Light Microscopy: Bright-Field Microscopes - Video Tutorials & Practice Problems

Light Microscopy: Bright-Field Microscopes

in this video, we're going to continue to talk about light microscopy by focusing specifically on the bright field microscopes. And so bright field microscopes are the most common type of light microscope that, as its name implies, is going to be generating a bright background. And so that's why it's called a bright field microscope because it generates a bright background. Now these bright field microscopes are going to be routinely used to examine both stained and unstained specimens to help form a darker image or darker objects on a lighter and brighter background. And so, if we take a look at our image down below over here, notice we're focusing in on bright field microscopy and so on. The left, notice that we have some cells undergoing mitosis that are going to be stained and recall that mitosis is division of the nucleus and eukaryotic cells. And so notice that these cells are going to be darker with respect to their background, which is lighter and brighter. And so this is what we call bright field microscopy. Now, on the right hand side over here, we're showing you some chloroplasts within some moss cells. Now, the chloroplasts are not actually staying here. The chloroplasts actually have this green appearance naturally. Uh and we'll be able to talk more about these chloroplasts later in our course. But ultimately I noticed that the cells are, the structures are going to be darker with respect to their lighter and brighter background. And so these are some examples of bright field microscopy. Now there is a drawback to bright field microscopy and that is that unstained transparent organisms sometimes can create really, really poor contrast with a bright background. And so if you have unstained transparent organisms, then they're not actually going to create a lot of contrast with their background. And so sometimes staining is not a solution to this because in some cases staining procedures may actually kill the organism and that may not be what the scientist is interested in. And so uh there are some other types of light microscopes that helped to resolve this drawback and help to increase the contrast. And so we'll be able to talk about light microscopes that increase contrast later in our course as we move forward. Now before we end this video, there is a very important type of bright field microscope called the compound light microscope. And the compound light microscope is one of the most commonly used bright field microscopes that is going to be using or calm pounding two lenses together. It uses an ocular lens along with an objective lens that are both going to help increase magnification. And so we'll be able to talk more about this compound light microscope later in our next video. But the compound light microscope is one that you're most likely going to use in your intro biology courses in your labs and in your microbiology labs and things of that nature. And so it is important to be familiar with the light compound like microscope, which again we'll talk more about in our next lesson video. But for now this year concludes our brief introduction to bright field mike the bright field microscopes, and we'll be able to apply these concepts as we move forward. So I'll see you all in our next video.

Components & Magnification of the Compound Light Microscope

In this video, we're going to talk about the components and the magnification of a compound light microscope. And so the compound light microscope actually has several different components, as you can see from down below in the image that you likely need to be familiar with. And so it's called a compound light microscope because there are two lenses that are compounded together, or two lenses that are used together. And so light is going to pass via two lenses, the objective lens and the ocular lens. And each of these lenses is going to provide additional magnification to help increase the apparent size of the image. And so if we take a look at this image that we have down below, notice that we're showing you the components of a compound light microscope and so notice that the compound light microscope is going to be compounding two lenses together. There's the ocular lens where these eyepieces are and then there's also the objective lenses, which are these lenses right here in this position and these lenses are rotate herbal lenses. You can actually rotate this little nose piece right here to get different objective lenses and each one provides different magnification. You can see the red one provides for X. Magnification. The yellow one provides 10 X magnification. The blue one provides 40 X. Magnification and usually there's 1/4 1 that's in the background that you can't really see right here, But it would provide 100 x. magnification. And so the objective lens with the ocular lens are compounded together and which is why we call this a compound light microscope. Then what we have here is the stage which is where you place your glass slide containing your specimen. And you have a slide holder here which is basically this little clip that's going to hold your slide in place so that it doesn't move around. You have a condenser right here at this position which is going to be focusing and controlling the amount of light. Then you have the light source at the very bottom. This is where the light is actually going to be originating from. Over here, you have a little level uh that you can use to control the intensity of the light. Then you have two knobs here that are referred to as the course focus and the fine focus. The larger one in the back, this larger piece here in the back is called the course focus. And the smaller knob right here is called the fine focus. And what these knobs do is they raise vertically and lower vertically the stage. And so the course focus is going to be quickly raising or lowering the stage vertically. Whereas the fine focus is going to be slowly raising or lowering the stage vertically. So they both do the same thing. It's just the speed at which they do it. The course focuses going too quickly move the stage and the fine focus will slowly raise the stage and this is all about helping to focus the image to make sure that the image is the specimen that you're trying to view is actually in focus and is as clear as it can be. And so really these are the main components of a compound light microscope. Now when it comes to determining the total magnification of the compound light microscope, what we need to know is that the total magnification of the specimen is going to be the multiplication. It's the multiplication of the magnification provided by each lens. And so usually when we're calculating the total microscope magnification we just multiply the ocular lens magnification by the objective lens magnification. And so the ocular lens magnification is usually always going to be 10 X. Magnification. And so the ocular lens magnification usually does not change. And that's fairly standard for the ocular lens magnification on a compound light microscope. Now the objective lens magnification can change and so it depends on which objective lenses being used. The red, the yellow, the blue or the black providing 100 X. And so if it were the four X. The red objective lens being used then to calculate the total magnification of the microscope, you just do 10 X times four X. And so 10 times four is 40 and the total magnification would be 40. If the four X were being used. Now if the 10 X objective lens were being used then you would do ocular lens magnification times 10 objective lens magnification. And so 10 times 10 is 100 X. And the total magnification would be 100 X. Now if the 40 X objective lens were being used then you would take the ocular lens magnification 10 X. And multiply it by 40 X. And so that would give you 400 X. Magnification and then last but not least if the 100 X. Objective lenses being used then to get the total microscope magnification you do the ocular lens magnification of 10 X times the 100 X. Of the objective lens. And so 10 times 100 is 1000 X. Magnification. And so be careful not to confuse total magnification with the magnification of each individual lens. And so it's important to remember that you need to always multiply the objective lens magnification by the 10 X. Ocular lens magnification to get the total microscope magnification. And so we'll be able to get some practice applying this concept right here as we move forward in our course. But for now, this year concludes our brief introduction to the components and magnification of a compound light microscope. So I'll see you all in our next video.

Light Microscopy: Bright-Field Microscopes Example 1

So here we have an example problem that wants us to complete the following diagram down below by labeling each part of the compound microscope. And so notice over here on the left hand side, we have a word bank with all of the components of the compound microscope. And we have to use this word bank to fill in all of these blanks, labeling each piece appropriately. And so I'm going to start at the very top here. And so what we have here are the two eyepieces where the ocular lens is found. And so what we can do is label this piece here as the ocular lens and then we can cross off ocular lens from our list. Next what we have here. It is labeling these objective lenses which recall our rotate herbal lenses that have different magnification. And so we can go ahead and label these as the objective lands or the objective lenses. And then go ahead and cross off objective lenses from our list. Next what we have here is the actual stage itself. This square, big square here is the stage, which is where the glass slide containing the specimen is going to be placed. And so we can label this here as the stage. Then uh next what we have here is this little clip right here, this little clip that is going to hook and hold the glass slide and place. And so this is what we call a slide holder because it holds the glass slide in place. Next what we have is this piece that's right below the stage here that we call the condenser, which is going to be important for focusing and controlling the amount of light that passes through so we can go ahead and cross off the condenser. Next, what we have here is the actual light source. And so we can go ahead and label this as the light itself. And so this is where the light will originate from. Then right here we have a knob that is going to be controlling the light intensity so we can label this as the light intensity control, light intensity control and then go ahead and cross off light intensity control from our list. Then over here we have two knobs. We have a larger knob in the back, and then we have a smaller knob here in the front. The larger knob in red is called the course focus, and the smaller knob is called the Fine focus. And so both of these knobs essentially do the same thing. They both will either raise or lower the stage vertically. The difference between them is the speed at which they raise and lower the stage. The course focus will raise and lower the stage much quickly, much more quickly because it's a larger knob, Then the fine focus is going to raise and lower the stage much slower. Uh And so um both of these knobs can be used by an experienced microscopic to help focus an image and focus the specimen under the microscope. And so this here concludes this example problem. And so now that we've labeled to find focused, of course, focus and the slide holder here, we can cross all of those off. And so we'll be able to get some more practice applying the concepts that we learned as we move forward, so I'll see you all in our next video.

What is the purpose of the condenser on a light microscope?

• A. Allows the viewer to change light intensity.
• B. Focuses the light beam and controls the amount of light hitting the specimen.
• C. Moves the microscope slide from left to right.
• D. Focuses the image magnified by the objective lens.
• E. Magnifies the microscopic specimen up to 100x.

What is the most common type of light microscope? And how does it work?

• A. Dark-field microscope; shows brightly lit specimens on a dark background.
• B. Light-field microscope; shows brightly lit specimens on a dark background.
• C. Bright-field microscope; shows a darker specimen on a brightly lit background.
• D. None of the above.

What is the major drawback to bright-field microscopes?

• A. Unstained microorganisms that are transparent are very difficult to see with bright-field microscopes.
• B. Bright-field microscopes cannot be used to examine stained microorganisms.
• C. The intensity of the light used to create the bright background in bright-field microscopes cannot be changed.
• D. Bright-field microscopes are some of the most expensive microscopes used to visualize microorganisms.

The knobs used for focusing the image on a compound light microscope are the:

• A. Fine & capture knobs.
• B. Course & tip knobs.
• C. Stage & course knobs.
• D. Course & fine knobs.

Which part of a compound microscope has the shutter that focuses & controls the amount of light?

• A. The condenser.
• B. The eyepiece.
• C. The stage.
• D. Fine adjustment knob.