F-Theta Lenses and Marking Field Size
Shenzhen, China
Published: Jul 3, 2026
F-Theta Lenses and Marking Field Size
The F-theta lens is the unsung hero of galvo laser marking. It serves two critical functions:
How Field Size Works
The F-theta lens focal length determines the marking field:
| F-Theta Focal Length | Approximate Field Size | Typical Spot Size |
|---|---|---|
| 160 mm | 110 x 110 mm | ~50 μm (fiber) |
| 210 mm | 175 x 175 mm | ~70 μm (fiber) |
| 254 mm | 200 x 200 mm | ~80 μm (fiber) |
| 330 mm | 300 x 300 mm | ~100 μm (fiber) |
The tradeoff: Larger field size = larger spot size = slightly less detail. For most marking applications, the 175 x 175 mm field with a 210 mm F-theta lens is the optimal balance.
Telecentric vs. Non-Telecentric F-Theta Lenses
- Non-telecentric — Standard and most common. The beam angle varies slightly across the field, causing minor spot size variation. Fine for most marking applications.
- Telecentric — The beam always hits the workpiece perpendicular. More consistent spot size and marking quality across the entire field. Preferred for precision applications. Costs 2–3x more.
For electronics marking and other high-precision work, telecentric F-theta lenses are worth the investment.
