Board camera lens mount thread sizes: M12 or M6

You have a small board camera on the bench, the lens is missing or due for replacement, and the seller has not answered the one question that decides the order: is the mount M12 or M6? You can settle it yourself in about two minutes with calipers, and the sensor format printed on the module usually tells you the answer before you measure. Below are the thread sizes you will actually meet on board cameras, how to read a barrel with no datasheet, the image circle a 1/4-inch sensor needs, and a worked field-of-view example — enough to order a replacement that threads in on the first try.

What lens mount does a 1 MP board camera use?

Almost certainly M12 x 0.5: the 12 mm S-mount thread is the default on board cameras carrying sensors from 1/4 inch up to 1/2 inch, and 177 of the 195 lenses in the M12 board lenses range use it.

The camera side agrees. Of the 120 board-level cameras in the range, 48 take an M12 lens, 47 a C-mount, 11 ship as bare boards and 4 are CS-mount. A 1 MP module with a 1/4-inch sensor — the class typically sold for embedded vision compute boards — sits in the middle of that territory: the barrel that screws into its holder is an M12 thread cut at 0.5 mm pitch.

M12 names the thread's major diameter; the x 0.5 names the pitch, the crest-to-crest distance. S-mount is the system name for the same mount, and CS mount vs S-mount camera variant: choose at order time covers that choice when you specify the camera itself. If a sales reply is slow, do not wait on it — the next section is the whole method.

How do I measure the lens thread without a datasheet?

Measure the thread's major diameter with calipers, then count crests: a barrel measuring 12 mm across the threads is M12, and the crest count over a 10 mm span confirms the pitch that nearly every board lens uses.

1. Unscrew the shipped lens and measure across the outside of the thread, crest to crest, at the undamaged end. A rolled or coated thread reads slightly small — expect 11.8-12.0 mm before you call it M12; a reading near 6 mm is the M6 mount.
2. Count crests across exactly 10 mm of barrel: 20 crests is a 0.5 mm pitch, and a count near 28 is the finer 0.35 mm pitch some barrels carry. Buy the pitch the holder is cut for, because the two do not interchange.
3. Lens lost? Measure the holder instead: a female M12 thread reads just under the nominal major diameter across the roots, and any M12 lens should spin in freely for at least one full turn before it begins to focus.

One full turn advances the lens by exactly one pitch, which is also why S-mount focus is so sensitive to small rotations. How much image shift each turn buys is derived in M12 lens thread pitch and focus shift: the physics of S-mount focus.

Is M6 ever the right answer for a board camera?

Yes, but rarely: 3 of the 195 lenses in the range carry an M6 mount against 177 in M12, so a 6 mm barrel is real — measure it, because M6 turns up on the smallest pen-type modules.

M6 survives where even the standard M12 barrel is too wide: pen cameras, endoscope heads and the slimmest sensor boards. The same lens range carries one model each in M8, M9x0.5 and M10, plus 2 in M16 — C-mount lens on an M16 board camera: adapters and flange distance covers that larger thread. Measure first, then filter the lens finder by the mount you measured, not the one you assumed.

The decision is short. A measured 6 mm barrel means an M6 lens, and nothing else threads in. If the M6 range cannot reach the distortion or resolution the job needs, do not adapt the thread — move to a bare-board camera with an M12 holder and pick from the full 177-lens choice.

Does an M12 lens cover a 1/4 inch sensor?

Yes, twice over: a 1/4-inch type sensor measures about 3.2 x 2.4 mm, a 4.0 mm diagonal, and the smallest common M12 image-circle class covers up to 8 mm — twice that diagonal.

The rule is one line: the image circle must equal or exceed the sensor diagonal. In the M12 range, 128 lenses sit in the up-to-8 mm circle class and 67 in the 8-11 mm class built for 1/1.8-inch sensors. A larger-format lens on a smaller sensor always works — you simply use less of its circle — while the reverse vignettes the corners black.

The pairing ships as standard on the camera side too: LS-BCM-0059 is a GigE board camera with a split 1/4-inch sensor, a 1.0 MP mono image and an M12 lens mount.

What field of view will a wide M12 lens give?

About 225 x 168 mm at a 200 mm working distance, for a 2.85 mm focal length on the 3.2 x 2.4 mm sensor — a 70-degree diagonal, wide enough to frame a whole small assembly in one image.

The pinhole estimate, with the arithmetic shown:

At 200 mm the magnification is 3.2 mm / 225 mm = 0.014, so the pinhole form holds to within a few percent at these distances. Halve the working distance and the field halves with it: about 112 x 84 mm at 100 mm.

A 2.85 mm focal length in the standard M12 thread is an off-the-shelf part: LS-MBL-0090 is a 2.85 mm M12 board lens rated up to 3 MP for 1/2.9-inch sensors, with an image circle up to 8 mm.

Any other sensor, focal length or distance runs through the same arithmetic in the calculator below.

Which lens resolution rating does a 1 MP sensor need?

Order one class up: a 1280 x 960 array on the 1/4-inch format has 2.5 μm pixels and about 1.2 MP, so an up-to-3 MP rated M12 lens is the correct match for a 1 MP module.

The pixel arithmetic: 3.2 mm / 1280 pixels = 2.5 μm, and 2.4 mm / 960 pixels = 2.5 μm, for 1280 x 960 = 1,228,800 photosites. The Nyquist limit that sets is 1 / (2 x 0.0025 mm) = 200 lp/mm, the spatial frequency the lens must transmit for the sensor to see everything it can. Megapixel ratings are a shorthand for exactly that; when a job needs the last of the resolution, work in lp/mm instead, as sensor resolution in lp/mm: match lens MTF to pixel pitch shows.

Three wide M12 lenses from three resolution classes, all in the same thread, are compared below.

Values as printed in each product's data sheet; open a part for its drawing and full specifications.

For the 1 MP module the 2 MP class is enough. The 8 MP and 16-25 MP classes are the buy-once choice if a sharper sensor is coming — the thread does not change, so the lens carries over to the next board.

What if the camera is a bare board with no mount?

Then you choose the thread yourself: 11 of the 120 board-level cameras in the range ship as bare boards, and an M12 holder plus any of the 177 M12 lenses is the default build for small sensors.

The holder carries the female thread, screwed or soldered to the board, and lens accessories add focusing rings, adapters and holders around it. M12 has no fixed flange distance the way C and CS do: focus is set by how far the lens is threaded in, so the holder height is part of the optical design — lens focal length vs back focus in board cameras untangles that. Short threads can also run out of travel before the lens reaches close focus; M12 lens thread travel: why short threads lock out close focus gives the numbers.

After threading in, focus and lock: M12 lens focusing: adjust, check corners and lock. To assemble the whole optical chain in one pass, start at the lens step of the configurator or browse the lens finder.

When is M12 the wrong choice?

Above 1/2 inch: M12 lenses in the range stop at the 1/1.8-inch format and an 8-11 mm image circle, so 2/3-inch sensors, telecentric optics and long-working-distance macro belong on C or CS mounts.

The evidence: 40 lenses in the M12 range serve 1/1.8-inch sensors and none goes larger, while 47 of the board-level cameras are C-mount — including LS-BCM-0056, a 12 MP GigE board camera with a 1/2-inch sensor, a C-mount and 1.6 μm x 1.6 μm pixels. Even small sensors sometimes leave M12 for optics the thread cannot host: LS-MBL-0176 is a 4-20 mm CS-mount pinhole varifocal with a 12.53 mm back focal length for 1/2.7-inch sensors. The reverse case also holds: M12 reaches ultra-wide without trouble — LS-MBL-0041 is a 1.45 mm M12 fisheye for 1/2.3-inch sensors at 10 MP — so sensor size, not angle of view, is what pushes you off the thread.

More mount and optics questions are collected on the lenses topic page.

What should I check before ordering the replacement?

Five checks fix the order: measure the barrel, confirm the pitch, compare the image circle with the sensor diagonal, match the resolution class, and decide where the IR-cut filter lives.

• Barrel diameter, measured as in the steps above, names the mount: M12 or M6. Anything else, filter the finder by the mount you measured.
• Pitch: 20 crests per 10 mm is the standard pitch, a count near 28 is 0.35 mm. Order the pitch the holder is cut for.
• Image circle at or above the sensor diagonal: 4.0 mm for a 1/4-inch sensor, so the up-to-8 mm class clears it.
• Resolution class at or above the sensor's pixel count: up-to-3 MP for a 1.2 MP sensor.
• IR-cut location, because it changes colour balance and near-IR behaviour: M12 lens IR cut filter: is it in the glass or on the board and the M12 lens selection guide settle it.

Measured and checked, send the barrel diameter, the pitch and the sensor format through the contact page, and the part number follows from there.