How does the ray diagram maker calculate image position?

The ray diagram maker uses 1/f = 1/u + 1/v to solve signed image distance and m = -v/u to calculate magnification. It then draws three paraxial principal rays that meet at the calculated image or extend backward to a virtual image.

What are the three principal rays in a ray diagram?

For a thin lens, the construction uses a parallel ray, an optical-center ray, and a focal ray. For a spherical mirror, this tool uses a parallel ray, a focal ray, and a center-of-curvature ray that reflects back along its incident line. Dashed backward extensions show where diverging rays appear to originate.

Can this ray diagram generator handle lenses and mirrors?

Yes. The ray diagram generator covers converging and diverging thin lenses plus concave and convex spherical mirrors. Each preset applies the correct focal-length sign and shows focal points on the appropriate side of the element.

When is an optical image real or virtual?

A positive image distance means the outgoing rays physically converge to a real image. A negative image distance means the rays diverge and only their backward extensions meet, so the image is virtual and is drawn with dashed extensions.

What happens when the object is at the focal point?

The image distance becomes unbounded when a real object is exactly at the focal point of a converging lens or concave mirror. The tool reports an image at infinity and draws finite, parallel outgoing rays instead of emitting invalid coordinates.

Is the ray diagram maker online and free to export?

Yes. This ray diagram maker online runs entirely in your browser, requires no account or credits, and exports SVG or PNG. The calculation is deterministic, but the thin-element paraxial approximation does not model aberrations, thick lenses, or multi-element systems.

Publication-ready scientific figures

Free Ray Diagram Maker

Name: SciFig
Author: SciFig

Calculate image distance and magnification, then draw three principal rays for converging or diverging lenses and concave or convex mirrors.

Free in-browser optics tool

Build a lens or mirror ray diagram

Choose one optical element, enter exact values, and verify the image with the Gaussian equation and three principal rays. No account or credits required.

Typical image cases

Optical element

Focal length magnitude

Object distance

Object height

Sign convention: converging elements use positive focal length; diverging elements use negative focal length. Positive image distance is real, negative is virtual.

Parallel ray
Central / C ray
Focal ray

Image distance v

Magnification m

-0.5

Image type

real

Orientation and size

inverted & reduced

The reduced, inverted, real image has magnification -0.5 and signed image distance 15.

Model: 1/f = 1/u + 1/v and m = -v/u under the paraxial thin-lens or spherical-mirror approximation. Dashed lines are backward extensions for virtual images. Display scale is clipped near the focal singularity; the numeric result remains exact.

3 principal rays · local calculation · no upload

What is a ray diagram?

A ray diagram maker calculates where an optical image forms and traces the principal rays that explain the result. This ray diagram generator supports a single converging lens, diverging lens, concave mirror, or convex mirror at a time. Enter focal length, object distance, and object height to solve the Gaussian equation locally, classify the image, and export an editable SVG or PNG without uploading data.

Ray Diagram Generator for Lenses and Mirrors

Four optical elements — switch between converging and diverging lenses or concave and convex mirrors without changing tools.
Exact numeric controls — combine sliders with precise focal length, object distance, and object height inputs.
Typical presets — compare objects beyond 2F, at 2F, inside F, and in front of diverging elements.
Immediate classification — the ray diagram generator reports real or virtual, upright or inverted, and magnified, equal, or reduced images.
Local calculation — the ray diagram maker online performs every equation in the browser with no upload or account.
Deterministic geometry — identical inputs always produce identical ray paths and image measurements.

Three Principal Rays for Every Optical Element

Parallel ray — enters parallel to the principal axis and refracts through, or appears to diverge from, a focal point.
Central ray — crosses a thin lens optical center without deviation; for mirrors, a ray along the center-of-curvature line reflects back along the same path.
Focal ray — passes through or aims toward a focal point and leaves parallel to the principal axis.
Principal axis — provides the signed reference line for object, element, focal points, and image.
Object and image arrows — show orientation and relative height directly from the calculated magnification.
Dashed extensions — distinguish a virtual image from solid rays that physically carry light.

Thin Lens and Mirror Equation, Signs, and Image Classification

Gaussian equation — 1/f = 1/u + 1/v determines signed image distance for the thin-element model.
Focal-length sign — converging lenses and concave mirrors are positive; diverging lenses and convex mirrors are negative.
Image-distance sign — positive v is real and negative v is virtual under the displayed convention.
Magnification — m = -v/u sets image height and indicates upright or inverted orientation.
Focal singularity — u = f sends the image to infinity, so the ray diagram software draws finite parallel rays and no image arrow.
Export — download the exact diagram as SVG for editing or PNG for worksheets, slides, and reports.