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

Compact, high-pixel-count C-mount installations usually get replaced in a hurry, because they sit where things fail: robot-mounted heads, hot cells, cold stores, and gantries where every gram matters. Those are also the places where the datasheet matters most, and where two habits cause trouble — assuming a small lens has small requirements, and reading one back focal length when the page publishes two.

In the POMEAS global company-intelligence database, 4 of 2,602 surveyed companies have public material recording Fujinon lenses among their equipment. That figure indicates the deployment class: no Fujinon specification is quoted below, none having been independently verified.

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

Where a page publishes nothing for one of these, the absence is the finding. Much of what follows concerns values that are not published, because those are the ones filled in from memory.

1. Focal length and the coverage class you are replacing

Focal length sets how much of the frame the part fills. Horizontal field is estimated by the thin-lens approximation:

FOV ≈ sensor width × working distance / focal length

An estimate, not a measurement, needing your own sensor width as input. Some series remove the need: the LFHHG pages publish object area directly, 121.0 × 96.7 mm on 4/3-inch for the 35 mm model at closest focus, with two smaller triples alongside.

Establish the class before comparing numbers. Maximum sensors here run from 2/3-inch image circle Φ11 mm through 1.1-inch at 17.6 mm to 4/3-inch at 23 mm, and a specification copied across those boundaries describes a different lens.

2. Image circle versus sensor diagonal: where vignetting starts

Coverage is one comparison: image circle ≥ every corner the sensor uses. The three formats above are stated differently — a circle diameter on one page, a format dimension on another — so normalise them before comparing, remembering that going down a format is safe while going up darkens corners.

Cross-class substitutions fail quietly. Pairing a high-pixel camera with a lower-resolution class produces a full-resolution image of a lower-resolution optic: pixels present, detail absent.

3. Distortion, quoted per format and per field position

Distortion is not one number per lens. It changes with field position, 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.

Two conventions appear in the table below. The 35 mm publishes conditioned figures: -0.52% @ y = 11.5 mm on 4/3-inch, -0.42% @ y = 8.0 mm on 1-inch, -0.12% @ y = 4.0 mm on 1/2-inch. The 25 mm publishes 0.50% with no field position. Both are usable; only one says where in the frame it was measured.

4. Aperture range and closest focusing distance

Aperture here is narrow and consistent: F2.8–F16 across the 20 MP series and the 50 mm 2/3-inch model, F2.0–F22 on the 4/3-inch model. It describes light and depth of field and little else.

Focus range discriminates more, and it is published every time: 0.1 m to ∞ on the 12 mm and 25 mm, 0.25 m to ∞ on the 50 mm of that series, 0.2 m to ∞ on the 35 mm, 0.3 m to ∞ on the 50 mm 2/3-inch model. Each is a floor, and the difference between 0.1 m and 0.3 m decides whether a compact lens suits a close station at all.

5. Back focal length in air, and the second figure beside it

Distance from the rear reference surface to the image plane, measured in air, deciding whether focus is reachable even when the thread fits. These pages are informative here and easy to misread: the 20 MP series publishes an optical figure and a mechanical figure side by side.

The 12 mm gives 14.45 mm against 10.63 mm, the 25 mm 12.7 mm against 11.3 mm, the 50 mm 10.3 mm against 10.08 mm, optical first. Which one your camera quotes determines which you compare. The 4/3-inch model publishes a single 18 mm in air; the 2/3-inch model publishes none.

6. Mount, mechanical detail and operating temperature

Every model here is C-mount, the 20 MP series stated as 1-32UN-2A. Mechanical values are what separate them for integration: the 25 mm publishes a C-mount protrusion of 6.2 mm, and weights run 130 ± 5 g, 126 ± 5 g and 118 ± 5 g across the series.

Temperature is where the class earns its place: -30 °C to +70 °C across the 20 MP models, -20 °C to +60 °C on the 4/3-inch model, nothing on the 2/3-inch one. No page here publishes a filter thread, so accessory fit has to be asked for.

Where POMEAS optics land on those six

Values published on the POMEAS product pages for five C-mount FA lenses across three sensor classes:

Reading the table against the six checks:

- 12 mm. Widest of the high-pixel group, reaching 0.1 m, with a published object area of 230 × 184 × 137 mm at closest focus. No distortion figure, so gauging work needs a request first. - 25 mm. The only one publishing a C-mount protrusion, 6.2 mm, and the only one with an unconditioned distortion figure. - 50 mm (20 MP). The tightest optical-mechanical back focal length pair, 10.3 mm against 10.08 mm, with distortion of 0.05% @ y = 16 mm. - 4/3-inch and 2/3-inch pair. One covers three formats with three conditioned figures and a single 18 mm back focal length; the other covers one format and publishes no mechanical values.

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 — Head mounted on a moving gantry in a hard environment

Every gram and every degree counts. The 20 MP series publishes -30 °C to +70 °C and weights of 118 ± 5 g to 130 ± 5 g: the class to look at where a robot carries the camera into a cycling cell. The trade is F2.8–F16, narrower than the 4/3-inch model's F2.0–F22.

Scenario 2 — Small features on a high-pixel-count camera

Resolution classes have to match: pairing the high-pixel camera with the 10 MP class 2/3-inch model wastes the sensor, since Φ11 mm serves neither format nor pixel count. Within the 20 MP group distortion runs from unpublished to 0.05% @ y = 16 mm at 50 mm.

Scenario 3 — Verifying coverage without doing arithmetic

Field-of-view formulas are estimates. The LFHHG pages publish object area directly: at closest focus, 0.2 m, the 35 mm covers 121.0 × 96.7 mm on 4/3-inch, with smaller triples alongside. Comparing that rectangle against the part beats deriving it from angles.

Scenario 4 — The datasheet quotes one back focal length, the page publishes two

This is the one that stops installations. The 12 mm carries 14.45 mm in air and 10.63 mm mechanical on the same datasheet. Before ordering, establish which convention your camera documentation uses, then compare against the matching figure; using the wrong one leads to a lens that threads on, focuses nowhere useful, and gets blamed on the mechanics.

Writing a replacement specification when the original lens is discontinued

Once the original is gone, the specification you write is what separates you from guessing twice. Leave unavailable values as not published rather than importing them from another model.

Start with the station: sensor format and active area, pixel pitch, the working distance the mechanics allow, and the environmental range the cell sees — one line that often removes half the candidates here.

Then require each value with its condition: image circle beside the format name; focal length; field angles or object area at closest focus; distortion per format with field position; aperture; focus range; back focal length, stating optical in air or mechanical; mount and protrusion; weight; temperature; filter thread.

Close by saying how acceptance will be judged. Dimensional stations are signed off against known parts rather than sharp images, 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 Fujinon 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 Fujinon figure is reproduced here.

Optical performance is not measurement accuracy. Resolution class and distortion describe the lens; what the station reports also depends on pixel sampling, contrast, illumination stability, camera calibration, and the algorithm.

This page covers fixed-focal-length C-mount FA lenses across three sensor classes. It does not cover line-scan optics, matched to line length through different numbers, nor zoom behaviour across a range.

FAQ

Why does one page publish two back focal length figures?

Because the optical distance in air and the mechanical distance from the reference surfaces differ. The 12 mm publishes 14.45 mm optical and 10.63 mm mechanical, so establish which convention your camera uses before comparing either.

What does 0.50% distortion mean without a field position?

It means the condition was not stated. The 25 mm publishes 0.50% alone, while the 35 mm publishes -0.52% @ y = 11.5 mm; only one of those tells you where in the frame it was measured.

Is the 20 MP series usable where the cell runs hot?

It publishes -30 °C to +70 °C, against -20 °C to +60 °C on the 4/3-inch model and nothing on the 2/3-inch model. Those are the widest published ranges in this group.

Can I check coverage without calculating field of view?

Yes, where the page publishes object area. The LFHHG 35 mm covers 121.0 × 96.7 mm at closest focus on 4/3-inch; comparing that rectangle to the part avoids estimates altogether.

Which focus ranges are available here?

0.1 m to ∞ on the 12 mm and 25 mm of the 20 MP series, 0.25 m to ∞ on its 50 mm, 0.2 m to ∞ on the 35 mm 4/3-inch model and 0.3 m to ∞ on the 50 mm 2/3-inch model.

Do these publish a filter thread?

None of the five does. Accessory compatibility has to be requested, and existing hoods or filters should not be assumed to fit any model in this group.

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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