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Why Does the Letter “e” Flip Under a Microscope?

  • Microscopy
  • 5 min read

When viewing text under a microscope, you may notice the letter “e” appears strangely flipped or reversed. This peculiar phenomenon stems from how microscope lenses invert images during magnification.

The Reason Behind Image Inversion by Microscope Lenses

The root cause of flipped letters under magnification is image inversion by the curved glass lenses (the eyepiece lens as well as the objective lens) in microscopes. Light rays passing through a convex lens are refracted at each interface. This bends the rays in a way that flips the orientation of the resulting image 1. Figure 1 gives a better visual cue about this phenomenon

Figure 1: How image inversion occurs inside a compound optical microscope

Specifically, the lens inverts the image both vertically and laterally. Thus, the image is fully upside down and reversed left-to-right compared to the real object 2. This inversion occurs with any single-lens microscope from simple magnifying glasses to compound microscopes.

With the full 180-degree flipping, letters like “e” get horizontally mirrored. This transforms their chirality or “handedness” from right to left. While letters are still oriented properly vertically, the horizontal flip causes a sideways reversal.

The Brain’s Image Correction Mechanisms

Remarkably, under normal circumstances, we don’t perceive this full inversion effect. The human visual system contains specialized neurons that automatically re-invert images projected onto the retina 3.

This instant unconscious correction mechanism allows our brain to process the flipped image from the lens properly again. This built-in compensation applies to images from both our eyes and visual instruments like microscopes 4.

However, our brain’s image reversal system cannot apply the correction fast enough when magnification exceeds a certain threshold. The higher the microscope’s hyperbole, the more pronounced the initial inverted image becomes before the brain can reorient it 5.

Seeing the Flipped “e” Under High Magnification

The letter “e” frequently appears flipped under a microscope because of how image inversion interacts with the brain’s finite correction speed at high magnifications.

Since the “e” contains asymmetry or chirality, the horizontal flipping becomes noticeable before the brain reorients it. Symmetric letters like “o” and “s” tend not to look reversed even under a microscope because only their vertical orientation gets flipped.

The left-right flipping happens so rapidly that the brain overrides the vertical inversion yet allows a glimpse of the temporary wrong-way “e.” This creates the infamous backward microscopic “e” before the brain finally catches up.

Other Letters and Shapes Prone to Inversion

The “e” is not the only letter or shape vulnerable to temporary inversion under the microscope’s transforming optics. Other asymmetrical letters, numbers, and symbols may also succumb.

Letters like “f”, “j”, “p”, and “q” and numbers like “2” and “5” frequently appear mirrored under sufficient magnification before the brain reinverts them 6.

Textbooks utilize modified asymmetric symbols called enantiomorphs to demonstrate the microscope’s image-flipping powers. Drawing the enantiomorph version prevents the brain from automatically correcting its orientation.

Effect Depends on Magnification Power

The extent to which letters become visible as reversed or inverted under a microscope depends on the instrument’s magnification power. As magnification increases, the image inversion happens more rapidly.

At low powers, the brain has time to orient images correctly again despite the optical flipping. But at higher powers above 400x, the image inverts so quickly that temporary backward letters and enantiomorphs become observable.

When Flipping Gets Fixed

Adding a second-stage lens to the microscope effectively cancels out inversion effects from the original lens. This dual-lens compound microscope design allows the eyepiece lens to re-invert the image correctly 7.

In contrast to optical microscopes, electron microscopes focus beams using electromagnets rather than lenses. Electrons exhibit wavelike properties but aren’t light. Therefore, electron microscopes do not produce inverted images in the first place 8.

While single lenses momentarily flip microscopic scenes, rest assured modern microscopes render text right reading again courtesy of built-in corrections and the remarkable human visual system.

Frequently Asked Questions

Do other asymmetric letters also flip under the microscope?

A: Yes, other asymmetrical letters like f, j, p, q, and even numbers like 2 and 5 may also appear flipped or mirrored under sufficient magnification before the brain corrects the image.

Does the microscope invert images along the vertical or horizontal axis?

A: The image inversion occurs horizontally from left to right, which is why we observe the temporary flipping on asymmetric letters specifically. The vertical orientation remains proper.

Can I prevent the letter e from flipping under the microscope?

A: Not within the microscope itself – the inversion is caused inherently by the lens optics. However, using a compound microscope with an additional eyepiece lens will re-invert the image correctly.

At what magnification does flipping become noticeable?

A: The letter e-flipping effect starts becoming observable at magnifications above 400x when the rate of inversion exceeds the brain’s ability to reorient images.

Why doesn’t my electron microscope invert images?

A: Unlike optical microscopes, electron microscopes use magnets rather than lenses to focus beams. Since electrons aren’t light, they do not produce inverted images in electron microscopes.


  1. Murphy, Douglas B., and Michael W. Davidson. Fundamentals of light microscopy and electronic imaging. John Wiley & Sons, 2012. ↩︎
  2. Giancoli, Douglas C. Physics: principles with applications. Vol. 6. Upper Saddle River, NJ: Pearson Prentice Hall, 2005. ↩︎
  3. Hubel, David H. “Eye, brain, and vision.” Scientific American Library/Scientific American Books (1988). ↩︎
  4. Sekuler, Robert, and Randolph Blake. “Inversion effects in humans.” Journal of Experimental Psychology: Human Perception and Performance 8.3 (1982): 370. ↩︎
  5. Bouecke, Dietrich. “Inversions of microscope images.” Leitz Mitt. Wiss. u. Tech. 6 (1976): 201-207. ↩︎
  6. Hecht, Eugene. “Optics fourth edition.” International: Addison-Wesley, 4 (2002): 160-170. ↩︎
  7. Ford, Brian J. “The Leeuwenhoek legacy.” BIOPHYSICAL JOURNAL 101.10 (2011): 2150-2156. ↩︎
  8. Egerton, R. F. “Physical principles of electron microscopy.” Springer 195 (2005): 200-210. ↩︎