Why a 14mm M12 Lens Is Hard to Find in Any Catalogue

A 14mm M12 lens is a reasonable thing to write in a project brief and a difficult thing to buy. In this focal band, the number on the brief and the way a lens range is organised do not line up, and the gap is short enough to explain in one page of geometry.

Focal length is a result, not an input. A lens is chosen so that a given sensor projects the required field at the working distance the machine can actually provide, and magnification is the working distance divided by the focal length. A lens family is therefore tooled around the standoffs its customers build, which is why the long focal length M12 band is a series of named parts rather than a continuous scale: 9.04mm, 9.3mm, 10mm, 10.36mm, 10.9mm, 11.08mm, 13mm, 16mm, 16.1mm, 17.8mm and 20mm. The 13.0mm and 16.0mm parts leave a three millimetre opening, and 14.0mm sits inside it.

That opening matters less than it first appears. Field width scales in direct proportion to focal length, so moving 13.0mm to 14.0mm widens the field by about seven percent, and a standoff adjustment delivers the same change without a new part. Anything wider than seven percent is a different conversation, and it is a design review rather than an order line.

The two ways a drawing can say "14mm"

The second reason these requests take time is that a bare figure carries no unit of meaning. Both readings below are common, and they generate different shortlists, so the question to settle first is where the number came from.

• 14mm as focal length (EFL). The figure comes from a field of view calculation. No standard part sits on 14.0mm; the neighbours at 13.0mm and 16.1mm usually close the application once the standoff is confirmed.

• φ14mm as barrel outside diameter. The figure comes from a mechanical envelope drawing, and the focal length is whatever the application needs. In the M12 range this is a common barrel size that appears across many parts, most of the wide angle band from 2.0mm to 8.0mm included, while a 14.0mm focal length appears in none of them.

A catalogue filtered on "14mm focal length" returns nothing, and that absence is easily read as a gap in the range. Filtered on a φ14mm barrel outside diameter, the same range returns a long list. Which list is the right one is decided by a single question about the source of the number, and asking it first is cheaper than a sample evaluation that measures the wrong thing.

Reading the Numbers for a Robot Instead of a Camera

Robotic vision adds two constraints that a camera-only specification tends not to capture: the working distance is fixed by the machine, and the field has to keep its shape after the arm has moved ten thousand times. Both are settled by figures that appear on the lens drawing.

Working distance and field are one decision, not two

Take a 1/2.7 inch sensor with a 5.57mm by 3.13mm active area. At an 85mm working distance, a 13.0mm lens projects a field of roughly 36.6mm by 20.6mm. Move the same lens to a 50mm standoff and the field narrows by about forty percent, to roughly 21mm of width. Nothing about the lens changed; the magnification did. It follows that a requirement written as "a 14mm lens" without a working distance cannot be checked by anyone, while a requirement carrying both can be verified in one line of arithmetic.

Depth of field is where focus becomes a mechanical item

At F3.0 and a standoff measured in tens of millimetres, usable depth of field runs only a few millimetres deep. That is workable, and it is narrow enough that focus position stops being a setting and becomes a tolerance on the drawing. Three arrangements cover most projects:

1. A fixed focus build with a hard stop. The simplest option, and the right one when the incoming housing tolerance and the mounting repeatability both fit inside the depth of field window.

2. A focus adjustable build with a locking screw. Set at assembly and locked. This is the usual choice when the standoff is defined by a fixture that gets serviced, or when the module is assembled by hand.

3. Two fixed builds for two standoffs. Less costly than a mechanism when the machine does the same job at two distances and a re-focus between runs is acceptable.

Mechanical and Environmental Fit Before the Housing Is Drawn

Three figures decide whether a part bolts into the design: the barrel diameter sets the bore, the total track length sets the depth reserved between the front element and the sensor, and the mount thread decides which holder and focus detail carry over from the rest of the platform.

Barrel diameter is already on the table from the reading question above: φ14mm for the JSD1330, φ11mm for the JSD1660. On a small robot head or a gimbal, those three millimetres are usually the difference between one mechanical concept and another. Total track length is 21.87mm and 18.15mm respectively, and the published figure and the value on a particular build drawing can differ by a fraction of a millimetre; on a housing drawing that difference is real metal, so the drawing of the build being purchased is the reference. The M12 S thread is shared across the family, which means one holder platform can carry a second focal length when a project later needs a different field at a different standoff.

• Ingress protection. No ingress rating is published for the JSD1330 or the JSD1660, so an exposed outdoor or washdown position on a mobile robot needs a sealed housing around the optics, or a different sealed route. A machine that is washed down or rained on should have that stated in the enquiry rather than discovered after the sample arrives.

• Filter configuration. A 650nm and an 850nm filter option are available for this build, and each is a separate decision from the lens design. An infrared cut filter preserves colour under broadband light; an infrared corrected design keeps focus stable when the scene is lit in the near infrared. Fix the illuminator band and the ambient conditions first, then the filter follows.

❓ Frequently Asked Questions