A bulk pack of ten 20mm zinc selenide lenses with a 3-inch focal length, aimed at shops that go through lenses quickly. LSYAMQF also sells a four-piece kit of one lens and three mirrors for a full optics refresh.
Most K40 owners buy one lens and a spare. This option is ten of them, all 20mm at 76.2mm focal length. That only makes sense if lenses are a consumable in your shop rather than an occasional repair.
Who fits that description? Makerspaces and school workshops, where many hands and little cleaning discipline cloud lenses fast. Small businesses running two or three CO2 machines on the same lens size. Anyone cutting smoky, resinous material daily with weak air assist.
The material is China PVD ZnSe, the budget grade of zinc selenide. Owners generally expect it to wear out sooner than CVD under hard use, which is the argument for buying in bulk. Buying ten PVD lenses is a different strategy from buying one CVD lens and babying it.
If you run a single hobby K40, a ten-pack mostly sits in a drawer. One CVD lens plus one spare suits that owner better, and there is less to store.
The pack is also a single focal length. If your machines need different focus depths, order each size separately rather than hoping one focal length suits every job. LSYAMQF offers the same lens from 38.1 to 101.6mm, and in 12, 18, 19.05 and 20mm diameters.
Diameter decides the head. At 20mm, these lenses need a head with a 20mm seat; a factory K40 head has room for nothing bigger than 12mm.
| Spec | Value |
|---|---|
| Lenses per pack (this option) | 10 |
| Diameter | 20mm |
| Focal length | 76.2mm |
| Focal length in inches | 3 in |
| Diameters offered | 12, 18, 19.05 and 20mm |
| Focal lengths offered | 38.1, 50.8, 63.5, 76.2 and 101.6mm |
| Material | PVD ZnSe, made in China |
| Coating | Double-sided coating |
| Laser type | CO2 engravers and cutters |
| Kit version contents | 1 lens + 3 mirrors (4 pieces) |
| Kit mirror material | Gold-plated silicon or molybdenum |
| Kit mirror diameter | 20mm or 25mm |
| Kit mirror thickness | 3mm |
| Kit lens diameters | 12, 18, 19.05 or 20mm |
At 76.2mm, these lenses focus an inch further from the head than the K40's standard 50.8mm lens. The spot is larger, roughly one and a half times the stock size for the same beam, and the band of good focus is deeper. That combination favours cutting through thicker material over fine engraving.
Deep focus helps a cut stay straight through the sheet. With a short lens, the beam spreads quickly below the focal point and the kerf widens toward the bottom. With a 3-inch lens it stays tighter for longer, which gives squarer edges on thick acrylic and plywood.
Do not expect the lens to add power, though. A K40-class tube sets the ceiling on how thick you can cut, and a longer lens only uses that power over a deeper band. The materials guide sets realistic thickness expectations.
For engraving, the larger spot softens small detail. A shop that both cuts and engraves often keeps a 2-inch or 1.5-inch lens for engraving work and a 3-inch lens for thick cutting.
An adjustable bed makes switching between focal lengths quick. The K40 upgrade guide explains where that fits among other improvements.
A ten-pack is only good value if the spares are still perfect when you need them. ZnSe coatings pick up moisture, dust and fingerprints if left loose. Store them like the precision parts they are.
Fitting follows the usual routine. Unplug the machine, wear gloves, handle the lens by its edge, and seat it curved face up toward the beam. Snug the retaining ring by hand; overtightening cracks thin lenses.
Frequent lens swaps chew up retaining rings if you use pliers.
Cleaning is the same two-step habit as any CO2 lens: loose dust off with air, then a single drag of solvent-wet tissue. When a lens shows brown spots or a crazed coating, retire it rather than cleaning harder.
Track how long each lens lasts. If lenses die fast, the cause is often smoke on the optics. Better air assist and exhaust can stretch a pack much further. The alignment guide also matters, because a beam clipping the lens edge overheats it.
LSYAMQF's second version is a different product: a four-piece kit of one lens and three mirrors. It replaces the whole optical path at once, which is often the smarter move on a K40 that has never had its optics refreshed.
The kit lets you pick the lens diameter and focal length and the mirror type and size. Mirrors come in gold-plated silicon or molybdenum, 20mm or 25mm, all 3mm thick. The option shown pairs three 25mm silicon mirrors with an 18mm lens at a long 127mm focal length, which is an unusual combination for a K40. Check every part of the option before ordering.
| Choice | Suits |
|---|---|
| 10-pack, 20mm, 76.2mm | Several machines or heavy cutting |
| Kit, 20mm mirrors | Stock K40 mounts plus an upgraded head |
| Kit, 25mm mirrors | K40s already on 25mm mounts |
| Single CVD lens | One machine, longest life per lens |
Against single lenses from other makers:
Whichever version you pick, confirm your head's lens seat and your mount size first. Owners still finding their feet should run through the K40 basics first.
Shops running several CO2 machines, makerspaces and schools, or anyone who cuts heavily and replaces lenses often. A single hobby K40 rarely needs more than a lens and a spare.
It focuses an inch further from the head than the standard 2-inch lens, with a larger spot and a deeper band of focus that favours thicker cutting.
No. They are 20mm across while the original K40 head is sized for 12mm, so a head with a 20mm seat comes first.
One lens and three mirrors. You choose the lens size and focal length, and mirrors in gold-plated silicon or molybdenum at 20mm or 25mm.
Sealed, in a closed box with a desiccant, labelled with diameter and focal length, and away from the machine's fumes.
