Selecting the right lens for your application

What to Look for in a Lens

You've triple-checked your material processing parameters, and the laser's focus has been properly adjusted. However, your engraving results are of a lower quality than you expected.

Have you ever been in this situation?

The likely solution is to switch your laser's lens. As a matter of fact, the correct lens is just as important as the parameters and focus setting. The following factors should be considered when choosing a lens:

Laser power
Material type
Material thickness (when cutting)
Design resolution (dpi)

Two Rules of Thumb

Generally, the smaller and more detailed your design, the smaller your lens' focal diameter should be. For instance, we recommend using a 1.5" lens for engraving lettering on paper. On the other hand, thicker material cutting typically requires longer lens focal diameters to achieve clean results. An application example is cutting 1/2" acrylic using a 7" lens.

Speedy and SP Series Lenses

Lens	When to use for engraving/marking	When to use for cutting
1.5" CO₂	Graphics with high detail (> 500 dpi) Engraving small font to create rubber stamps	Lower-power cutting (e.g., paper, < 6 mm acrylic, < 8 mm wood)
2.0" CO₂	Graphics with moderately high detail (500 dpi; reduced definition up to a resolution of 100 dpi) Standard engraving with a Speedy system	Medium-power cutting (e.g., < 8 mm acrylic, < 12 mm wood)
2.0" CO₂ clearance lens	Used mainly for cutting	Increases the distance between the laser head and the material Useful if the increased distance is required due to the material and design
2.5" CO₂	Graphics with low resolution (< 500 dpi) Engraving large areas of heat-sensitive materials (e.g., laminates)	High-power cutting (e.g., <12 mm acrylic, <15 mm wood) Produces better edge quality during laser cutting (i.e., in comparison with lenses having shorter focal distances)
2.5" CO₂ clearance lens	Used mainly for cutting	Increases the distance between the laser head and the material Useful if the increased distance is required due to the material and design
2.85" flexx™	Speedy flexx™ standard lens Is transmissive for both CO₂ lasers and fiber lasers May be used in place of a 2.5" CO₂ lens or a 3.2" fibre lens	May be used in place of a 2.5" CO₂ lens or a 3.2" fibre lens
3.2" fibre	Standard lens for fibre lasers Graphics with high resolution (> 500 dpi) to be processed with a fibre laser
3.75" CO₂	Engraving with the SP500 rotary engraving attachment Engraving round objects with diameters > 50 mm
4.0" CO₂	Engraving wood creates scorch marks Engraving of low-detail graphics with high-power lasers	Rubber cutting
5.0" CO₂	Not used for laser engraving	High-power cutting (e.g,< 25 mm acrylic, < 20 mm wood) Produces better edge quality during laser cutting (i.e., in comparison with lenses having shorter focal distances)
5.0" fibre	Marking materials that are not absolutely flat Greater focal distance results in a higher tolerance* during focusing * see section below
7.5" CO₂ (for SP1500)	Not used for laser engraving	High-power cutting (e.g., < 40 mm acrylic) Produces better edge quality during laser cutting (i.e., in comparison with lenses having shorter focal distances)

Lens Lingo

The following are a few terms that are often used to describe laser lens characteristics.

Focal Length
The focal length is the the distance between the lens and the point of the laser beam having the smallest diameter (i.e., the focus).

Focus Plane (Focus)
The focus plane, or simply the focus, is the area where the laser beam converges to the smallest possible beam diameter.

Beam Diameter
A laser beam doesn't have the same diameter across its entire length. Instead, the diameter of a beam becomes increasingly larger before and behind the focus plane.

The energy of a laser is channeled by the lens to a defined point. The greater the focal length 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, your material may be heated rather than cut.

Focal Depth (Focus Tolerance)
A lens' focal depth, or focus tolerance, is the stretch of the beam having the smallest diameter. A larger lens has a longer focal length. In turn this means that the lens has a longer focus tolerance. For instance, the focus tolerance of a 5” lens will be exponentially larger than that of a 2.5” lens. This fact is especially important if you want to cut through thick materials.

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