Focus lenses for laser engraving, marking and cutting

The right lens for perfect results.

Optimal results during laser engraving or laser cutting are achieved by using different lenses. This works in the same way as for a camera that uses different lenses for close-up and wide angle photographs. The various lenses differ by their respective focal distances. The focal distance is indicated in inches. This is the distance from the lens to the focus. The focus, in turn, is the smallest beam diameter (before and behind the focus, the beam expands again). A small beam diameter means a high energy density (= intensity), i. e. an 'aggressive' beam. A focal distance of 2 inches, for example, means that the maximum intensity is reached when the workpiece surface to be cut or engraved is positioned 2 inches (= 5.08 cm) underneath the lens.

How to choose the right focus lens.

The decision on what lens to use depends on a number of factors: laser power, type of material, degree of detail and resolution of the graphic (dpi), thickness of the material. The following rule of thumb can be applied: The greater the degree of detail of the graphic, the shorter the focal distance during laser engraving. The thicker the material during laser cutting, the greater the focal distance.

The following lenses are available for Trotec laser systems:

(⚪ = optional, ⚫ = standard)

Speedy series
SP series

Lens	100	100 fiber	100 flexx	300	300 fiber	300 flexx	360	360 fiber	360 flexx	400	400 flexx	500	1500	3000	Q400	Q500
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	⎯	⎯	⎯	⎯	⚪	⚪	⎯	⚪	⚪	⎯	⚪	⎯	⎯	⎯	⎯	⎯
7.5 inch CO₂	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⎯	⚪	⚪	⎯	⎯

The depth of field (focal tolerance), in turn, specifies the area in that the laser beam is optimally focused. The longer the focal distance, the longer the depth of field. This means that the depth of field of a 5 inch lens will be about twice as long as for a 2.5 inch lens. For this reason, the cutting edge of thicker materials will turn out straighter when a 5 inch lens is used than when a 2.5 inch lens is used. At the same time, the laser beam diameter will be greater the longer the focal distance is (for a 5.0 inch lens approx. twice as big as for a 2.5 inch lens). As a result, the energy of the laser (wattage) will be distributed onto a larger surface. Consequently, less power (here in the form of heat) per surface area will be applied. The use of a lens with a greater focal distance can therefore be advantageous for materials that react sensitively to heat (e. g. laminates). The greater focal diameter means a greater line width. Filling lines can therefore be cut with the laser at a greater distance and thus faster. The following table gives you a general overview of the various areas of use. However, you should adapt this information to your specific application.

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

Speedy series
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