1.1-inch Camera and Telecentric Lens Matching Guide

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What "1.1-inch" Really Means (and the Number That Actually Decides)

Imaging sensor formats are legacy video-tube labels, not physical dimensions. A "1.1-inch" sensor is not 27.94 mm wide. For the sensor family used in machine vision, a 1.1″ active area is approximately 14.19 × 10.30 mm. The physical dimension that governs whether a lens works is the diagonal, because the image circle is round and the sensor rectangle must fit inside it.

Using the Pythagorean relation, diagonal = √(w² + h²), the 1.1″ diagonal is ≈ 17.5 mm (calculated). For comparison, on the same calculation basis:

• 2/3″ (8.4 × 7.1 mm) → diagonal ≈ 11.0 mm (calculated)
• 1″ (13.13 × 8.76 mm) → diagonal ≈ 15.8 mm (calculated)
• 1.1″ (14.19 × 10.3 mm) → diagonal ≈ 17.5 mm (calculated)

So moving from 1″ to 1.1″ adds only ~1.7 mm of diagonal, but it crosses a practical threshold: many lenses are designed with a nominal image circle just large enough for 1″ and no more. This is why "it fits 1-inch, so 1.1-inch should be nearly the same" fails in the field. If you want the underlying geometry rather than the 1.1″ special case, see our general explainer on sensor size and image circle matching.

Rule One: Image Circle ≥ Sensor Diagonal (Never Equality)

The single hard constraint is:

Image circle diameter (Φ) ≥ sensor diagonal + margin

The margin is not decoration. It absorbs lens-to-lens build tolerance, sensor die placement tolerance inside the camera body, C-mount thread concentricity, and the fact that the usable illuminating circle is slightly smaller than the nominal circle at the extreme field edge. For the POMEAS 1.1″ bi-telecentric lens, the image circle is specified as Φ18.4 mm against a 1.1″ diagonal of ≈17.5 mm — a margin of about 0.9 mm (calculated). That margin is deliberately sized for a 1.1″ sensor and would not tolerate a 4/3″ sensor.

If the image circle is smaller than the diagonal, the failure is not subtle: the image corners go dark and, more importantly for metrology, the usable field becomes a rounded-rectangle that no longer matches the sensor's coordinate mapping. A lens that covers 2/3″ will cut a 1.1″ sensor down to an effective 2/3″ frame — you paid for 1.1″ pixels and use about 11 mm of them.

Which POMEAS Lenses Can Take a 1.1" Sensor — and Which Cannot

The table below lists maximum supported sensor format per model. This is the fastest way to avoid the classic mistake of pairing a 1.1″ camera with a 2/3″ lens.

Read the table as a two-step filter: format filter first, resolution filter second. Only the first two rows survive a 1.1″ sensor requirement. A 2/3″ lens such as PMS-LTCM1-110C may look attractive on resolution and price, but it physically cannot cover the sensor.

Mount and Back Focus: C-Mount, F-Mount and the Adapter Trap

Sensor format decides optics; the mount decides whether the mechanical stack is possible. Two interface families dominate: C-mount and F-mount. As industry-standard interface definitions (not a POMEAS product specification):

The trap is mechanical, not optical. A telecentric lens is designed for a fixed object-to-image distance; the 1.0X 1.1″ lens specifies an image/object distance of 260.41 ± 2 mm and a barrel length of 132.88 mm. Insert a C-to-F adapter, a filter holder, or a nominal "extension ring", and you change the image distance — magnification shifts, the telecentricity condition degrades, and the calibration you ran last week is no longer valid. Correct practice:

1. Choose the lens whose native mount matches the camera. Adapters are a last resort, not a standard build item.
2. If an adapter is unavoidable, re-run the magnification and FOV check after assembly (next section) — do not carry over the old numbers.
3. Verify the adapter's clear aperture is at least the image circle Φ. A narrow adapter bore behaves exactly like a small image circle: dark corners.
4. Confirm the adapter is not vignetting mechanically — a 1.1″ sensor needs a generously bored adapter, which many cheap generic rings are not.

Mount availability per model, and whether POMEAS stocks 1.1″-capable C-mount/F-mount adapters, must be confirmed with our product team (to be confirmed).

Magnification ↔ FOV: The Formula and a Worked Example

For a telecentric lens the relationship is linear and — unlike an entocentric lens — constant across the whole field:

FOV = sensor dimension ÷ β and β = sensor dimension ÷ FOV

where β is the lens magnification and the sensor dimension is the corresponding active width (or height) of the camera.

Worked example (PMS-10110CVP111T, β = 1.0X, 1.1″ sensor):

• Sensor active area: 14.19 × 10.30 mm
• FOV width = 14.19 ÷ 1.00 = 14.19 mm
• FOV height = 10.30 ÷ 1.00 = 10.30 mm
• Result: FOV = 14.19 × 10.30 mm

This matches the official POMEAS sensor-to-FOV table for the lens, which also lists 2/3″ (8.4 × 7.1 mm → FOV 8.4 × 7.1 mm) and 1″ (13.13 × 8.76 mm → FOV 13.13 × 8.76 mm) — identical sensor and FOV figures confirm β = 1.0X.

Second example — working backwards from a required FOV: you need to inspect a 20 mm-wide part on the same 1.1″ camera. Required β = 14.19 ÷ 20 = 0.71X (calculated). No 0.71X model exists in the 1.1″ line, so the nearest qualified option is the 0.37X lens: FOV = 14.19 ÷ 0.37 = 38.35 mm wide and 10.30 ÷ 0.37 = 27.84 mm high (calculated) — roughly 38.4 × 27.8 mm. That overshoots a 20 mm part, so a 1.0X lens on a 2/3″ camera may be the more economical answer (see the last section).

Corner Illumination and Vignetting: a 15-Minute Self-Check

Never accept "the lens fits the sensor" as proof. Run this check on the assembled camera + lens + light:

1. Uniform target. Place a matte white diffuse target (or an opal diffuser over a stable backlight) so it fills slightly more than the entire field.
2. Expose safely. Set exposure so the image centre sits at roughly 70–80% of full scale — clipping hides falloff.
3. Sample five regions. Read mean grey value in a small ROI (about 5% of image width) at the centre and at the four corners.
4. Compute the ratio. corner mean ÷ centre mean, per corner. A ratio near 1.0 means uniform. Falling corners mean something in the chain is limiting the circle.
5. Rotate to localise. Rotate the camera 90° about the optical axis. If the dark corners follow the sensor orientation, the limit is optical or mechanical (image circle too small, or an adapter bore blocking the light). If the dark corners stay fixed in space, the limit is the light (uneven illumination), not the lens.
6. Re-verify after any change in mount, adapter or WD.

A practical acceptance rule of thumb is to keep every corner within about 10% of the centre grey level (≈0.9 ratio) for measurement work, tightened or relaxed per project; this threshold is an engineering guideline proposed here, not a POMEAS product specification (to be confirmed with your acceptance criteria). For deeper background on why corners darken, our article on vignetting at the corners of low-magnification imaging covers the mechanism and the fixes.

When a 1.1" Camera Is Actually the Wrong (and Costlier) Choice

Bigger sensor is not automatically better. Four cases where a 1.1″ camera is the more expensive mistake:

If your application is dimensional measurement rather than defect detection, the accuracy argument for telecentric optics — constant magnification and low distortion across the field — usually outweighs raw pixel count. And when the goal is a cheap large field rather than measurement, telecentric optics may not be the right family at all; our note on when a telecentric lens is the wrong choice is the honest counterpoint.

Selection Steps

1. Get the true active area, not the label. Record width × height and pixel pitch from the camera datasheet. Do not use the "1.1 inch" string.
2. Compute the diagonal with √(w² + h²); add a working margin (about 0.5–1.0 mm is typical for a well-made pair).
3. Filter the catalogue by image circle. Require Φ ≥ diagonal + margin. Discard every 2/3″, 1/2″, 1/1.8″ model immediately.
4. Compute required magnification from the part: β = sensor dimension ÷ required FOV. Pick the closest catalogue magnification.
5. Check WD, depth of field and object resolution at that magnification against the measurement tolerance.
6. Resolve the mount and back focus before ordering: native C or F, no unexplained adapter rings, adapter clear aperture ≥ image circle.
7. Run the corner shading self-check on the assembled stack, then lock the calibration.

Talk to a Lens Engineer About Your 1.1" Sensor

Send us your camera's active area, your required field of view and your measurement tolerance, and we will tell you whether the 1.0X 1.1″ bi-telecentric lens, the 0.37X model, or a smaller-format combination is the better trade — including the corner behaviour you should expect. Start from our telecentric lens range or go straight to the contact page. If you are still choosing between families, the telecentric lens selection guide is the wider starting point.

Frequently Asked Questions

Can I use my 1.1-inch camera with a 2/3-inch telecentric lens?

Physically the mount will connect, and the image will look sharp in the centre — which is exactly why people do it by mistake. But a 2/3″ lens has an image circle sized for roughly an 11 mm diagonal, while a 1.1″ sensor needs about 17.5 mm. The result is heavy corner darkening and a genuinely usable field of only about the 2/3″ area. You are paying for a 1.1″ sensor and using a fraction of it, and the corner geometry no longer matches the sensor's pixel map, which breaks measurement calibration. The fix is to select a lens rated for 1.1″ — for example the 1.0X bi-telecentric model with a Φ18.4 mm image circle — rather than to accept the crop.

How do I know whether my lens image circle covers my sensor?

Two numbers decide it. First, compute the sensor diagonal from its active width and height using the Pythagorean relation. Second, compare it with the lens image circle diameter stated in the lens datasheet, and require a margin rather than an exact match. For a 1.1″ sensor with a 14.19 × 10.3 mm active area, the diagonal is about 17.5 mm, so a Φ18.4 mm image circle leaves roughly 0.9 mm of margin. If you cannot find an image circle figure for a lens, treat that as a missing specification, not as "probably fine", and ask the supplier to confirm before ordering.

Does a 1.1-inch sensor give me better measurement accuracy?

Not by itself. Measurement accuracy in a telecentric setup is driven mainly by magnification, lens distortion, telecentricity and depth of field — not by sensor area. Adding sensor area only helps if the lens can actually deliver resolution across that larger field and the light is uniform to the corners. It is common to find that the object-side resolution is limited by the lens: if a 0.37X lens resolves around 11.18 μm at the object, more pixels behind it record the same blur at higher data volume. Treat a larger sensor as a way to cover a larger field at the same magnification, and confirm resolution separately.

Why is the object-to-image distance so important on a telecentric lens?

A telecentric lens is a fixed-geometry instrument. The 1.0X 1.1″ bi-telecentric lens is specified with an image-to-object distance of 260.41 ± 2 mm and a barrel length of 132.88 mm. That geometry sets the magnification, keeps magnification constant with defocus, and preserves the low-distortion, near-parallel projection that makes the lens useful for measurement. Insert an adapter or extension ring that changes that distance and all three properties shift together. The image may still look acceptable, but the numbers you calibrated against are no longer valid, which is far more dangerous than an obviously soft image.

How much corner darkening is acceptable?

It depends on the job, but for measurement you want the corners to behave like the centre. A reasonable starting point is to keep the mean grey value at each corner within about 10% of the centre value when imaging a uniform white target. Anything worse deserves investigation before acceptance. Critically, always localise the cause: rotate the camera about the optical axis. If the dark corners rotate with the sensor, the limit is optical or mechanical — image circle too small, or an adapter bore narrowing the light path. If the corners stay in the same place in space, the problem is the illumination, not the lens.

Should I choose the 1.0X or the 0.37X 1.1-inch lens?

It is a field-of-view decision, not a quality ranking. The 1.0X lens maps a 1.1″ sensor to a 14.19 × 10.30 mm field with a working distance of 110 mm and a depth of field of 0.66–1.60 mm — the right choice when you need close-up detail and a shallow, precise measuring plane. The 0.37X lens gives roughly a 38.4 × 27.8 mm field at a 150 mm working distance with a deeper 3.6 mm depth of field, which suits larger parts or parts with height variation. Compute the required magnification from your part size first; the lens then follows. Send us both numbers and we will confirm the pairing.