Focus Test

Tip

You can also use the Focus Test to try out different amounts of defocusing. Defocusing your laser produces thicker lines where it marks the material, which in turn allows you to increase the Line Interval setting on Fill layers, and speed up jobs.

The Focus Test generates and runs a test pattern to help you identify the optimal focal height for your laser.

Focal height affects the strength and size of the laser dot where it meets the material. A laser that is perfectly focused will have the strongest power output and smallest dot size possible.

The Focus Test pattern is made up of a user-specified number of lines, each engraved at a different Z axis height. Text is engraved beneath each line to indicate the Z height the line was engraved at.

Go to Laser Tools → Focus Test to open the Focus Test setup window, where you set the parameters used to generate the test pattern.

Preparation

Z Axis Control

In order to use the Focus Test, your laser must have a motorized Z axis that is controllable through LightBurn, and Z axis control must be enabled in your Device Settings.

You'll receive a warning message if Z axis control is not enabled in your Device Settings, and you attempt to open the Focus Test.

If you are not using Relative Z moves, you must set the Material height for the material you will be testing on in the Cuts / Layers Window, before opening the Focus Test. You'll need at least one object in your Workspace in order to adjust the Material height — any objects in your Workspace will be ignored when the Focus Test pattern is sent to your laser.

Material

You'll be engraving a test pattern onto a piece of material placed in your laser's bed. It's best to have the material loaded into your laser before opening the Focus Test, so you can set and check positioning.

Your laser's optimal focus doesn't depend on the type of material you're engraving on, but if you're purposely testing a range of defocused heights, you may need to run unique tests on each different material you work with to get the most accurate results.

Positioning

The Focus Test pattern will be output in your laser's work area according to the Start From mode and Job Origin you select before opening the Focus Test.

If you select Absolute Coords, the Focus Test pattern will be centered in your laser's work area.

Current Position and User Origin work exactly as they do for all other output.

See Coordinates and Job Origin for more information on these settings.

Focus Test Setup Window

GCodeDSP

Start Z determines the Z height of the first line in the Focus Test pattern.
End Z determines the height of the final line in the test pattern.

Note

If you are using Relative Z moves only, Start Z, End Z, and all Z heights tested in between are determined relative to the current Z position of your laser, at the time the test begins. In other words, the first line will be engraved at the laser's current Z position plus the value you enter in the Start Z field, and so on for all Z heights tested, until the End Z.

If you are not using Relative Z moves only, Start Z, End Z, and all Z heights tested in between are determined relative to the Material height you enter in the Cuts / Layers window before opening the Focus Test.
Steps determines the total number of lines to create in the test pattern. The total number of lines is equal to Steps + 1. The amount that Z height will advance between each step is equal to: (End Z - Start Z) / Steps.
Speed sets the speed at which your laser will engrave the lines.
Max Power sets the power at which your laser will engrave the lines.

Tip

Set Max Power just high enough to mark your material — if the power is set too high, the laser may char or cut through your material, making it challenging to determine which Z height was the optimal focal height.
Turn on High Power Laser Mode to enable Perforation Mode for the labels beneath each line, if they are overburning. Perforation Mode switches the laser off and on during cuts, reducing overall power output.
Preview shows a preview of the Focus Test pattern, as it will output to your laser.
Frame commands your laser to travel around the area the Focus Test pattern will be output to in your laser's work area.
Save GCode saves the test pattern in GCode format.
Start commands your laser to begin engraving the Focus Test pattern.
Press OK to save your Focus Test settings — saved settings will be present when you open the Focus Test later.
Press Cancel to discard any changes you've made to the Focus Test settings — settings will revert to previously saved settings when you open the Focus Test later.

The Focus Test setup window for DSP lasers

Start Z determines the Z height of the first line in the Focus Test pattern.
End Z determines the height of the final line in the test pattern.

Note

If you are using Relative Z moves only, Start Z, End Z, and all Z heights tested in between are determined relative to the current Z position of your laser, at the time the test begins. In other words, the first line will be engraved at the laser's current Z position plus the value you enter in the Start Z field, and so on for all Z heights tested, until the End Z.

If you are not using Relative Z moves only, Start Z, End Z, and all Z heights tested in between are determined relative to the Material height you enter in the Cuts / Layers window before opening the Focus Test.
Steps determines the total number of lines to create in the test pattern. The total number of lines is equal to Steps + 1. The amount that Z height will advance between each step is equal to: (End Z - Start Z) / Steps.
Speed sets the speed at which your laser will engrave the lines.
Max Power sets the power at which your laser will engrave the lines, once it reaches the Speed you've set.

Tip

Set Max Power just high enough to mark your material — if the power is set too high, the laser may char or cut through your material, making it challenging to determine which Z height was the optimal focal height.
Min Power sets the power at which your laser will begin engraving the lines. As the laser accelerates, power will increase until the laser reaches maximum Speed, and Max Power.

Turn on High Power Laser Mode to enable Perforation Mode for the labels beneath each line, if they are overburning. Perforation Mode switches the laser off and on during cuts, reducing overall power output.
Preview shows a preview of the Focus Test pattern, as it will output to your laser.
Frame commands your laser to travel around the area the Focus Test pattern will be output to in your laser's work area.
Save RD file saves the test pattern in RD file format.
Start commands your laser to begin engraving the Focus Test pattern.
Press OK to save your Focus Test settings — saved settings will be present when you open the Focus Test later.
Press Cancel to discard any changes you've made to the Focus Test settings — settings will revert to previously saved settings when you open the Focus Test later.

Interpreting Results

After engraving the test pattern, inspect the results.

The thinnest line in the engraving is the one that was run at the Z height closest to your laser's optimal focal height.

To dial in the optimal focal height further, you can re-run the Focus Test — select the two lines that look closest to ideal, and set Start Z and End Z to match their Z heights.

For more help using LightBurn, please visit our forum to talk with LightBurn staff and users, or email support.