Focus lenses for laser engraving, marking and cutting

Precision focus lenses for Trotec laser systems

Optimal laser engraving and cutting depend on choosing the right lens with the appropriate focal distance.
Focal distance affects beam diameter and energy density, influencing cutting precision and heat dispersion.
Considerations for lens selection include laser power, material type, graphic detail, and material thickness.

Achieving perfection through lens selection

In laser engraving and laser cutting, striving for optimal results depends on choosing the right lens. This principle is similar to selecting different lenses for close-up and wide-angle shots on a camera. The key distinguishing factor among lenses lies in their respective focal distances, quantified in inches. Focal distance signifies the distance from the lens to the focal point – the point at which the laser beam achieves its smallest diameter before expanding again. A smaller beam diameter translates to higher energy density, creating a more “aggressive” beam. For instance, a 2-inch focal distance implies that maximum intensity occurs when the workpiece surface being cut or engraved is positioned 2 inches (approximately 5.08 cm) below the lens.

Choosing the ideal focus lens.

Determining the appropriate lens relies on a range of considerations: laser power, material type, graphic detail and resolution (dpi), and material thickness. Here's a rule of thumb to guide your selection: Greater graphic detail warrants a shorter focal distance for laser engraving, while thicker materials in laser cutting require a longer focal distance.
The following lenses are available for Trotec laser systems:

(⚪ = optional, ⚫ = standard)

Lens	100	100 fiber	100 flexx	300	300 fiber	300 flexx	360	360 fiber	360 flexx	400	400 flexx	500	R400	R500
1.5 inch CO₂	⚫	⎯	⚪	⚫	⎯	⚪	⚪	⎯	⚪	⚪	⚪	⎯	⎯	⎯
2.0 inch CO₂	⚪	⎯	⚪	⚪	⎯	⚪	⚫	⎯	⚪	⚫	⚪	⚫	⚫	⚫
2.0 inch CO₂ clearance lense	⎯	⎯	⎯	⎯	⎯	⎯	⚪	⎯	⎯	⎯	⎯	⎯	⎯	⎯
2.5 inch CO₂	⚪	⎯	⚪	⚪	⎯	⚪	⚪	⎯	⚪	⚪	⚪	⚪	⎯	⎯
2.5 inch CO₂ clearance lens	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⚪	⎯	⎯
2.85 inch flexx	⎯	⎯	⚫	⎯	⎯	⚫	⎯	⎯	⚫	⎯	⚫	⎯	⎯	⎯
3.2 inch fiber	⎯	⚫	⚪	⎯	⚫	⚪	⎯	⚫	⚪	⎯	⚪	⎯	⎯	⎯
3.75 inch CO₂	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⚪	⎯	⎯
4.0 inch CO₂	⎯	⎯	⎯	⚪	⎯	⚪	⚪	⎯	⚪	⚪	⚪	⎯	⚪	⚪
5.0 inch CO₂	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⚪	⎯	⎯
5.0 inch fiber	⎯	⎯	⎯	⎯	⚪	⚪	⎯	⚪	⚪	⎯	⚪	⎯	⎯	⎯

The depth of field, or focal tolerance, denotes the optimal focus area where the laser beam operates. Longer focal distances result in extended depth of field. Consequently, when using a 5-inch lens, the cut edge of thicker materials appears straighter compared to a 2.5-inch lens. However, a longer focal distance also means a larger laser beam diameter (approximately twice that of a 2.5-inch lens). This disperses the laser's energy (wattage) over a larger surface, reducing heat per unit area. A lens with a greater focal distance can be advantageous for materials sensitive to heat, such as laminates, due to the broader beam diameter.

This broader focal diameter also leads to a wider line width, facilitating quicker laser cutting of fill lines at a greater distance. The following table offers a general overview of lens applications, though we recommend customizing this information to suit your specific needs.

Lens	Area of use engraving / marking	Area of use cutting
1.5 inch CO₂	Graphics with fine detail, (resolution > 500 dpi), rubber stamps with thin letters	Lower laser power, thin materials (e. g. paper), acrylic < 6 mm, wood of medium hardness < 8 mm.
2.0 inch CO₂	Graphics with medium detail and resolution (resolution 500 dpi; with reduced definition up to a resolution of 100 dpi), standard engraving	Medium laser power, acrylic < 8 mm, wood of medium hardness < 12 mm.
2.0 inch CO₂ clearance lens	Mainly used for cutting	See 2.0 inch lens. Increases the distance between laser head and material. Is especially useful if the increased distance is required due to the material and the graphic
2.5 inch CO₂	Graphics with low detail, low resolution (< 500 dpi). Engraving on heat-sensitive materials (e. g. laminate) if large areas have to be removed completely.	High laser power, acrylic <12 mm, wood of medium hardness <15 mm Better quality of edges during laser cutting than for lower focal distances
2.5 inch CO₂ clearance lens	Mainly used for cutting.	See 2.5 inch lens. Increases the distance between laser head and material. Is especially useful if the increased distance is required due to the material and the graphic.
2.85 inch flexx	Standard lens for Speedy 300 flexx. Is transmissive for both CO₂ lasers and fiber lasers. Both laser sources can be used without changing the lens. Other characteristics as 2.5 inch CO₂ lens or 3.2 inch fiber lens	Characteristics as 2.5 inch CO₂ lens or 3.2 inch fiber lens
3.2 inch fiber	Standard lens for fiber lasers with extremely small focal diameter. Graphics with fine detail, ( > 500 dpi resolution)
3.75 inch CO₂	Lens for SP500 rotary engraving unit. Permits engraving of round objects with diameters of less than 50 mm
4.0 inch CO₂	Engraving by burning of wood, laser engraving of graphics with low detail with high laser powers	Foam rubber
5.0 inch CO₂	Is not used for laser engraving	High laser power, acrylic < 25 mm, wood of medium hardness < 20 mm Better quality of edges during laser cutting than for smaller focal distances
5.0 inch fiber	Lens for fiber lasers if materials that are not absolutely plane are to be labeled. The greater focal distance results in a greater tolerance during focusing.
7.5 inch CO₂ (for SP1500)	Is not used for laser engraving	High laser power, acrylic < 40 mm, Better quality of edges during laser cutting than for smaller focal distances