счмитьм. So, lets start the 1
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Good afternoon. It is good to see you all here. Let me just start by introducing myself. My name is Ekaterina Zinchenko. I am the 2nd year student of the Faculty of Physics. Today I am going to talk about Phase-contrast microscopy. In my presentation I will talk about Phase-contrast microscopy and its application in human life. I divided my presentation into three parts: use of phase-contrast microscopy, composition of phase-contrast device, setting up the phase-contrast. My presentation will take about 15 minutes a there will be time for questions after my presentation. So, let’s start the 1st part of my presentation. Microscopy of unstained microorganisms that differ from the environment only in terms of the refractive index does not change the light intensity (amplitude), and only the phase of the transmitted light waves changes. Therefore, the eye of these changes can not notice and the observed objects look low-contrast, transparent. For observation of such objects, phase-contrast microscopy is used, based on the transformation of invisible phase changes introduced by the object into amplitude, visible by the eye. This brings me to the end of my 1st part. The 2nd part is devoted to the composition of phase-contrast device. The phase-contrast device can be installed on any light microscope and consists of: a set of lenses with special phase plates; condenser with a rotating disk. Ring diaphragms are installed in it, corresponding to the phase plates in each of the lenses; auxiliary microscope. This brings me to the end of my 2nd part. In the 3rd part, I would like to talk about setting un the phase-contrast. The phase contrast setting basically consists of the following: replace the objectives and the microscope condenser with phase ones; install a small zoom lens. The hole in the condenser disk should be without an annular diaphragm; adjust the light according to Keller (Köhler); choose a phase lens of the appropriate magnification and focus it on the drug; turn the condenser disk and install an annular diaphragm corresponding to the lens; an eyepiece is removed from the tube and an auxiliary microscope is inserted in its place. Adjust it so that the phase plate (in the form of a dark ring) and the annular diaphragm (in the form of a light ring of the same diameter) are sharply visible. By means of adjusting screws on the condenser these rings are combined. Take out the auxiliary microscope and re-install the eyepiece. This brings me to the end of my 3rd part. In conclusion, I would like to talk about use phase-contrast microscopy. Phase contrast microscopy is also used to study tissue culture cells, observe the effect of various viruses on cells, etc. In these cases, biological microscopes with reverse optics are often used — so-called inverted microscopes. With such microscopes, the objectives are located below, and the condenser is above. For the invention of phase-contrast microscopy, the author of the Dutch physicist Zernike was awarded the Nobel Prize. That’s all I wanted to tell you, thank you for your attention. Now it’s time for your questions.
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