The letter “e” looks inverted in a microscope because the objective lens turns the image around as it magnifies it. Light rays from the letter cross over as they pass through the objective, forming an image inside the microscope that is upside down and reversed left to right. The eyepiece magnifies that image again but doesn’t turn it back, so the “e” you see is rotated 180 degrees from how it sits on the slide.
For the lens optics in more depth, see our explainer on why microscope images are reversed and inverted. This page focuses on the letter “e” lab itself: how to do it, what you should see and why it’s set up the way it is.
Upside Down and Backwards, Not Mirrored
Lab worksheets often ask you to describe the “e” as seen through the microscope. The accurate answer is that it appears upside down and backwards, which together amount to a 180-degree rotation.
A useful way to check: a lowercase “e” rotated 180 degrees looks like the symbol “ə” (the schwa used in pronunciation guides). It does not look like a mirror-image “e” that reads backwards. If you turned the slide around on the stage by half a turn, the “e” in the eyepiece would look the right way up.
How to Do the Letter E Lab
You’ll need a compound microscope, a plain glass slide, a coverslip, a dropper of water and a lowercase “e” cut from a newspaper or other thin printed paper.
- Cut out a small “e.” Choose the smallest print you can find, and trim a small square of paper around it.
- Place it on the slide the right way up, as you would read it, with the letter facing you.
- Add a drop of water on top of the paper. This helps it lie flat and makes the paper a little more translucent, so light passes through more easily.
- Lower a coverslip at an angle, letting one edge touch the water first, then let it down gently to avoid trapping air bubbles.
- Put the slide on the stage with the “e” still facing you the right way up, centered over the light.
- Start on the lowest-power objective and focus using the coarse knob, then the fine knob. If you need a refresher, our guide on how to use a microscope properly covers the focusing routine.
- Compare and sketch. Draw the “e” as it looks on the slide and as it looks through the eyepiece.
A dry mount (paper on a slide without water or a coverslip) also works at low power, but the paper may curl and the image is usually less clear.
What You Should See
At 40x
With a 4x objective and 10x eyepiece, the letter is easy to recognize and usually fills a good part of the circular field of view. It appears upside down and reversed. You’ll also start to see that the “solid” black ink isn’t completely even.
At 100x and 400x
As you move up, you’ll see only part of the letter at a time because the field of view gets smaller. The paper turns out to be a tangle of fibers, and the ink sits on and between them in uneven patches. Depending on how the paper was printed, you might see tiny dots or speckles rather than solid ink. At 400x, the paper’s thickness means only one layer of fibers is sharp at a time, so try gently turning the fine focus to explore it.
What Happens When You Move the Slide
Most e labs also ask you to move the slide and note what the image does. You should find:
- Move the slide left, and the “e” moves right.
- Move the slide right, and the “e” moves left.
- Move the slide away from you, and the “e” moves toward you (down in the view).
- Move the slide toward you, and the “e” moves away from you (up in the view).
This is the same 180-degree rotation at work: every direction is swapped.
Why Use the Letter E?
The lowercase “e” is chosen because it looks different when it’s flipped top to bottom and when it’s flipped left to right. That makes the rotation obvious.
Many other letters wouldn’t show the effect well. Letters such as “s,” “z,” “o” and “x” look the same when rotated 180 degrees, so you couldn’t tell anything had happened. Letters like “n” become “u,” and “d” becomes “p,” which can look like a different letter rather than a rotated one. The “e” is also common, so it’s easy to find in small print.
Newspaper is used because it’s thin and fairly translucent, which lets light from below pass through it, and its small type fits well in the field of view at low power.
Common Questions From the E Lab
Does the eyepiece flip the image back? No. The objective forms the inverted image, and the eyepiece magnifies it without changing its orientation.
Do all microscopes show the “e” upside down? Standard compound microscopes do. Stereo (dissecting) microscopes contain prisms that re-erect the image, so an “e” would look the right way up. On digital microscopes it depends on the camera and software settings.
Why does the “e” look fuzzy at high power? At 400x you’re seeing the paper fibers and ink spread in detail, and the paper is thick compared with the very shallow depth of field. Only part of it can be in focus at once.
Why is it important to know about the inversion? Because you’ll be moving slides constantly. Knowing that the image moves opposite to the slide makes it much easier to find, center and follow specimens, especially living ones.
Once you’ve done the “e,” the same simple slide-making approach works for many other specimens. Our list of fun microscope activities has more ideas to try next.