Task #10

Phase Contrast Microscope Build

Why a phase contrast microscope?

We chose to make a phase contrast microscope because it can very efficiently visualize the images of the biological samples under its eyepiece. I want to obtain a career in the medical field, so being able to see biological samples with more detail under a phase contrast microscope compared to a normal microscope is fascinating. A phase contrast microscope is an optical microscopy technique that converts phase shifts in light passing through a transparent specimen to brightness changes in the image. 

How to build the phase contrast microscope?

We needed a light source, phase plate, condenser, and a few lenses.  The light source provides illumination for the specimen. The phase plate creates a phase shift in the light passing through it, which was crucial for generating contrast in the specimen. The condenser collects and focuses light onto the specimen to provide a bright and uniform illumination. The objective lenses are positioned close to the specimen and are responsible for magnifying the image. 

Where to put the lenses?

The first lens has a focal length of 24.5 cm, the second lens has a focal length of 75 cm, and the third lens has a focal length of 50 cm. Using the thin lens equation (1/do + 1/di = 1/f ), you can find the sample distance placement (24 cm) and the image plane placement (67.5 cm). We used a diagram to help map out where the lenses when and were the image should be produced. 

What is the magnification of this microscope?

ho = 0.34 cm​

hi = 4.8 cm​

Magnification = hi / ho  = 4.8 cm / 0.34 cm = 14.12 x

What difficulties did we face?

1. Aligning the microscope

   • Originally, the microscopes non-alignment came from us not having anything screwed into place. ​

   • After redoing the microscope and aligning everything, the only problem was with the light source moving (the clamp is not very stable). ​

2. The phase plate

   • It's not the right thing.

   • We don't know what it is. What we used as a phase plate ended up not being a phase plate, which is why we weren't seeing the effects of a phase plate. The box said it was a phase plate, but looked like it was just a clear piece of glass. 

   • What happened: ​

     • When we rotated our "waveplate", it did not change anything about the view of our cells. ​

   • What should have happened:​

     • When the waveplate is rotated, it changes the directional of the light, making light places dark and vice versa. This allows us to see different depths of the three dimensional cell. 

3. Obtaining parallel light

   • Calculations did not match measurements of microscope. ​

   • Needed parallel light for the lens equation to be effective. ​

   • Created parallel light by placing an iris in front of the ​light source, which blocked stray rays. 

What can we conclude from the phase contrast microscope build?

We can conclude that the phase plate microscope is particularly useful for observing live and unstained biological specimens, such as cells and tissues, where traditional microscopes may not provide sufficient contrast. ​We were able to see a living organism with our microscope build, which means it works correctly. 

Images of Build and Image Produced by Microscope