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Resolving Power of Microscope

by Geoffrey Meyer, PhD

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    00:01 Leaving staining for a moment and just finishing, I just want to explain what resolving power means.

    00:09 You've been looking at histological sections in this lecture.

    00:14 I've shown you some electron micrographs in previous lectures and I just want to define what resolving power is.

    00:24 It's the ability of the microscope lens or an optical system to clearly distinguish 2 closely positioned objects.

    00:38 It depends on a number of factors.

    00:43 Resolution is a dependent on first of all, the wavelength of light or the wavelength of an electron beam, depending on whether you're using an electron microscope or a light microscope.

    00:57 And it also depends on what we call the numerical aperture or some details about the optics used in our microscopes.

    01:08 And I don't want to go into all the physics of numerical aperture and all the physics of resolution, but basically, if you look at the left-hand side, the minimum distance you can discern between 2 resolvable objects depends on the wavelength of light or the emission wavelength of an electron beam and also on the denominator, the numerical aperture.

    01:41 And quite clearly, you don't need to be a mathematician, but if you look at that equation, the smaller the wavelength is, the smaller the resolving distance is.

    01:56 So if you use a much smaller wavelength of light such as electron beam, then you're naturally going to resolve distances between 2 points that are very, very, very tiny or very closely related.

    02:14 The human eye has a resolving power of only about 0.2 mm or 200 µm.

    02:22 Lower than that, an object just appears as a single object.

    02:27 It doesn't appear as 2 separated individual separate objects.

    02:32 Light microscope gives us a resolution of about 0.2 µm, and the electron microscope, because it's got a much smaller wavelength that the electron beam gives us a lot better resolution of around 1 nm.

    02:51 So just finishing off.

    02:54 If we look at these 2 last sections, on the left-hand side is a light microscope picture or image taken through an epithelial surface in the gut.

    03:05 You've seen this before.

    03:07 You can see at the top along line of cells, they're columnar cells.

    03:14 They've got elongated nuclei which reflects the shape of the cells.

    03:20 And under the light microscope, you can just see at the very top the brush border, a very thin line on the surface of these enterocytes or these epithelial cells that represent microvilli.

    03:36 You can't see details of these microvilli because the resolving power is only 0.2 µm, using a standard light microsoft.

    03:48 If we use an electron microscope, our resolving power is a lot higher.

    03:54 We can resolve structures closer together and on the right-hand side, you now clearly see individual microvillus, collectively called microvilli, projecting from the cell surface.

    04:09 You can even see details of the glycocalyx on the surface.

    04:14 Fine detail, better resolving power, it's a product of the wavelength of either the light or the electron beam.

    04:25 And lastly, here is a picture of a piece of skeletal muscle on the left-hand side.

    04:32 Under the light microscope, you can just make out striations, but on the right-hand side, using an electron microscope, you not only see the striations, but you see them in more detail.

    04:47 In fact, you see details of the very dark and light bands that characterize the basic functional unit of skeletal muscle, and that is the sarcomere.


    About the Lecture

    The lecture Resolving Power of Microscope by Geoffrey Meyer, PhD is from the course Histological Techniques and Staining.


    Author of lecture Resolving Power of Microscope

     Geoffrey Meyer, PhD

    Geoffrey Meyer, PhD


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