Glossary · Setting

Focus (laser)

The point at which the lens focuses the laser beam most tightly. Only there is the beam small and strong enough for clean engravings and cuts.

Explained in more detail

The focal length is the distance between the lens and the focal point. For CO₂ lasers, lenses of 1.5, 2, 2.5 and 4 inches are common (38.1 to 101.6 mm), and 2 inches is regarded as the all-rounder. Short focal lengths produce a smaller spot for fine engraving but have a shallow depth of field, while long focal lengths have a larger spot and stay in focus over thicker material. Diode modules usually have a fixed lens, and the distance to the material is set with a distance gauge, by measurement or with autofocus. When cutting thick sheets, the focus is often placed slightly inside the material, frequently at about a third to a half of the thickness.

Where does the term come from?

Focus is Latin and means "hearth" or "fireplace". Johannes Kepler used the word for the point where a lens concentrates sunlight and makes it burn.

In practice

Use a ramp to find the focus: place a plate at an angle, engrave a line and measure the height at the thinnest point.
On gantry machines, it is measured from the top edge of the material, not from the support. If you change the material thickness, you must refocus.
Blurred, wide or faint lines are almost always a focus problem; only afterwards is it worth adjusting power and speed.
For curved or uneven parts, a longer focal length helps, because the beam stays sharp over a larger height range.

Not to be confused

Not to be confused with the focus of a camera in the laser, which is only responsible for the preview. Defocusing can also be intentional, for example for wider, softer lines.

Frequently asked questions

How do I set the focus on a diode laser?

Most machines have a distance gauge or an autofocus. Without either, a ramp test helps to find the distance with the finest line.

Where should the focus be when cutting?

With thin material, on the surface. With thicker sheets it often cuts better if the focus is moved a little into the material, for example to a third of the thickness.