Let’s Take a Closer Look at Microscopes!

The ocean is filled with critters we can’t see with the naked eye. Microscopes are an essential tool for learning how organisms develop, identifying diseases, how pollution travels through food webs, and what life exists below our range of vision. Microscopes have revolutionized how we study marine science and there are more to them than meets the eye.

Compound light microscopes in the CIMI Plankton Labs let us see into a smaller, thriving world. 

Photo credit: Alyssa Bjorkquist

Microscopes (“micro” = small, “scope” = to look at) come in different styles depending on how small of an organism a scientist intends to observe. Our student marine scientists at CIMI use compound light microscopes. These microscopes allow us to see plankton at 250 times greater magnification than plain sight! Although plankton—drifting animals—can weigh in at a whopping 5000 pounds (Mola mola, Ocean sunfish), a vast world of marine creatures are so small that they can only be observed with a microscope.

Parts of the Compound Light Microscope

Photo credit: Pinterest

Microscopes look complicated, but their anatomy is simple enough to navigate. Once the microscopes are plugged in and turned on, a light illuminates the subject through a diaphragm to create a bright field of viewing. An eyepiece is connected to a rotating set of objective lenses. The eyepiece has a set magnification, but various high- and low-power objective lenses can be clicked into place to view organisms at different magnifications. The lenses point to a stage containing a glass slide with organisms of interest. These three main sections—the lenses, light, and stage—are all connected by a sturdy arm. Four knobs assist scientists in making microscopic observations. The coarse knob moves the entire stage up and down, cutting through different layers in the sample to focus the main image in the eyepiece. The fine knob can make minute focusing adjustments to see different layers of an organism. Finally, translational knobs move the slide left, right, up, or down in the bright field so one can explore everything in the sample.

It only takes a few minutes to prepare a microscope for use! Simply turn on the microscope, put a drop or two of freshly filtered seawater from a plankton tow onto a glass slide, then insert the slide into the stage. With both eyes open, look through the eyepiece and focus carefully using the coarse adjustment knob. Once a subject is centered in your field of vision with the directional knobs, you can adjust the fine focus knob to explore the organism at the current magnification or switch to a more intense objective lens for closer magnification.

Left: Squinting with one eye is an efficient and harmful way to look into a microscope.
Right: Having both eyes open, but covering the unused eye, is a professional and safe method!
Photo credit: Alyssa Bjorkquist

Once you become more familiar with microscopes you can improve upon your observation skills. For example, professional biologists that look at microscopes for hours on end avoid eye strain and fatigue by using both of their eyes to view an image. Instead of squinting and using only one eye like introductory scientists, they train to keep both of their eyes open even when using a microscope with only one eyepiece. Practice using both of your eyes by covering the eye not looking through the eyepiece with one of your hands. With practice, you can observe countless organisms like a professional marine scientist!

To learn how to make your own microscope at home for $5, follow this link:
To learn about microscopes are being made accessible to millions, watch this inspiring TED talk:
To explore microscopes in a fun, interactive activity check out this lab:
Follow this link for a virtual biology microscope lab:
If you have access to a microscope, check out this website for different things to look at:


  1. Microscope anatomy:


  1. Introduction to Compound Microscopes:
  2. History of the Microscope:
  3. Compound Microscope Accessibility: