CO2 Laser Lens Focus Length Explained

co2 laser focus length explained

The type of lens we use with a CO2 laser is optimized for the transmission of 10.6μm infrared wavelength. Light enters the lens and begins to converge to the focal point, after the focal point the light begins to diverge creating an hourglass profile. The rate and angle at which light converges and diverges depending on the focal length of the lens.
The shorter the focal length the faster the beam will converge & diverge also the focused spot size & depth of focus will be smaller. Depth of focus (DOF) is the usable range of the focused beam, anything outside of this value will begin to taper at an angle as the beam begins to diverge.
Short focal length lens will provide a smaller spot size but will have less tolerance to warped materials, also it will require greater accuracy to maintain the correct focus point.

The focal point is where the focused spot is at its smallest point, this is the point at which power density is its highest. This is what determines the possible resolution you can achieve with a specific lens.

lens-focus-length-image-explained

See the list below for a list of focal lengths and dpi's

  • F38.1mm - 334 DPI
  • F50.8mm - 200 DPI
  • F63.5mm - 142 DPI
  • F76.2mm - 102 DPI
  • F101mm - 84 DPI
  • F127mm - 75 DPI

To calculate the expected dpi achieved when using a focus lens use the following formula.

25.4mm (1Inch) / focus spot size = dpi

Examples

F38.1mm - 1.5 Inch Lens

Pros

  • Reduction in kerf on thin materials, great for high tolerance work such as inlays.
  • Shortest focal length allows for an additional 12.7mm of Z-axis height.
  • Highest resolution of all focal lengths.

Cons

  • Reduction in focal range due to the lens high divergence, this makes this type of lens unsuitable to warped or curved objects and materials.
  • Due to having a short focal length, the lens is in close proximity to the workpiece. This will cause greater exposure to contamination and will require an increase in air-assist pressure to keep the lens clean.
  • Not great at cutting thick materials 5mm thickness max.

 

laser-lens-focus-length-image

F38.1mm

  1. Focused spot size - 0.076mm
  2. Tolerance - +/- 1.905mm
  3. Focal Length - 38.1mm

F50.8mm - 2 Inch Lens

Pros

  • A great all-around lens, excellent at both cutting and engraving. The perfect balance.
  • Can cut up to 12.7mm thickness material.
  • Best focal length choice when both cutting and engraving.

Cons

  • Not the best lens for high-resolution engraving.
  • When cutting materials greater than 12.7mm in thickness the edge will become tapered due to the lens divergence profile.

laser-lens-focus-length-image

F50.8mm

  1. Focused spot size - 0.127mm
  2. Tolerance - +/-2.54mm
  3. Focal Length - 50.8mm

F63.5mm - 2.5 Inch Lens

Pros

  • Good for cutting materials up to 15.9mm in Thickness.
  • Greater focal tolerance makes this lens suitable for curved or warped materials.
  • Increased focal length creates an additional 12.7mm clearance over the 50.8mm focal length lens.

Cons

  • Larger focused beam spot reduces the resolution.
  • Not recommended for high-resolution photoengraving.
  • Reduces the available height of Z-axis by 12.7mm

laser-lens-focus-length-image

F63.5mm

  1. Focused spot size - 0.178mm
  2. Tolerance - +/-3.81mm
  3. Focal Length - 63.5mm

F76.2mm - 3 Inch Lens

Pros

  • Great at cutting up to 19.5mm thickness material.
  • great for cutting warped or complex materials.

Cons

  • Lower engraving quality, not suitable for photographs
  • Reduces Z axis by 25.4mm from the 50.8mm lens.

laser-lens-focus-length-image

F76.2mm

  1. Focused spot size - 0.25mm
  2. Tolerance - +/-4.25mm
  3. Focal Length - 76.2mm

F101mm - 4 Inch Lens

Pros

  • Great at cutting up to 25.4mm thickness material.
  • Great for cutting warped or complex materials.

Cons

  • Lower engraving quality, not suitable for photographs.
  • Reduces Z axis by 50.8mm from the 50.8mm lens.

laser-lens-focus-length-image

F101mm

  1. Focused spot size - 0.304mm
  2. Tolerance - +/-5.08mm
  3. Focal Length - 101mm

F127mm - 5 Inch Lens

Pros

  • Great at cutting up to 30mm thickness material.
  • Great for cutting warped or complex materials.

Cons

  • Lower engraving quality, not suitable for photographs
  • Reduces Z axis by 6.2mm from the 50.8mm lens.

laser-lens-focus-length-image

F127mm

  1. Focused spot size - 0.34mm
  2. Tolerance - +/-6.1mm
  3. Focal Length - 127mm

One thought on “CO2 Laser Lens Focus Length Explained

  • Alex Smith

    It’s really a nice and useful piece of info. I
    am glad that you just shared this useful information with
    us. Please stay us informed like this. Thank you for sharing.

    Reply

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