How to Focus a Fiber Laser Lens and Calibrate It in LightBurn

A fiber laser’s beam is a precision tool. At its smallest spot, on the right material, you can make marks that read crisp at 10x magnification and stay legible after years of handling. Move the focus 2 mm above or below that point, and the same machine produces blurry edges, inconsistent depth, and burnt zones that drift across the workpiece.

This guide walks through the four operations that, together, lock a fiber laser into its rated performance: setting up a clean LightBurn device profile when you swap lenses, dialing in the exact focal height, correcting lens distortion with LightBurn’s Lens Calibration Wizard, and scaling the X and Y axes to a true 1:1 ratio.

The workflow applies to any galvo-class fiber laser running through LightBurn. Specific UI paths reference current LightBurn behavior on Windows; the same options exist on macOS and Linux with minor layout differences. If you are running a JPT M7 or M8 source on our 20W to 350W catalog, every step here is directly relevant. The motorized Z-axis included on every JPT machine makes the focal-height step measurably easier than on machines with a manual height crank.

Reading time: about 12 minutes. Plan 60 to 90 minutes the first time you walk a new lens through the whole sequence; 20 minutes for subsequent lens swaps once the workflow is in your muscle memory.

Why proper focus and calibration decide whether a fiber laser earns its price tag

A fiber laser source delivers a beam with very specific divergence and beam-quality characteristics. The Sino-Galvo SG7110 scanner head we ship across the JPT catalog deflects that beam with sub-microradian repeatability. The lens then focuses the beam onto your workpiece.

Each link in that chain is tight from the factory. The variable you control is the geometry between the lens and the workpiece: focal height, lens distortion correction, and the X/Y mapping that the controller uses to translate “draw a 50 mm line” into actual mirror angles.

Get all three right and the machine works at its rated specifications. Get any one wrong and the symptoms cascade. Out-of-focus marks read as soft, low-contrast, and wider than the design called for. Uncorrected lens distortion produces bowed sides on rectangles and skewed text on signage. Axis scale errors mean a part that needs to fit a 30 mm bezel arrives at 30.4 mm and gets rejected on QC.

Calibration is a one-time investment per lens. The payback is every production shift afterward.

What you need before you start

Every step below depends on accurate physical measurement. You cannot eyeball a 0.1 mm focal-height error or a 0.5 mm grid distortion. You need real tools that read in fractions of a millimeter. The kit is modest and covers every lens swap for the life of the machine.

Hardware:

• Digital calipers reading to 0.01 mm. The inexpensive ones are fine; what matters is repeatable measurement, not absolute traceability.
• A jeweler’s loupe at 10x or higher magnification. For finer work consider a 20x loupe.
• A USB digital microscope (optional, but transformative). The 200x to 1000x USB models that run under USD 50 give a clean view of burn edges that no naked eye can match. They plug into a laptop and show the image in real time.
• A fiber laser focus test tool. The pattern that works best is a small slanted block with calibrated graduations along the slope, so when you fire a continuous line across it you can read off the focal height from the thinnest part of the burn. You can buy one online or machine one from aluminum stock.

Materials:

• Plain-anodized aluminum business cards or small anodized aluminum coupons. The anodized finish reacts cleanly to a fiber beam, the cards are cheap, and they sit flat on the work surface without clamping.
• A few sheets of scrap stainless steel or coated metal for cross-checking once you have the focus dialed.

Software: LightBurn with the latest update applied. The Lens Calibration Wizard and axis-scaling options have moved between major versions; the steps below match current LightBurn.

The galvo machine itself: the motorized Z-axis on our JPT catalog moves the entire galvo head up and down on calibrated steps. On a machine with a manual rack-and-pinion or thumb-screw Z, the focus-finding steps still apply; you just measure the height with a height gauge or scale instead of reading it off the controller.

A clean, level work surface and consistent lighting for every calibration run will save hours over the long run.

Step 1: Set up a separate LightBurn device profile per lens

Every time you swap a lens on a galvo head, the optical system changes: the focal length, the working area, the calibrated grid, and the beam-divergence profile all shift. If you overwrite a working device profile in LightBurn with new lens settings, you lose the ability to swap back to the original lens without redoing every calibration step from scratch.

The fix is trivial: duplicate the existing device profile and rename it.

In LightBurn:

1. Open the device list (Edit > Devices, or the Devices button in the lower right of the screen).
2. Select your current working device profile.
3. Click “Export” and save the .lbdev file as a backup, labeled with the lens (for example, JPT-100W-110mm-lens.lbdev).
4. Click “Import” on a duplicate to bring in a fresh copy. Rename the new profile to reflect the new lens you are about to install, for example JPT-100W-300mm-lens.
5. Open the new profile, update the working-area dimensions to match the new lens, and save.

You now have two device profiles. The original is locked in with its proven calibration, and the new one is a clean slate ready for the focal-height and distortion-correction steps below. Toggle between them via the device dropdown any time you change lenses.

This habit pays off the first time you swap back. Instead of redoing 90 minutes of calibration, you select the saved profile from the dropdown and you are ready to mark in 30 seconds.

Step 2a: Find focal height on a known lens

The “known lens” case is the simpler of the two. Either the lens shipped with a published working distance, or you have used this lens on this machine before and you have a previous focal-height reading written down.

The verification method is what most operators call the “fire-and-listen” test:

1. Place an anodized aluminum card flat on the work surface, centered under the galvo head.
2. Lower the head to the published focal height (or your previous reading).
3. In LightBurn, set the laser to a low power, short pulse-on test. Typical values: 5 to 10 percent power, 20 to 50 kHz frequency, with the laser firing as a stationary point or a very short test mark.
4. Fire the laser. Listen for the loudest crackle and watch for the brightest spark. Note the height.
5. Raise the head 0.5 mm and fire again. Lower 0.5 mm below the original and fire again.
6. The height that produces the loudest, brightest, most concentrated spark is at or very near true focus.

For most fiber sources, true focus is the height where the energy density at the workpiece surface is highest. Higher density makes a louder acoustic event (you hear it) and a brighter visible plasma plume (you see it). Once you have it within 0.5 mm by ear and eye, you refine to within 0.05 mm with the calibration wizard in Step 3.

Write the verified focal height down. Tape it to the machine. Save it in the LightBurn device profile notes. You will need it every time you re-mount this lens.

Step 2b: Find focal height on a brand new lens

The harder case: you bought a new lens with a published working distance you do not yet trust, or the lens arrived without documentation. The published number is a starting point, not an answer. Real focal lengths drift slightly with mounting geometry, beam-divergence variation between sources, and the specific galvo head in use.

The fastest reliable method uses a focus test tool, sometimes called a “slanted block” or “focus ramp”:

1. Mount the focus test tool on the work surface. The slanted face should face up, with the lower edge nearest you and the upper edge farthest, or oriented sideways depending on the tool design.
2. In LightBurn, draw a continuous line across the entire slanted face. The line should cross the full range of heights on the slope.
3. Configure the line as a low-power fill or stroke, slow speed (around 100 to 200 mm/s), so the beam dwells long enough at each point to make a visible mark.
4. Fire the line.
5. The burn will be wider at both ends of the line where the beam was out of focus, and thinnest at the midpoint where the slope crossed the true focal plane.
6. Use the jeweler’s loupe or USB microscope to locate the exact thinnest point of the burn.
7. Measure the height on the slope at that point. The test tool’s calibrated graduations make this trivial; alternatively, measure with calipers from a known reference.
8. That height, relative to the bottom of the lens, is your true focal distance.

Update the LightBurn device profile with the verified focal height. Lock it in. Move on to Step 3.

If you do not have a focus test tool yet, you can improvise with a stack of business cards: mark a continuous line across the staircase, observe which step gave the thinnest burn, and measure that height. The slanted block is more precise; the staircase is the same idea executed cheaper.

Step 3: Run LightBurn’s Lens Calibration Wizard to correct distortion

Even a well-focused lens does not produce a perfect square. Galvo lenses, especially shorter or higher-magnification ones, introduce optical distortion across the working field. The two patterns to know are:

• Pincushion distortion: a commanded square engraves with sides that bow inward, like a tightly stretched fishing net. Common on shorter-focal-length lenses.
• Barrel distortion: a commanded square engraves with sides that bow outward, like a beer barrel. Common on some longer-focal-length lenses.

The cause is the same: light bends differently at the edges of the lens than at the center. Optical engineers can compensate with multi-element designs, but at the price points typical of field-replaceable galvo lenses, you correct distortion in software instead. LightBurn’s Lens Calibration Wizard is the tool.

The workflow:

1. In LightBurn, open Tools > Calibrate Camera Lens or Tools > Lens Distortion Correction. The exact menu path depends on your LightBurn version; if you cannot find it, search the Tools menu for “lens”.
2. The Wizard prompts you to burn a calibration grid. Accept the default grid unless you have a specific reason to change it.
3. Place an aluminum card flat on the work surface, centered under the head. Use a card large enough that the entire grid fits with margin.
4. Fire the grid at low power. The grid should be visible but not deep-burned. You are not engraving; you are marking enough to measure.
5. Remove the card. Lay it on a flat surface with bright, even lighting.
6. Use digital calipers to measure four critical distances: the total length of the top line, the total length of the bottom line, the total length of the left vertical line, and the total length of the right vertical line.
7. If the grid had no distortion, all four would equal the commanded length. In practice they differ by 0.5 to 3 percent on most lenses.
8. Enter each measured length into the Lens Calibration Wizard. The software computes the correction matrix and applies it as a per-axis scale curve baked into the device profile.

The next time you burn a square, it engraves with straight sides. Save the device profile. Document the measurements in a spreadsheet so you can detect drift over time.

Step 4: Calibrate the X and Y axis scale

Distortion correction handles bowing and skew. A separate problem is overall scale: when LightBurn commands a 50 mm line, does the burned line measure 50.00 mm, 49.50 mm, or 50.30 mm? This is the X/Y axis scaling step.

The scale error usually comes from manufacturing tolerance in the galvo head’s optical-to-mechanical mapping. The Sino-Galvo SG7110 head shipped on our JPT galvo catalog is rated to repeat positioning accuracy of less than 8 microradians, but absolute scale calibration is what determines whether a 50 mm command produces a 50 mm output.

The calibration:

1. In LightBurn, draw a vector line or rectangle with a precisely known dimension. A 50 mm by 50 mm square is the standard test shape.
2. Burn it onto an aluminum card at low power.
3. Use calipers to measure the actual width of the burned line.
4. If the measurement differs from 50 mm, you have a scale error.
5. Open the device profile and navigate to the X and Y axis settings (Edit > Device Settings > Scale, or similar depending on the LightBurn version).
6. Enter the measured value as the “actual” reading. LightBurn calculates the correction ratio and applies it to all future motions.
7. Burn a new 50 mm square to verify. It should now measure 50.00 mm within the limits of your calipers.

Do this for both the X and the Y axis. A common surprise: the two axes often have slightly different scale errors. Treat them as independent calibrations.

After this step, the device profile is locked in. A commanded design will burn at true scale, with straight edges, at the correct focal height.

Common mistakes that ruin marking quality

Most support questions about focus and calibration trace back to a small set of repeatable mistakes:

• Overwriting a working device profile instead of duplicating it. You lose the ability to swap lenses without re-calibrating.
• Calibrating at a height that is not the actual working height. If you calibrate the grid with a card on the work surface, then later place a thick workpiece on the surface, the calibrated focal plane is now 10 or 20 mm too high. Either calibrate at the height of your typical workpiece or re-focus per job.
• Reading focus by eye alone. The naked eye cannot reliably resolve the difference between a 0.05 mm and a 0.2 mm focal-height error. Use the microscope or jeweler’s loupe.
• Mixing up the X and Y axes when entering measurements. This produces calibrations that make the distortion worse, not better. Label every measurement and double-check the wizard inputs.
• Skipping the axis-scale step. Distortion correction does not fix overall scale. You can have a perfectly square engraving that is 1 percent too small in both dimensions.
• Burning calibration grids at high power. You only need to see the lines, not engrave them. Higher power produces wider burns that mask the true line position and skew the measurements.
• Calibrating on a warped surface. If the aluminum card is not flat, the “distortion” measurements are partly measuring the warp. Use a heavy flat backer or a thicker coupon.

Most of these are habits, not skills. Once you have walked through the full sequence twice, the right behavior locks in.

JPT-specific notes

A few details that matter on the JPT galvo catalog specifically:

Motorized Z-axis is standard. Every JPT galvo machine in our catalog ships with a motorized Z-axis included in the base price. The Z reads its position to fractions of a millimeter through the controller and EZCad, which makes the focal-height step significantly faster than on machines with a manual height crank. When you find true focus by the fire-and-listen test, you write the Z position down once and re-load it from a saved height profile every time you mount that lens.

Included lenses. Each JPT machine ships with two lenses of your choice, selected from a standard set (70 mm, 110 mm, 175 mm, 210 mm, 300 mm focal length). The 175 mm lens is the included default. If you ordered a different combination at checkout, that pair is what shipped. Document each lens separately in LightBurn (per Step 1); the focal height differs by tens of millimeters across the range. For a typical example of the included-lens package, see our 100W MOPA M7 fiber laser, which is the most popular tier and ships with the standard two-lens bundle.

M7 versus M8 source behavior. The M7 MOPA architecture and the M8 MOPA architecture have slightly different beam-quality profiles. M8 produces a tighter beam at very short pulse widths (down to 2 ns), which means the focus is more critical for short-pulse work like glass marking or ceramic micromachining. M7 is more forgiving at the same focal-height error because the typical pulse width is longer. If you are working on an M8 machine for short-pulse jobs (such as our entry-tier 20W M8 fiber laser), give the focus step extra attention. Detail on what separates M7 from M8 from E-series sources is in our JPT source grades explained pillar.

The Sino-Galvo SG7110 head specifications relevant to calibration: 10 mm aperture, plus-minus 11 degree scan angle, less than 8 microradian repeat positioning accuracy. The scan-angle limit determines the maximum working area for any given lens; that working area is what LightBurn needs in the device profile setting.

EZCad 2/3 alternative. If you prefer to calibrate inside EZCad rather than LightBurn, the same physical workflow applies (focal height by fire-and-listen, distortion correction via the EZCad Calibration menu, axis scaling via the X and Y scale fields). EZCad is included with every JPT machine; LightBurn is the third-party alternative many operators prefer.

FAQ

Calibrated laser, predictable marks

A fiber laser at true focus, with corrected lens distortion and scaled axes, produces marks that look the same on Monday morning as they do on Friday afternoon. The calibration is one-time work that pays back every production shift afterward.

If you are setting up a new JPT machine and want to talk through the calibration steps with a JPT specialist, email info@jpt-laser.com and we will walk through them with you on a call. If you are still selecting which fiber laser fits your work, our help me choose walkthrough narrows the catalog to two or three options based on your application.