Omron Vision Camera Lens Alternatives: 6 Parameters to Verify Before Switching

Substituting the lens on a running station is rarely blocked by availability. It is blocked by information nobody wrote down: the service record names the camera head, the purchase record names the part number, and the optical quantities that decide whether a replacement forms a usable image appear in neither place.

In the POMEAS global company-intelligence database, 12 of 2,602 surveyed companies have public material recording Omron vision systems among their equipment. That figure is evidence of how widely the deployment class is used, nothing more. No Omron specification is quoted below, none having been independently verified, and nothing here is a compatibility claim.

Six parameters to verify before substituting the lens on an Omron vision station

Focal length is the number everyone already has, and the least discriminating of the six. Below it sit five quantities that decide whether the image covers the sensor and whether focus is reachable.

1. Focal length and the sensor format the lens actually covers

Focal length sets the field of view, so it sets how much of the frame the part fills. For planning, horizontal field is estimated with the thin-lens approximation:

FOV ≈ sensor width × working distance / focal length

This is an engineering estimate, not a measured value. Using the sensor dimensions published on the POMEAS pages, where 2/3-inch is listed as 8.8 × 6.6 mm, a 400 mm working distance gives roughly 293 mm of horizontal field with an 8 mm lens, 141 mm with 25 mm and 101 mm with 35 mm.

The failure mode is not arithmetic, it is coverage. Every lens compared below is specified for a maximum sensor of 2/3 inch; on a larger sensor the corners fall outside the image circle whether or not the thread turns.

2. Image circle versus sensor diagonal: where vignetting starts

Coverage is one comparison: lens format ≥ camera sensor format. Larger merely wastes image circle; smaller darkens the corners first and quietly invalidates anything measured there.

A smaller sensor than the maximum is supported, and the pages often give both sets of angles so nothing has to be converted. The 8 mm lists 51.4° × 42.0° × 32.0° on 1/2-inch against 66.8° × 55.8° × 43.3° on 2/3-inch: the same part at the same distance occupies far more of the smaller frame.

3. Distortion, quoted per sensor format and per field position

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

Where a page publishes two figures side by side, they belong to two formats rather than two lenses: -0.53% @ y = 5.5 mm is the 2/3-inch value and -0.35% @ y = 4.0 mm the 1/2-inch value on the same family. They are not interchangeable. Of the four models compared below, one publishes distortion at all, and only for 2/3-inch. Where the value you need is absent, request it rather than borrow it from another model.

4. Aperture range and minimum object distance

The aperture range tells you how much light the lens passes and how much depth of field is available stopped down. The wide end differs across a family even where barrels look alike: F1.6 on the 8 mm, F1.4 on the 35 mm, F1.8 on the 50 mm, F2.0 on the 75 mm, all down to F22.

Minimum object distance is the harder constraint, because it is a floor rather than a recommendation. The 8 mm reaches 0.1 m, the 35 mm starts at 0.3 m, the 50 mm at 0.4 m and the 75 mm at 0.9 m. A fixture imaging at 250 mm cannot use the 35 mm or anything longer.

5. Back focal length in air

This is the distance from the rear reference surface of the lens to the image plane, measured in air, and it is the value skipped most often because the new lens threaded on without resistance. 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 you need it, and the symptom is usually misdiagnosed as a broken focus mechanism.

The number is per model, not per series: the 35 mm below publishes 12.82 mm while three siblings publish nothing. A filter, spacer or shim between the references shifts it too.

6. Mount, filter thread and operating temperature

Every model here is specified C-mount, which settles the interface but not the accessories. Filter thread is not uniform: the 35 mm publishes M37.5 × 0.5, and a hood bought for that thread will not necessarily fit its siblings. Operating temperature is published for the 35 mm and 50 mm at -10 °C to +50 °C, and not published for the 8 mm or 75 mm.

Weight belongs here too, as an envelope question rather than an optical one: 156 g for the 35 mm, 223 g for the 75 mm.

Where POMEAS FA optics land on those six

Values published on the POMEAS product pages for four 2/3-inch, 5.0 MP C-mount FA lenses:

Reading the table against the six checks:

- 8 mm. The wide option and the only one reaching 0.1 m. It also publishes the least: no distortion, no back focal length, no filter thread, no temperature. - 35 mm. The only member carrying published distortion, back focal length and filter thread together — what lets an optical term enter a measurement uncertainty budget at all. - 50 mm. Keeps the -10 °C to +50 °C rating but publishes neither distortion nor back focal length. - 75 mm. A standoff lens: 8.4° × 6.7° × 5.0° on 2/3-inch and 6.1° × 4.9° × 3.7° on 1/2-inch, for small targets seen from well back.

Values published on different 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 — Close-range station with a short fixed standoff

The station images at about 150 mm because that is all the fixture and lighting leave. The 35 mm cannot focus there, its floor being 0.3 m; neither can the 50 mm or 75 mm. Only the 8 mm reaches that distance, where the thin-lens estimate puts the horizontal field near 8.8 × 150 / 8 ≈ 165 mm.

Scenario 2 — Small target seen from clear of the product flow

Where the camera must stand back from a conveyor, distance is the requirement and field of view follows. The 75 mm gives 8.4° × 6.7° × 5.0° on 2/3-inch, and its 0.9 m floor means it can never be brought closer.

Scenario 3 — Several part numbers on one station

Multiple part sizes tempt you towards a zoom, and POMEAS does list a manual zoom variant on this 2/3-inch format spanning 12–36 mm. Take it knowing what the six checks become: field of view, distortion and focus position vary with the setting, so returning to a chosen magnification becomes a source of uncertainty.

Scenario 4 — Re-qualifying after the distortion changed

The likely outcome of a substitution is that everything fits, the image looks right, and the numbers quietly move. Across this group the published distortion status runs from not published to -0.07% @ y = 5.5 mm, with no way to reason from one to the other: recalibrate with the new lens fitted and check against known parts.

Writing a replacement specification when the original lens is discontinued

Once the original part is off the market, the specification you write is all that stands between you and a second round of guessing. Write it in checklist order, marking anything unavailable as not published rather than filling it in from a neighbouring model.

Start with what the station fixes rather than what the lens offers: the sensor format and active area installed, the pixel pitch it resolves, and the working distance range the mechanics allow.

Then list what the lens must publish, each with its measurement condition: focal length; maximum sensor format with the image circle in millimetres; field angles for the format you run; distortion at your field position, per format; aperture range; minimum object distance; back focal length in air; mount; filter thread; weight; operating temperature.

Finally, say how the result will be judged. A gauging station is accepted against measured parts, not against sharp-looking images, so include the feature sizes and tolerances that must be recovered.

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 a lens fitted to any camera head, and none should be inferred. Whether a substitute works depends on the mechanical envelope, the flange geometry of the camera, anything between mount and sensor, and the illumination.

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

Optical performance is not measurement accuracy. The figures quoted describe the lens; what the station reports also depends on pixel sampling, contrast, illumination stability, calibration artefacts and the algorithm.

This page covers C-mount fixed-focal-length FA lenses for area-scan cameras. It does not cover telecentric optics, the appropriate class when the output is a dimension across a part with height variation, or line-scan optics, which are specified against line sensors.

FAQ

Can I keep the same field of view by matching the focal length?

Only if the sensor is unchanged. Horizontal field is estimated as sensor width × working distance / focal length, so one focal length on a different sensor gives a different field.

What is back focal length in air, and why is it missing from my datasheet?

It is the distance from the lens rear reference surface to the image plane, measured in air, and it decides whether focus is reachable at all. POMEAS publishes it per model; several pages publish nothing, so it must be requested.

Will my existing filters and hoods fit the replacement?

Filter thread varies within a family: the 35 mm PMS-LFEH-3514(A) publishes M37.5 × 0.5 while other members publish no thread at all, so transfer should never be assumed.

Why does the widest lens in the series publish the fewest specifications?

Each datasheet is written independently. The 8 mm PMS-LFEH-0816M(A) publishes no distortion, no back focal length and no operating temperature, which is a reason to request those values rather than copy them.

The current lens focuses at 150 mm. Which candidates survive?

Only those whose minimum object distance falls below your working distance: here the 8 mm at 0.1 m, while the 35 mm starts at 0.3 m, the 50 mm at 0.4 m and the 75 mm at 0.9 m.

After swapping lenses the image is fine but the measurements moved. Why?

Distortion or magnification changed. Distortion enters every dimensional result at the field position of the feature, so recalibrate with the new lens fitted and re-verify against known parts.

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

Next Step

Send POMEAS your sensor format, working distance, field of view