How to Choose the Right Field Lens
How to Choose a Field Lens (Field Mirror)?
On laser marking systems, the field lens (often referred to as a “field mirror”) plays a major role in both mark quality and production efficiency.
Choosing the right field lens depends on multiple requirements, including your marking area, target engraving depth, required precision, and desired marking speed.
Below are the key ways a field lens can influence engraving and marking results:
- Marking area: The size of your workpiece determines the field lens size you need. As the marking area increases, the field lens typically uses a longer focal length. Because the column height on the machine is fixed, a longer focal length can change the maximum material height you can process comfortably.
- Focused spot size: In general, the longer the field lens focal length, the larger the focused spot diameter. A larger spot can reduce marking sharpness, especially for fine text, small graphics, or high-resolution work.
- Engraving depth: A longer focal length can reduce achievable engraving depth because a larger spot lowers energy density on the surface. If you need deeper engraving, a shorter focal length field lens is often the better choice.
- Marking precision: For high-precision applications, a shorter focal length field lens usually produces a smaller spot, which supports finer detail and cleaner edges.
- Power density: Focal length directly affects power density (power per unit area). With a longer focal length, power density drops, which may require higher laser power to reach the same engraving effect.
For this reason, if you plan to switch to a larger-area field lens, you should evaluate all of the factors above together rather than swapping lenses without a full setup review.
What Needs to Be Updated After Changing the Field Lens?
After replacing the field lens, you should complete the following steps:
Confirm the focal length: A larger marking area typically means a longer focal length. Set the correct focal distance based on the field lens specifications, and note the proper working distance so you can repeat it when processing materials of different thicknesses.
Update software settings: In your software, revise the working area, field lens parameters, and galvanometer settings to match the new optics.
Galvanometer settings should be verified using calibration software (Corfile2). You can reference the test video here:
https://youtu.be/llflAf0G62Q
Re-test marking performance: After the lens change, revalidate your marking parameters—such as speed, power, frequency, resolution, and other job settings—to dial in the correct results for your materials and applications.
