What does negative magnification mean?

A negative magnification means the image is inverted (upside-down) relative to the object. This is typical for real images formed on the opposite side of the lens from the object.

What is a virtual image?

When the image distance (di) is negative, the image is virtual — it appears on the same side as the object and cannot be projected on a screen. Magnifying glasses produce virtual images.

What units should I use?

Any consistent unit works (cm, mm, m). The magnification ratio is dimensionless, so only consistency matters — do not mix centimeters with meters.

What happens when the object is at the focal point?

When object distance equals focal length, the lens equation produces a division by zero, meaning the refracted rays are parallel and the image forms at infinity. This is how collimators work.

How is the thin lens equation derived?

It follows from Snell's law applied to a paraxial ray through a thin lens with two refracting surfaces. The result is 1/f = 1/do + 1/di, where distances are measured from the lens center.

Magnification Lens Calculator

Enter any two of object distance, image distance, or focal length to compute magnification and the missing variable.

Known Values

Enter any two of the three values. Leave the third blank to solve for it.

Solve for

Object Distance (d_o) — distance from object to lens

Image Distance (d_i) — negative = virtual image

Focal Length (f) — negative = diverging lens

Results

Enter values and click Calculate

Summary

Enter any two of object distance, image distance, or focal length to compute magnification and the missing variable.

How it works

Select which two values you know: object distance, image distance, or focal length.
Enter the known values in the input fields (in centimeters or millimeters).
The calculator applies the thin lens equation: 1/f = 1/do + 1/di.
Magnification is computed as m = −di / do.
Results show the missing variable, magnification magnitude, and image orientation.

Use cases

Verify the lateral magnification and image scale of an optical bench or projector setup.
Calculate image distance when object distance and focal length are known.
Determine if an image is real or virtual based on the sign of image distance.
Determine the magnification ratio and image size for macro or close-up lens setups.
Support optics coursework and lab preparation.
Cross-check microscope objective magnification for a given working distance.

Frequently Asked Questions

Last updated: 2026-09-13 · Reviewed by Nham Vu