Structurally, phase contrast microscopes are different from ordinary optical microscopes in that:
1. The annular diaphragm has a diaphragm with a ring opening, which is installed between the light source and the condenser. The function is to make the light passing through the condenser form a hollow light cone and focus on the specimen.
2. Phase plate The phase contrast microscope adds a phase plate coated with magnesium fluoride inside the objective lens to delay the phase of direct light or diffracted light by 1/4λ. There are two regions on the phase plate, the part through which direct light passes is called "conjugate surface", and the part through which diffracted light passes is called "compensation surface". Phase plates are divided into two types according to their working effects:
(1) A+ phase plate: the direct light is delayed by 1/4λ, the light waves of the two sets of light waves are superimposed, and the amplitude is increased. The structure of the specimen is brighter than the surrounding medium, forming a bright contrast (or negative contrast).
(2) B+ phase plate: The diffracted light is delayed by 1/4λ, and the light waves of the two groups of light are subtracted after the axis is aligned, and the amplitude becomes smaller. The structure of the specimen is darker than the surrounding medium, forming a dark contrast (or positive contrast). The objective lens with a phase plate is called a phase contrast objective lens, which is often marked with "Ph" on the objective lens housing.
Axis Adjustable Telescope
The phase contrast microscope is equipped with a coaxial adjustment telescope (marked with the symbol "CT" on the housing), which is used to adjust the image of the annular diaphragm to completely coincide with the conjugate surface of the phase plate, so as to achieve special treatment of direct light and diffracted light .
When using, remove the eyepiece on one side, insert the coaxial adjustment telescope, and adjust the coaxial adjustment to adjust the focus of the telescope. There will be two rings in the field of view, which are the conjugate of the bright annular diaphragm ring and the darker phase plate. face ring. Then turn the two adjustment screws of the annular diaphragm on the condenser so that the two rings overlap completely. If the bright halo is too small or too large, you can adjust the up and down knob of the condenser to make the two rings fit perfectly. If the condenser has been raised to a high point or lowered to a low point and still cannot be corrected, the slide is too thick and should be replaced. After the adjustment is completed, the coaxial adjustment telescope can be removed, and the eyepiece can be replaced.
green filter
Used to adjust the wavelength of the light source. Different wavelengths of illumination light will cause phase changes. In order to obtain a good phase contrast effect, a phase contrast microscope requires the use of monochromatic light with a relatively narrow wavelength range, which is usually adjusted with a green filter.
The steps to use the phase contrast microscope are as follows:
① Select a suitable phase contrast objective lens according to the nature and requirements of the specimen to be inspected.
②Put the specimen slide on the stage and adjust the center of the optical axis.
③Use the coaxial adjustment telescope, adjust the ring diaphragm to completely overlap with the conjugate surface ring on the phase plate, and then replace the eyepiece. During the observation process, every time the multiple of the objective lens is changed, it is necessary to re-adjust the annular diaphragm to coincide with the ring of the conjugate surface of the phase plate.
④ Add a green filter and observe according to the operating steps of an ordinary optical microscope.
5 inverted microscope
The structure of the inverted microscope is basically the same as that of the ordinary microscope, except that the position of the objective lens and the illumination system are exchanged, the former is under the stage, and the latter is above the stage. It is mainly used to observe the cultured living cells and needs to be equipped with a phase contrast objective lens.
inverted biological microscope
6 polarizing microscope
Polarizing microscopy can be used to detect birefringent substances, such as chromosomes, collagen, filaments, etc.
Altec BK-POL Projection Polarizing Microscope
Altec BK-POL Transflective Polarizing Microscope
The difference from ordinary microscopes is:
①The light source of the polarizing microscope is equipped with a polarizer (polarizer), so that the light entering the microscope is polarized light.
② There is an analyzer in the lens barrel (analyzer, a polarizer whose polarization direction is perpendicular to the polarizer).
③ Use a rotating stage. When a single refraction substance is placed on the stage, no matter how the stage is rotated, no light can be seen in the microscope because the two polarizers are vertical, and when a birefringence substance is placed, since the light passes through this type The object is deflected when the object is rotated so that the object can be detected by rotating the stage.
④ Equipped with compensator or phase plate;
⑤Use a stress-free objective lens.
