Real vs Virtual Images in a Microscope, Explained Simply

The Short Answer

A compound microscope makes both kinds of image, one after the other:

• The objective lens forms a real image: magnified, inverted, and located inside the microscope tube near the bottom of the eyepiece. Light actually comes together there, so in principle it could be caught on a screen.
• The eyepiece takes that real image and forms a virtual image: further magnified and appearing to float some distance beyond the eyepiece. No light actually meets where it seems to be. You can only see it by looking into the eyepiece.

What you see when you look into a microscope is the virtual image. It’s still upside down and reversed compared with the specimen, because the eyepiece doesn’t undo the flip made by the objective.

Real and Virtual Images in Plain Terms

An image is formed when light rays from each point of an object are redirected, by a lens or mirror, so they come from (or appear to come from) a matching point somewhere else. Whether the image is real or virtual depends on whether the light rays really meet.

Real Images

A real image forms where light rays actually converge after passing through a lens or reflecting off a curved mirror. Because the light is physically there, you can put a screen, a sheet of paper or a camera sensor in that spot and the image will appear on it.

Everyday examples include:

• A projector throwing a picture onto a screen
• A camera lens focusing an image on its sensor
• The lens of your eye focusing an image on your retina

Real images formed by a single convex lens are inverted (upside down and reversed left to right).

Virtual Images

A virtual image forms where light rays only appear to come from. The rays leaving the lens or mirror are spreading apart. Your eye and brain trace them backward in straight lines and place the image at the point they seem to have come from. No light actually reaches that spot, so a screen placed there shows nothing.

Everyday examples include:

• Your reflection in a flat mirror, which appears to be behind the glass
• The enlarged text you see through a magnifying glass

A virtual image formed by a single lens or flat mirror is upright compared with the object it’s looking at.

Quick Comparison

Our explainer on how lenses magnify shows why the same convex lens can produce either kind, depending on how far away the object is.

The Microscope Uses Both

Stage 1: The Objective Makes a Real Image

The specimen sits just beyond the objective’s focal length. Under those conditions, a converging lens projects a real image that’s larger than the object and inverted. It’s the same thing a slide projector does, but on a much smaller scale.

In a microscope, this intermediate image forms inside the tube, at the plane of a fixed ring inside the eyepiece called the field stop. On microscopes with infinity-corrected objectives, the light leaving the objective is parallel, and an extra tube lens in the body brings it to focus to form the real image instead. Either way, a real intermediate image exists in the same place relative to the eyepiece.

Stage 2: The Eyepiece Makes a Virtual Image

The eyepiece is positioned so the intermediate image sits at, or just inside, its focal point. It then behaves like a magnifying glass looking at that image. Like any magnifying glass, it produces a virtual image: enlarged, and appearing farther away than the thing it’s looking at.

Your eye then does the final step. Its lens focuses the light coming out of the eyepiece onto your retina, making one more real image, the one your brain actually interprets.

So the full chain is: specimen → real image (objective) → virtual image (eyepiece) → real image on your retina (eye).

Our walkthrough of how a compound microscope works follows the light through each part, including the illuminator and condenser.

Why the Final Image Is Virtual but Still Upside Down

Students often learn the rule “real images are inverted, virtual images are upright.” That’s true for a single lens looking at an object. It causes confusion in a microscope, because the virtual image you see is upside down.

The answer is that “upright” means upright compared with whatever the lens is looking at. The eyepiece isn’t looking at the specimen. It’s looking at the objective’s real image, which is already inverted. The eyepiece’s virtual image is upright compared with that inverted image, so overall it stays inverted compared with the specimen.

That’s why a slide moved to the left makes the image move to the right in a compound microscope. Stereo microscopes and binoculars add prisms that turn the image the right way round, but most compound microscopes don’t.

Where Does the Virtual Image Appear?

Textbooks often say the eyepiece’s virtual image appears about 25 cm (10 inches) from the eye. That’s the standard “near point” distance used to calculate magnification, and it’s roughly where the image would sit if you focused as close as you comfortably could.

In practice, many people focus a microscope so the light leaving the eyepiece is close to parallel. Then the virtual image appears very far away, and the eye can stay relaxed, as if looking across a room. Either way, the image is virtual. It isn’t located anywhere you could touch or put a screen.

This is also why the focus position that looks sharp to one person may not look sharp to another. Each eye focuses the virtual image at a slightly different distance. The diopter adjustment on a binocular head lets you compensate for differences between your two eyes.

Seeing the Real Image for Yourself

You can often see the objective’s real image directly. On many microscopes, especially older finite-tube models:

1. Focus on a well-lit, high-contrast slide at low power, such as 4x or 10x.
2. Carefully remove the eyepiece. Cover the open tube when you’re done so dust doesn’t fall in.
3. Hold a small piece of tracing paper, frosted tape or thin white paper across the top of the tube, or slightly inside it.
4. Dim the room lights.

You may see a faint, small, upside-down version of the specimen on the paper. Move the paper up and down slightly to find where it’s sharpest. That’s a real image: the light really does come together there, and you’ve caught it on a screen.

Now try the same with the eyepiece in place and the paper held just above it. Instead of a picture, you’ll see only a small bright disc of light, the exit pupil. The eyepiece’s image is virtual, so there’s nothing to catch there.

How well this works depends on the microscope. On some designs the real image sits deep inside the tube, and the result can be dim. It’s still worth trying.

Why the Difference Matters in Practice

This isn’t just theory. Several practical features of microscopes depend on where the real image forms.

• Measuring reticles. A scale or crosshair placed at the eyepiece’s field stop sits in the same plane as the real intermediate image. That’s why the reticle and the specimen appear sharp at the same time.
• Microscope cameras. A camera sensor needs a real image. Camera adapters either place the sensor where a real image forms or use a relay lens to project one onto it. With the eyepiece’s virtual image, a camera has to use its own lens to form a real image, just as your eye does. That’s why holding a phone to the eyepiece works.
• Dust and debris. Anything lying in a plane that’s in focus with the specimen looks sharp. That includes dirt on the slide and specks on or very near the eyepiece’s field stop or reticle. Specks on most other lens surfaces are out of focus and tend to show up as soft blurs or slightly dimmer patches. If a speck turns when you rotate the eyepiece, it’s on the eyepiece.
• Glasses and focusing. Because what you see is a virtual image, you can usually refocus the microscope to suit your eyes. Many people with near- or long-sightedness can take their glasses off and simply adjust the focus. People with astigmatism usually need to keep their glasses on, which is easier with high-eyepoint eyepieces.

Common Misconceptions

• “A virtual image isn’t really there, so it’s less accurate.” A virtual image can be every bit as sharp and accurate as a real one. “Virtual” only describes where the light rays meet, not image quality.
• “Virtual images are always upright.” Only compared with whatever the lens is looking at. The microscope’s final virtual image is inverted relative to the specimen.
• “The microscope projects the image into your eye.” The eyepiece sends light into your eye, but your eye forms the final image itself, on the retina.
• “Real images are always smaller.” Not always. A camera photographing a landscape makes a small real image, but a microscope objective or a projector makes a larger one.

Frequently Asked Questions

Is the image in a microscope real or virtual? The image you see through the eyepiece is virtual. Inside the microscope, the objective first forms a real image, and the eyepiece magnifies that into the virtual image you look at.

Which lens in a microscope forms the real image? The objective. On infinity-corrected microscopes, the objective works together with a tube lens in the body to form it.

Why can’t you project a microscope image onto a wall with the eyepiece in place? In normal visual use the eyepiece makes a virtual image, so the light doesn’t converge to form a picture on a surface. If the focus is adjusted, an eyepiece can project a real image onto a screen or camera sensor held some distance above it, and some cameras and projection setups use this method.

Does a simple magnifying glass make a real or virtual image? When you use it normally, held close to the object, it makes an upright, enlarged virtual image. Our article on how a simple microscope works explains single-lens magnifiers in more depth.

For the wider basics, including the key terms used here, see our introduction to microscopy.