FOCUS LENS 101

The laser beam for a CO2 laser engraver passes through a focus lens which narrows the beam to a sharp focal point in order to achieve all sorts of applications using the same laser equipment, from fine detailed engraving to cutting thick materials. This is a guide to help you choose the best lens for your application. Gravograph offers five different sizes of focus lenses.

All of our laser engravers come with a standard 2.0” focus lens which is a good general purpose lens. The available lenses are 1.5”, 2.0”, 2.5”, 3.5” and 4.0”. The smaller lens is better for detail while the larger the lens is better for cutting. The smaller focal distances require flatter material as the working range is more limited.

The focal length of the laser beam is a measure of how strongly it converges (focuses) or diverges (defocuses). As the laser beam passes through the focus lens is takes on an ‘hourglass’ shape,
whereas the ideal focal distance is at the center of this ‘hourglass’ (seen below). The longer focal lengths have a taller ‘hourglass’, thereby enabling you to reach the bottom of hollow objects without penetrating the object with the lens.

FOCUS LENS BENEFITS

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1.5 inch Focus Lens
Auto-focus probe clearance = 4mm to 5 mm (.157” to .197”)
Focused beam diameter = .13mm (.005”)
Typical processes = Ideal for cutting thin material (less than 1/16”) and fine single line images. Subject to beam splatter due to being so close to the part. Also great for high resolution raster engraving above 600DPI (dots per inch).
Great for = Laser colored foil, Gravoply Ultra, Gravoply Laser

2.0 inch Focus Lens
Auto-focus probe clearance = 5mm to 6mm (.197” to .236”)
Focused beam diameter = .18mm (.007”)
Typical processes = The best general purpose lens, good result on cutting and engraving. This lens comes standard on all Gravograph laser engraving systems.
Great for = Gravoxal, Gravotac, Colored Steel, Acrylic, Gravolase

2.5 inch Focus Lens
Auto-focus probe clearance = 36mm to 38mm (1.417” to 1.496”)
Focused beam diameter = .23mm (.009”)
Typical processes = Good power density for rubber stamps and engraving, also good for thin material cutting.
Great for = Rubber, objects with higher border or raised lip

3.5 inch focus lens
Auto-focus probe clearance = 35mm to 37mm (1.378” to 1.457”)
Focused beam diameter = .31mm (.012”)
Typical processes = Wide beam, makes it good for large area material removal and parts that require extra clearance.
Great for = Metallex, Gravotac

4.0 inch Focus Lens
Auto-focus probe clearance = 46mm to 48mm (1.811” to 1.890”)
Focused beam diameter = .36mm (.014”)
Typical processes = The best lens for thick material cutting.
Great for = Thick Acrylic, Gravoglas 1, objects with higher border or raised lip

The information covered in this technical tip are general guidelines. By using the proper lens for its intended application you can obtain exceptional results.