Light Microscopes that Increase Contrast - Online Tutor, Practice Problems & Exam Prep

Light microscopy techniques enhance the visualization of unstained cells, addressing the limitations of bright field microscopy. Dark field microscopy presents bright specimens against a dark background, improving contrast significantly. Phase contrast microscopy utilizes special optics to make cellular structures appear darker against a grayish background, allowing for the observation of living cells without staining. Differential interference contrast (DIC) microscopy creates detailed, three-dimensional images with contrasting colors, further enhancing specimen visualization. These methods are essential for studying microorganisms and cellular structures effectively.

Light Microscopes that Increase Contrast

So now that we've introduced bright field microscopes, in this video we're going to talk about light microscopes that increase contrast. And so recall from our previous lesson videos that one of the drawbacks of bright field light microscopy is visualizing unstained transparent organisms. And that's due to really, really poor contrast that's associated with that. Now sometimes staining cells with dyes can help to increase contrast. And in those cases, the Brightfield light microscope can be used. However, sometimes these staining dyes can also kill cells or distort the features of those cells. And that may be something that the scientist is not interested in doing. And so in those cases, bright field light microscopy is not going to be the best solution. But thankfully, there are other special types of light microscopes that can help to improve contrast when visualizing unstained cells. And so some of these microscopes include dark field microscopes instead of bright field microscopes. Phase contrast microscopes, and DIC microscopes or Differential Interference Contrast microscopes. And so as we move forward in our course, we're going to talk a little bit about each of these 3 different types of light microscopes that increase contrast.

And so notice down below we have our map of the lesson or our outline of the lesson on light microscopy. And as we mentioned, we're going to be following this map by following the leftmost branches first. And so we've already talked about the bright field microscopes in our previous lesson video. So that part is done. With. Now we are moving on to the light microscopes that increase contrast, which once again includes dark field microscopes, phase contrast microscopes, and Differential Interference Contrast microscopes, or DIC microscopes. And so that's what we're going to be focusing on as we move forward. And then later after we finish those, we'll move on to the light microscopes that detect fluorescence, which are the ones that are over here. But for now, this here concludes our brief introduction to light microscopes that increase contrast. And once again, we'll talk about, the dark field microscope first, and then we'll move on to the phase contrast and DIC microscopes. So I'll see you all in our next video.

Dark-Field Microscopy

In this video, we're going to talk briefly about dark field microscopy. Dark field microscopy is essentially the opposite of bright field microscopy. Instead of observing a dark specimen against a light or bright background, dark field microscopy observes a bright specimen against a dark background. The term "dark field" refers to the dark background that's present. Dark field microscopes use a special mechanism that directs the light at a certain angle so that only light scattered by the specimen is observed.

Below, we're showing you some images of dark field microscopy, where the field refers to the background. Notice that all of these images show organisms that are brighter against a dark background. This is really the main idea of dark field microscopy: the dark background. We're displaying images of Volvox aureus algae, assorted diatom algae, Shigella dysenteriae bacteria, and Microsporum canis fungus, all against a dark background. Dark field microscopy can significantly improve the contrast, making it easy to distinguish the specimen from its background.

This concludes our brief introduction to dark field microscopy. We'll be able to apply some of these concepts as we move forward. I'll see you all in our next video.

What type of microscopy uses a special condenser that only allows light scattered by the specimen to reach the objective lens and causes the specimen to appear bright?

• A. Phase-contrast microscopy.
• B. Differential interference contrast (DIC) microscopy.
• C. Dark-field microscopy.

Phase-Contrast Microscopy

In this video, we're going to continue to talk about light microscopes that increase contrast by focusing briefly on phase contrast microscopy. Phase contrast microscopes are microscopes that make cells and their dead structures appear darker than the grayish background that they tend to create. In many phase contrast microscope images, you'll find that the background is going to be a grayish color and the cells and their dead structures will appear darker. However, there are some variations in these phase contrast microscopes that do not necessarily create gray backgrounds. That is not what defines the phase contrast microscopes. Instead, what defines these phase contrast microscopes is the complex special optic devices that they use, which are very complex and beyond the scope of this course. Really, what you can know about these special optic devices is that they increase the differences in how different substances and surroundings refract light differently. Different substances and surroundings refract light differently from each other naturally. However, those differences may be small sometimes. But these special optic devices can increase those differences to make the differences much larger between the two, and ultimately that can help to increase contrast. These phase contrast microscopes can be excellent for enhancing the contrast of internal details in unstained living cells. One of the advantages of the phase contrast microscopes is that there's usually no staining procedure required, and you are able to visualize living cells. Also, phase contrast microscopes can help to reveal cell structures that may not otherwise be able to be visualized using a normal brightfield microscope. These phase contrast microscopes do have advantages. So down below in our example, we're showing you some example images from a phase contrast microscope. With these phase contrast microscopy images, notice that many cases, the backgrounds are going to be grayish, and the cells and the cell structures will tend to appear darker. However, once again, there are some variations in these phase contrast microscopes, and they do not always create gray backgrounds. What classifies all these phase contrast microscopes together is the complex special optic devices that they use. But down below here, what we're showing you is an image from Mucor racemosus mold. Here, we're showing you an image from Cladophialophora bantiana fungus. Here, we're showing you an image of Pleurotus ostreatus fungus spores, and here we're showing you an image of Saccharomyces cerevisiae yeast. Ultimately, what you can take here from phase contrast microscopy is that it is one of the microscopes that's going to help increase contrast and be an alternative use to brightfield microscopes. This here concludes our brief introduction to phase contrast microscopy, and we'll be able to apply some of these concepts as we move forward. So I'll see you in our next video.

Differential Interference Contrast (DIC) Microscopy

In this video, we're going to talk briefly about differential interference contrast microscopes or DIC microscopes. DIC microscopes are going to create very detailed, highly contrasting, three-dimensional images of live specimens. In terms of the special optic devices that they use, those special optic devices are similar to the ones used in phase contrast microscopy. However, the main difference between the two is that the DIC microscopes add contrasting colors, and they create three-dimensional images. The three-dimensional images are really one of the biggest takeaways that you can take from these DIC microscopes. Notice that we have this three-dimensional cube shown here to remind you that the differential interference contrast microscopy, or DIC, microscopes will create these three-dimensional images. You can see that the images themselves do appear in somewhat of a third dimension. You can see, especially in this one here, how it appears to be coming off of the surface, and that seems to be the case in all of these images.

Here we have an image of Closterium algae, Penularidiata diatom algae, Paramecium caudatum, and Pediastrum algae over here. Once again, this microscope helps to increase contrast, allowing for very detailed, highly contrasting, three-dimensional images of live specimens. So, we'll be able to get some practice applying these concepts as we move forward in our course as well. So I'll see you all in our next video.

This form of microscope is able to refract light off of the dense structures of a cell making them appear brighter than the gray background.

• A. Phase-contrast microscope.
• B. Bright-field microscope.
• C. Differential interference contrast microscope.
• D. Dark-field microscope.

The microscope that increases contrast and allows the specimen to appear three-dimensional is the...

• A. Phase contrast microscope.
• B. Differential interference contrast microscope.
• C. Fluorescence microscope.
• D. Dark-field microscope.

Which of the following microscope types would be least useful in viewing unstained living cells?

• A. Phase-contrast microscope.
• B. Differential interference contrast microscope.
• C. Bright-field microscope.
• D. Dark-field microscope.

Which type of microscopes use light that hits the specimen indirectly, producing a darker image of the specimen on a brighter background?

• A. Phase-contrast microscope.
• B. Differential interference contrast microscope.
• C. Bright-field microscope.
• D. Dark-field microscope.

Here’s what students ask on this topic:

What are the advantages of dark field microscopy over bright field microscopy?

Dark field microscopy offers several advantages over bright field microscopy. The primary benefit is the enhanced contrast, which allows for the visualization of unstained, transparent specimens. In dark field microscopy, specimens appear bright against a dark background, making it easier to distinguish them from their surroundings. This technique is particularly useful for observing live microorganisms that might be killed or distorted by staining dyes. Additionally, dark field microscopy can reveal details that are not visible with bright field microscopy, making it a valuable tool for studying delicate or transparent samples.

How does phase contrast microscopy work to increase contrast in unstained cells?

Phase contrast microscopy increases contrast in unstained cells by using special optical devices that exploit differences in the refractive indices of cellular structures and their surroundings. These devices convert phase shifts in light passing through the specimen into changes in amplitude, which appear as variations in brightness. As a result, cellular structures appear darker against a grayish background, enhancing the visibility of internal details without the need for staining. This technique is particularly useful for observing live cells and their internal structures, which might be altered or destroyed by staining procedures.

What are the key features of differential interference contrast (DIC) microscopy?

Differential interference contrast (DIC) microscopy is known for creating highly detailed, three-dimensional images with enhanced contrast. The key features of DIC microscopy include the use of special optical devices similar to those in phase contrast microscopy, but with the addition of contrasting colors. This technique produces images that appear three-dimensional, providing a more detailed view of live specimens. DIC microscopy is particularly useful for studying the fine details of cellular structures and observing live cells in their natural state without the need for staining.

What types of specimens are best visualized using phase contrast microscopy?

Phase contrast microscopy is best suited for visualizing unstained, transparent specimens, particularly live cells and their internal structures. This technique is ideal for observing microorganisms, such as bacteria, yeast, and algae, as well as cellular components like organelles and cytoskeletal elements. Phase contrast microscopy enhances the contrast of these structures against a grayish background, making it easier to study their morphology and behavior without the need for staining, which can alter or damage the specimens.

How does dark field microscopy improve the visualization of transparent organisms?

Dark field microscopy improves the visualization of transparent organisms by using a special mechanism to direct light at an angle, so only light scattered by the specimen is observed. This results in a bright specimen against a dark background, significantly enhancing contrast. The dark background makes it easier to distinguish the transparent organism from its surroundings, allowing for detailed observation of its structure and behavior. This technique is particularly useful for studying live microorganisms that might be difficult to see with bright field microscopy.