Scan Lenses (F-theta) and Field Lenses

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In a laser marking or scanning system, two mirrors swing the beam across the work area and the scan lens focuses the spot on a flat plane, at every deflection angle, with the spot position proportional to the scan angle. That proportionality is the F-theta condition that names the lens family, and it is why a scan lens is a designed multi-element assembly rather than a simple focusing singlet. The manufacturer's lens device group documents this family under F Lens alongside beam expanders and telecentric lenses, and field lens — the same function under its other name — is one of the company's headline product lines.

The catalogue also carries a documented galvo mirror listing: an optical scanning galvo mirror for CO2 lasers. The scan lens and the galvo mirrors can be named against the same system description — wavelength, field size, spot requirement — in one enquiry, and the beam expanders page covers the element that sits before them to set the beam diameter.

Specifying a Scan Lens

• Laser wavelength — the lens is designed and coated for a band; CO2 and fibre/diode systems need different designs.
• Field size — the square or area the scanner must cover at the focal plane.
• Focal length / working distance — set by the machine geometry and the required spot.
• Entrance pupil — matched to the galvo mirrors and the expanded beam diameter.

Scan lenses are specification-led products: catalogue families exist, but the working part is chosen against the scanner it completes. Send the wavelength, field size and the galvo or scanner model if it is fixed, and the F-theta option is confirmed against them in the quotation. Minimums and pricing are confirmed per specification in the written quotation.

Frequently Asked Questions

What is an F-theta lens?

A scan lens designed so image height is proportional to the scan angle (f × theta), which keeps a galvanometer-scanned laser spot evenly spaced and focused across a flat field.

Do you supply the galvo mirrors as well?

A scanning galvo mirror for CO2 lasers is a documented listing. Whether it can be quoted together with a given scan lens is confirmed item by item in the enquiry.

Is 'field lens' the same product?

Field lens is the manufacturer's headline name for this lens family in scanning service; the F lens group in the lens device catalogue covers the same ground.

The Scan Lens as Part of a Scanner, Not a Shelf Item

A scan lens is not a camera lens, even though it can look like a finished product with a price. It behaves instead like the final element of a machine: its entrance pupil must sit where the galvo mirrors put it, its focal length sets the field size together with the scan angle the mirrors can deliver, and its design wavelength must match the laser or the focus simply is not where the drawing says. The documented family position is a grouping one: F lenses are catalogued in the same lens device group as the beam expanders, and the catalogue also carries a documented galvo mirror listing. Send that description — laser, wavelength, field, spot expectation, and any fixed machine geometry — and the quotation answers the system question rather than quoting a lens in the abstract.