct or diffracted light, it also has the function of absorbing light to change brightness. The adjustable axis telescope is used for uranium synthesis adjustment. When using a phase contrast microscope, the center of the circular f-shaped aperture under the condenser lens must be completely aligned with the optical axis of the objective lens. It is necessary to adjust the bright ring of the aperture and the circular ring of the phase plate to coincide and align in order to fully utilize the efficiency of the phase contrast microscope. Otherwise, the optical path of direct or diffracted light will be disrupted, and the light that should be absorbed cannot be absorbed. The light waves that should be delayed in phase cannot be delayed, and the effect of the phase contrast microscope will be lost.
