Boss CO₂ (LS / HP series)
Lens focal length
2″ · 2.5″ · 4″
2.5″ does most jobs
Focal length trades detail against depth. A shorter focal length focuses to a smaller spot (finer engraving, clean thin cuts) but has a shallow depth of focus, so the material must be flat. A longer focal length holds focus deeper into the material (better thick cutting, more forgiving of uneven stock) but with a larger spot, so less engraving detail. Boss offers 2″, 2.5″, and 4″: the 2″ is for intricate engraving and thin cutting, the 2.5″ is the versatile do-everything most shops keep on, and the 4″ is for thick cutting.
1 · Why focal length changes everything
The depth of focus (focus tolerance) is the zone where the beam is at its smallest diameter — where it actually cuts and engraves cleanly. Two things move together with focal length:
- Spot size — a shorter focal length converges faster to a smaller spot → finer detail and higher energy density on thin material.
- Depth of focus — a longer focal length keeps the beam in tight focus over a greater depth → it can cut through thicker material and tolerate surfaces that aren’t perfectly flat.
You can’t have both at once — the smaller the spot, the shorter the depth it stays sharp. That single trade-off is the whole decision.
2 · The three Boss lenses, side by side
Thickness figures are from Boss’s lens guidance — they also vary with power and material, so treat them as starting points.
| Lens | Best for | Cuts up to | Engraving detail | Flatness needed |
|---|---|---|---|---|
| 2″ | Intricate engraving & thin cutting | ~¼″ | Best — smallest spot, finest detail | High — shallow depth of focus, material must be flat |
| 2.5″ (most used) | Versatile — balances engraving & cutting | ~½″ | Good | More forgiving than 2″ |
| 4″ | Thick cutting | Over ~½″ | Reduced — larger spot | Most forgiving of uneven stock |
3 · How to choose for your work
Detailed engraving or thin material → 2″
Awards, photo engraving, fine text, small inlays, and cutting thin stock up to about ¼″. You get superior resolution — just keep the material flat, because the depth of focus is shallow.
A bit of everything → 2.5″ (the default)
The most-used lens for a reason: good engraving detail and the ability to cut medium stock up to about ½″, forgiving of slightly uneven material. If you only keep one lens on the machine, this is it.
Cutting thick stock → 4″
For material over ~½″, the longer focal length keeps the beam in focus deeper for cleaner thick edges, and tolerates surfaces that aren’t perfectly flat. You trade away fine engraving detail to get there.
It’s the lens and the focus setting
Picking the right lens is only half of it — the lens still has to be focused correctly to the material surface, or you lose the spot quality you paid for. Setting focus is a separate step per material.
4 · Premium lenses: ZnSe & transmission
Beyond focal length, lens quality matters. Boss offers premium ZnSe (zinc selenide) lenses made in the USA that provide about a 14% improvement in transmission rate — more of the beam’s energy reaches the work instead of being lost in the optic, which helps cut speed and edge consistency, especially at higher duty.
Frequently asked
CO₂ lens selectionQHow do I choose the right focal length?
Match the lens to the job. Shorter focal length = smaller spot = finer detail but shallow focus (detailed engraving, thin cutting). Longer focal length = deeper focus = better thick cutting but a larger spot. For most shops the 2.5″ is the do-everything, 2″ for intricate/thin work, 4″ for thick cutting.
QWhat’s the difference between a 2″ and a 4″ lens?
The 2″ focuses to a smaller spot with shallow depth of focus — fine engraving and clean thin cuts up to ~¼″, but the material must be flat. The 4″ has a larger spot and deeper focus — cuts thick material over ~½″ and tolerates uneven surfaces, at the cost of engraving detail.
QWhich lens is best for engraving?
The 2″ — its shorter focal length gives the smallest spot for the finest detail. Keep the material flat (shallow depth of focus), and don’t expect it to cut thick stock well.
QWhat lenses does Boss offer?
Boss offers CO₂ lenses in 2″, 2.5″, and 4″ focal lengths, plus premium USA-made ZnSe lenses with ~14% better transmission.
5 · Related guides & next steps
- Beam Quality and M² — why focal length and spot size trade against each other.
- CO₂ Laser Air Assist guide — the other optics-saver: clean, dry air keeps this lens alive.
- Fiber Laser Power guide — when the job is metal instead of a CO₂ material.
- Setting focal depth on the LS series — the companion step once you’ve picked a lens.
- Cleaning & maintaining your CO₂ optics — keep the lens you chose performing.
Ready to match a machine to your work?
The right lens starts with the right CO₂ platform.
Lens choice is one decision on a well-built machine. Browse the Boss CO₂ lineup, or tell a specialist what you cut and engrave and we’ll point you to the right system and optics.