How Phase Contrast Microscope Works To Your Advantage
Have you ever heard of a phase contrast microscope? Probably you had, but you aren’t sure what it really is. This is how a phase contrast microscope works.
What Is Phase Contrast?
It was Frits Zernike who developed and used phase contrast method in microscopy. It was in the early part of the twentieth century. He discovered that you can create patterns of destructive interference over a light background if you improve the direct light path. The image details will look a lot darker than its lighter background because of such patterns. Zernike developed a ring system found in the condenser and the objective lens. This is to create those interference patterns.
If it is properly aligned, light waves coming from the illuminator will pass through your eye, but is out of phase for around half-inch of its wavelength. This will greatly improve the specimen’s image. Phase, however, works well for specimens that are transparent, colorless, and hard to identify from their surroundings. These specimens are called phase objects. Phase objects include bacteria, sperm tails, protozoans, as well as other kinds of unstained cells. The phase contrast technique was considered to be a great advancement in the field of microscopy, and it gave Zernike a Nobel Prize for Physics in 1953.
How to Set Up Phase Contrast Microscope
Let’s take, for example, a phase contrast kit being used on series microscopes (National Optical 160). It is made up of a centering telescope, 4 objective lenses, as well as phase condenser lens (Zernike).
To properly alignment the phase ring, you must engage the set screws. This can be accomplished by pushing in to the phase condenser those long adjustment screws. A thumb wheel can be found in the opposing side. You can use that to dial into proper setting so it will complement the power of microscope’s objective lens. The thumb wheel may include a BF setting, which will stand for brightfield. This permits you to make use of the phase objectives to conventional brightfield lenses.
You can’t expect for all phase contrast microscopes to be exactly the same, but the techniques used especially in setting them up are quite similar. Normally, the phase condenser can have 5 settings, which you can spin with your thumb. Their magnification falls on 10x, 40x, 20x, 100x, and the BF (or no phase).
So you can set the microscope suitable for phase optics, set the phase objective to BF and concentrate on the specimen at hand. To improve the quality of the image, adjust the condenser’s height. Subsequently, the condenser turret is set according to the setting of the selected lens and then you remove the specimen. The controls you see, which are sticking out from both sides at the back, are meant to center the condenser.
Remove one of the lenses of the eyepiece and attach the centering telescope in lieu of it. The set screw can be utilized to focus the microscope’s centering telescope. If you look into the telescope, you’ll observe two rings. They can either be concentric or not. If you turn the centering adjustment screws attached to the condenser, you can align the rings so they will be concentric.
Remove the attached centering telescope and put back the eyepiece lens. Place the specimen back on to the platform and you can now begin the phase observations. If you change the objectives, you need to perform the entire process again. The alignment, however, doesn’t change even if the objectives are modified.
Changing It to Darkfield
The phase contrast microscope can also function as a darkfield microscope. It happens when the condenser is set to another phase setting instead of the chosen lens. The effect is you have a lovely darkfield. Thus, you can have your own darkfield and phase contrast device. The specimen doesn’t appear like a phase image but more of an illuminated one against a dark background.
From Brightfield to Phase Contrast
You can add optical accessories for phase contrast to any conventional brightfield microscope. This can be used to create the contrast-enhancing effect for any transparent specimen. Those light waves being shifted and diffracted by phase objects can be transformed into amplitude differences by phase contrast so they become observable in eyepieces. Contemporary phase contract microscopes work so refined and efficiently that, together with electronic enhancement as well as post-acquisition image processing units, protein molecules or minute internal structures of specimens become visible.
Indeed, transparent specimens are no more. By understanding how phase contrast microscope works, you can definitely enhance cell observation techniques.
