Focal length is the distance from the center of the lens to the focal point of the lens.
Snapmaker designs both the Auto Focus and Manual Focus modes to help you measure the focal length. The measurement of focal length mainly involves the following procedures.
(1) Engrave a few lines at different heights.
Each laser engraving and cutting machine comes with a default focal length value, which is not always accurate. During auto focusing, the machine adjusts the height of the Laser Module based on the default focal length to engrave a series of lines on the material.
The manual focusing procedure does not necessarily use the default value for focal length. Instead, you can manually set a reference point. Then, the machine adjusts the height of the Laser Module based on the reference point to engrave a series of lines on the material.
(2) Identify the best engraved line.
At the optimal height, the laser is best focused and can engrave the thinnest line on the material surface, which is called the best engraved line. The lines engraved before or after the best engraved line should be thicker than it, as illustrated by the following figure.
(Line A is the best engraved line. Lines engraved before or after it are thicker.)
However, sometimes the engraving result does not contain the best engraved line. For example, Line B is the thinnest line in the following picture, but it is not the best engraved line. This is because the Laser Module did not reach the optimal height during the focusing procedure. In this case, the focusing procedure will fail. For more information about how to deal with failed focusing, see Laser calibration failed.
(3) Calculate and record the focal length.
After the best engraved line is identified, automatically or manually, the machine will register the corresponding laser height and calculate the focal length, which will be saved for subsequent use.
As long as you do not reassemble the Laser Module and the machine works normally, the recorded focal length can be used for the next engraving and cutting job. For the next engraving and cutting job in Auto Mode, you only need to set the material thickness, and then the machine will automatically adjust itself to ensure that the focal point always falls on the material surface.