How to select
the right lens for your application

Selecting the right lens can be the key to perfect laser results. Use the following guide to determine which lens you should use for your application.

Choosing the right lens can be tricky

The parameters are fine and the focus is set correctly, but somehow the engraving is not correct. Has this ever happened to you? This is most likely a lens issue. The correct lens is just as important as the right parameters and optimal focus adjustment.

To select the correct lens, you must consider the following:

Output of your laser device
Material
Detail level of the graphics
Resolution (dpi)
Thickness of the material

The rule of thumb:

The more delicate and detailed the graphics are, the smaller the lens should be chosen. For cutting thick materials, lenses of maximum size are recommended. For detailed information, please see the table below.

The Speedy and SP lens portfolio

The following table shows all the lenses available for the Speedy lasers and their applications.

Lens	When to use for engraving/marking	When to use for 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	Used mainly 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 flexx series. 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

Please note that not every lens is available for each device. We will be happy to assist you in selecting the ideal lens.

We will be pleased to advise you.

Technical features in plain terms

The following is a glossary of the terms used to discuss lenses.

Focal length

Distance between the lens and the point of the smallest beam diameter (= focus).

Focus

The area where the laser beam is optimally focused and converges to the smallest possible beam diameter.

Beam diameter

The diameter of the laser beam which becomes greater and greater before and behind the focus.

The longer the focal distance of the lens, the greater the beam diameter. The energy of the laser is focused by the lens onto a defined focal point. The greater the focal distance of the lens, the greater also the surface onto which the energy of the laser is applied. This may mean that if you use a large lens, the material is heated rather than cut.

Focus tolerance (depth of focus)

The area in which the beam has the smallest diameter.

The larger the lens (= the larger the focal length of the lens), the longer the focal tolerance. This means that the focus tolerance of a 5” lens will be twice that of a 2.5” lens. This is especially important if you want to cut through thick materials.

Engravers' Manual

We have compiled detailed information on the use of lenses in the Engravers’ Manual here.

Further information

Need more help?

Contact the Trotec service hotline where top qualified and motivated laser experts will assist you with any questions or problems.

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