Kowa C-Mount FA Lens Alternatives: 6 Parameters to Verify Before Switching

C-mount FA installations look like the easiest optics to re-source: standard mount, standard focal lengths, twelve millimetres in every catalogue. What makes the swap hard is that the class spans two families usually compared against one part number — a wide-angle area lens built for a 1-inch sensor, and a line-scan lens built to cover an 80-odd-millimetre line through an M72 thread. They are not selected from the same numbers.

In the POMEAS global company-intelligence database, 10 of 2,602 surveyed companies have public material recording Kowa optics among their equipment. That figure indicates the deployment class, nothing more: no Kowa specification is quoted below, none having been independently verified.

Six parameters to verify before substituting a Kowa C-mount FA lens

Two of these apply differently depending on whether you are replacing an area-scan lens or a line-scan lens. The checklist order is the same; what the numbers mean is not.

1. Focal length and the coverage class you are actually replacing

Establish the class first. An area lens is chosen from focal length and working distance, with horizontal field estimated by the thin-lens approximation:

FOV ≈ sensor width × working distance / focal length

This estimate is not a measurement. it ignores lens extension and where focus actually sits. A line-scan lens is not chosen this way at all: it is matched to the length of the line sensor and the magnification the station needs, and its focal length is the consequence rather than the input.

Mixing the two classes is the common error: comparing the 146 mm line-scan focal length against a 12 mm area lens because both are "the focal length" produces nothing useful.

2. Image circle versus sensor format: where vignetting starts

Coverage is one comparison: the image circle has to reach every corner the sensor uses. On area lenses the check is expressed as a format, and the POMEAS pages also give the dimensions — 1-inch listed as 12.8 × 9.6 mm with an image circle of φ16 mm. A 2/3-inch crop inside that circle is supported and loses field, not light.

The widest member of a series also lives closest to the edge of its own coverage, so its corners deserve attention first.

3. Distortion, quoted per format and per field position

Distortion is not one number per lens. It changes with field position, so it is quoted against a field height written as y, and it changes with sensor size, because a smaller sensor crops out the worst of the field.

Published spread within this one family is wide and should be read literally: -3.73% @ y = 8.0 mm at 16 mm focal length, -2.06% @ y = 8.0 mm at 25 mm, and nothing at all for the 12 mm. Where a page publishes the 1-inch and 1/2-inch figures but not 2/3-inch, request the value rather than interpolating it.

4. Aperture range and the closest distance it will focus

Read the convention before the number. Several lenses in this class publish a focus range written as 1 m to ∞ rather than a minimum object distance: 1 m is the near limit and there is no working below it. Other families publish a minimum object distance instead, and treating the two as one unit costs the first candidate.

Aperture follows the same caution: three area lenses here share F1.6–F22 while differing entirely in field and distortion, so aperture alone distinguishes almost nothing.

5. Back focal length in air

Distance from the rear reference surface to the image plane, measured in air, and the value most often omitted because the new lens threaded on without complaint. Mechanical fit is not optical fit: if the flange geometry of the camera and the back focal length of the lens disagree, focus lands everywhere except where it is needed.

It is published per model and moves within a series — 13.54 mm, 12.17 mm and 12.69 mm across three focal lengths here. The line-scan models publish nothing, which puts this question at the top of any line-scan enquiry.

6. Mount, filter thread and operating temperature

C-mount handles the area lenses, but accessories do not follow: M37.5 × 0.5 on one model and M33.7 × 0.5 on another in the same family, nothing published for the third.

For line scan the mount changes class outright — M72, not C-mount. Temperature is published as -10 °C to +50 °C on the area lenses; one page additionally publishes humidity of 30%–80%, non-condensing, and no line-scan page publishes either.

Where POMEAS optics land on those six

Values published on the POMEAS product pages for three 1-inch C-mount area lenses and two M72 line-scan lenses:

Reading the table against the six checks:

- 12 mm. Widest coverage at 68.8° × 57.1° × 44.1°, and the only page publishing humidity (30%–80%, non-condensing). No distortion figure, so it cannot be specified into gauging work without asking. - 16 mm. Publishes the largest distortion here, -3.73% @ y = 8.0 mm — the honest cost of a 44.2° × 33.5° field on 1-inch. - 25 mm. The only area model publishing resolution too: 160 lp/mm centre, 100 lp/mm edge. Distortion covers 1-inch and 1/2-inch but not 2/3-inch, although 2/3-inch angles are given. - Line scan. LLC026 and LLC05 share headline optics exactly and differ only in published working distance sets.

Specifications published on different product pages were not necessarily measured under identical conditions and should not be read as a ranking.

What those numbers mean on the line

Scenario 1 — Wide station that has to cover a large part in one frame

Where one frame must hold the whole part, coverage dominates and the 12 mm at 68.8° diagonal is the candidate. Take it knowing what is unpublished: no distortion figure, and a 1 m near limit that rules out anything closer.

Scenario 2 — The output is a dimension, not an image

Distortion enters every dimensional result at the field position of the feature. Moving from 25 mm to 16 mm on the same 1-inch sensor moves published distortion from -2.06% @ y = 8.0 mm to -3.73% @ y = 8.0 mm. Neither figure is wrong; both belong in the uncertainty budget or must be calibrated out with the lens fitted.

Scenario 3 — Line-scan station losing its lens

Two POMEAS line-scan models carry identical headline optics and are separated by working distance alone: LLC026 publishes 752 / 644 / 571 mm and 968 / 865 / 799 mm, LLC05 publishes 417 / 383 / 357 mm and 659 / 632 / 613 mm. Choosing between them is a question about where the camera sits, not about image quality.

Scenario 4 — One specification serving two camera generations

The 25 mm publishes enough to serve two formats: 36.2° × 29.0° × 21.8° on 1-inch and 25.0° × 20.0° × 15.0° on 2/3-inch, with distortion given for 1-inch and 1/2-inch. The gap is 2/3-inch distortion, so if the older camera is 2/3-inch you can compute its field and cannot compute its distortion.

Writing a replacement specification when the original lens is discontinued

Once the original part is gone, the specification you write is all that separates you from guessing twice. Write it in checklist order, leaving unavailable values as not published rather than importing them from another model.

Begin with what the station fixes: sensor format and active area, line length where the camera scans, pixel pitch, and the working distance the mechanics allow. State which selection method applies, because everything downstream depends on it.

Then require each value with its measurement condition: image circle in millimetres alongside the format name; focal length; field angles or line coverage for every format in use; distortion per format; aperture; focus range or minimum object distance, whichever is published; back focal length in air; mount; filter thread; temperature and humidity.

Close by stating how acceptance will be judged. Dimensional stations are signed off against known parts, not against images that look sharp, so name the feature sizes and tolerances.

What this comparison does not tell you

This is a parameter reference, not a compatibility statement. No claim is made that any POMEAS lens is a drop-in replacement for another manufacturer's lens, and none should be inferred. Whether a substitute works depends on the mechanical envelope, the flange geometry of the camera, whatever sits between mount and sensor, and the illumination.

The Kowa name appears only where documented in customer-supplied intelligence: evidence of what the market has installed, not a source of third-party specifications, and no Kowa figure is reproduced here.

Optical performance is not measurement accuracy. Distortion and field angles describe the lens; what the station reports also depends on pixel sampling, contrast, illumination stability, encoder synchronisation on line-scan stations, and the algorithm.

This page covers C-mount area lenses and M72 line-scan lenses. It does not cover telecentric optics, nor zoom-lens behaviour across a zoom range.

FAQ

Is a C-mount area lens and a C-mount line-scan lens the same selection problem?

No. Area lenses are chosen from focal length and working distance; line-scan lenses are matched to line length and magnification. The POMEAS line-scan models use M72 rather than C-mount.

What does a focus range of 1 m to infinity mean for my station?

It sets 1 m as the near limit. Several POMEAS 1-inch lenses publish the range that way instead of a minimum object distance, and a station imaging closer than 1 m needs a different family or a documented exception.

Can I use the 1-inch lens on a 2/3-inch camera?

Yes for coverage: the φ16 mm image circle exceeds the 2/3-inch sensor, and both field angles are published. What may be missing is the distortion figure for that smaller format, which has to be requested.

Why do two line-scan lenses share every headline specification?

PMS-LLC026 and PMS-LLC05 publish identical headline optics — 146 mm, 82 mm circle, M72 mount, F4.0–F16, distortion below 0.002% — so the published working distance sets are what separate them.

Why is distortion so much worse at 16 mm than at 25 mm?

Wide fields cost geometric accuracy. Published distortion at y = 8.0 mm on a 1-inch sensor is -3.73% at 16 mm and -2.06% at 25 mm; both are usable, but only if the number enters the uncertainty budget or is calibrated out.

Which of these publishes anything about humidity?

Only PMS-LFGH-1216M, at 30%–80% non-condensing. The other area pages publish a temperature range of -10 °C to +50 °C, and the line-scan pages publish no environmental values.

Talk to the engineering team

If you are specifying a replacement and need measured values for your own conditions — your sensor size, your working distance, your feature size — send us those four numbers and we will run them against the current catalogue and tell you what actually fits, including when nothing does.

https://www.pomeas-vision.com/Contact.html

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