All about Phase Contrast Microscopes

Phosphatidylcholine liposomes using phase contrast microscopes
Source: Wikimedia Commons

Phase contrast microscopes use a special technique to view cells and cell components that would be difficult to see using an ordinary light microscope. Phase contrast is used to enhance the contrast of light microscopy images of transparent and colorless specimens. Let’s take a moment to learn all about phase contrast microscopes!

What are the uses of Phase Contrast Microscopes?

Phase contrast becomes especially useful when viewing transparent specimens, ideally when high-resolution is not required. Some use cases include living cells, microorganisms, thin tissue slices, fibers, and more. Phase contrast can even be used to view sub cellular particles, such as organelles.

How does it work?

Believe it or not, a traditional light microscope can be adapted for phase contrast microscopy without too many resources. A phase contrast condenser with a condenser annulus can be installed with a set of phase contrast objectives, each of which contains a phase plate.

These components translate small changes in the phase into changes in brightness. These are seen by the researchers as differences in image contrast, which helps otherwise transparent specimens appear easier to see.

But what do we mean by “phase?” Interestingly enough, some specimens do not absorb light, even if they are stained. These are known as “phase objects” because they slightly change the phase of light that is diffracted by them. The human eye cannot detect these changes, but the adaptations to a light microscope can! In fact, phase contrast microscopes can distinguish background light from light detracted by the specimen, and the result is a higher contrast image that allows the invisible to be seen.

Are there limitations?

While phase contrast microscopes can do amazing things, there are a few limitations. One more noticeable limitation is the “halo effect” that can appear in images. These halos are artifacts of the phase shifting methodology, and while they are not too much of an issue, they can make it hard to see the outer edges of an image. Furthermore, as stated earlier, phase contrast microscopes are not suited for applications where high resolution is needed. The resolution of phase images can be limited by the phase annuli limiting the numerical aperture of the system. Lastly, phase contrast isn’t ideal for very thick specimens as the light may be distorted too much and produce a poor quality image.

Stay tuned for more useful blogs from the Nuhsbaum team! Happy imaging!