Resolving Power of Microscope

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.