Quick answer: if your colour is drifting lighter, greyer, or shifting hue — say, a dark blue that's reading more like light blue — and none of your actual parameters have moved, focus is one of the first places to look. You don't need to chase a specific distance. Adjust your Z-height slightly, re-test on scrap, and watch how the colour responds.
Why focus affects colour at all
It's easy to think of focus as something that only matters for depth or edge sharpness — get it roughly right and move on. Colour marking is less forgiving of that assumption than plain engraving is.
Colour on stainless steel comes from a thin oxide layer building up on the surface, and how that layer forms depends heavily on power density — how much energy is landing in how small a spot. (We cover the mechanism itself in more depth in Part 1 of the stainless steel series.) When your lens is in focus, the beam is at its smallest, tightest spot, and your power density is at its highest for a given power setting. Move out of focus in either direction and that same power spreads over a larger spot — power density drops, even though nothing on your parameter panel changed.
A plain black engrave can often shrug this off and still look acceptable. Colour can't. The oxide layer that produces a rich, saturated colour needs that power density to be right, so a defocus that a black mark barely shows can visibly shift or wash out a colour pass.
What to actually watch for
Rather than working from a target distance, it's more useful — and more realistic — to work from what you see. A few patterns worth knowing:
Colour reading lighter than expected
The classic sign. A recipe that should give you a deep, saturated colour instead comes out closer to a pale or washed-out version of it — dark blue reading as light blue, deep red reading as a duller pink or orange. If your frequency, pulse width, speed, and power all match a verified recipe and you're still seeing this, focus is a strong candidate.
Colour shifting hue, not just fading
Sometimes it's less "faded" and more "wrong colour entirely" — the result lands in a different band of the colour chart than the one you were aiming at. Since colour bands on a chart are tied to specific frequency and pulse-width combinations at a specific power density, losing that density from defocus can nudge the result into neighbouring territory.
Inconsistent results across one piece
If colour looks right in one area of a job but flat or off in another, and your parameters were constant throughout, an uneven surface is the usual suspect — the workpiece isn't flat, or it's warped, and part of it has drifted out of your focus range while another part hasn't. This is common on curved parts, thin sheet stock, or anything that isn't sitting perfectly flush.
How to check and fix it — no gauge required
You don't need precision measuring equipment to work through this. A simple comparative test tells you what you need to know:
- Run your known-good recipe on a scrap piece at your current focus setting.
- Adjust Z-height a small amount — loosen or tighten slightly, whichever your setup allows — and run the exact same recipe again on a fresh spot.
- Repeat once more in the opposite direction from your starting point.
- Compare the three results side by side. The one that's most saturated and closest to your reference chart tells you which direction — and roughly how far — your current focus has drifted.
This is deliberately a comparison exercise rather than a measurement exercise. You're letting the colour itself tell you when you're close, instead of trying to hit an exact number that may not even transfer cleanly to your specific lens, machine, or focus tool.
Common causes of focus drift
If you've confirmed focus is the issue, it helps to know what's actually causing it to move around between jobs:
- Warped or uneven material — thin stainless sheet in particular can have a slight bow that puts part of the surface out of range even when the rest is fine.
- Inconsistent jig or spacer height — if you're using a physical focus spacer or jig, wear, debris, or an inconsistent placement habit can shift your effective height job to job.
- Material not seated flat — a piece that's tilted slightly on the bed, or that has debris underneath it, changes your working distance without you touching a single setting.
- Lens window fouling — dust, residue, or fine spatter on the protective lens window can subtly scatter the beam. Worth a visual check and a clean if colour has drifted gradually over many jobs rather than all at once.
Not sure if focus is your issue at all?
If you haven't ruled out the other usual causes yet, start with the full diagnostic — it walks through frequency, speed, power, focus, and surface prep in order.
Open the colour diagnosticFrequently asked questions
How far off does focus have to be before colour is affected?
There's no single number worth chasing — it depends on your lens, spot size, and the colour you're going for. Rather than dialling in a specific distance, watch the colour itself. If it's drifting lighter or shifting hue with your parameters unchanged, treat that as your signal to check focus, not a measurement to hit.
Do I need a focus gauge to check this properly?
It helps for consistency, but it isn't required. A focus gauge or cone mainly gives you a repeatable starting point between jobs. What actually matters is comparing a test result at your current focus against one slightly closer and slightly further, and watching how the colour responds.
Why does colour care about focus more than plain engraving does?
Colour comes from a thin oxide layer built up on the surface, and how that layer forms depends on power density at the surface. Defocus spreads the beam's energy over a larger spot, dropping that density even if your power and speed settings haven't moved — so colour shifts while a plain black mark can still look fine.