CS mount vs S-mount camera variant: choose at order time

You are ordering a compact vision camera and the data sheet lists two versions of the same body: a CS-mount variant and an S-mount variant. The sensor, the electronics and the driver are identical; only the nose of the camera differs. That one field of the order code decides which lens family the camera can accept for its whole service life, because the mount is machined into the front plate and the two variants are separate products. This guide gives you the decision rule, the flange numbers behind it, a worked focal-length example and the bench checks that close the order out.

What actually differs between the variants

CS-mount and C-mount share the same 1-inch-32 thread and differ only in flange focal distance: 17.526 mm for C, 12.526 mm for CS. The gap is exactly 5.000 mm (17.526 - 12.526). A C-mount lens on a CS-mount body needs a 5 mm spacer ring to reach focus. A CS-mount lens on a C-mount body sits 5 mm too far forward and focuses only on near objects, the failure mode walked through in lens focuses only at close distance. The ring options and clearances are covered in C mount vs CS mount.

S-mount shares nothing with that family. It is the M12 thread, about 12 mm across, and an M12 lens focuses by turning in the thread and locking, with no fixed register of its own. The screw physics behind that adjustment are in M12 lens thread pitch and focus shift. Mount vocabulary is collected in the machine vision glossary.

Everything else matches between the variants: sensor, resolution, frame rate, connector. Nobody converts one into the other in the field, so the choice belongs at order time.

The decision rule

Adapters only ever mount a smaller thread into a larger one. A CS-mount body takes CS lenses directly, C-mount lenses over the 5 mm ring, and M12 lenses over an M12-to-CS ring. An S-mount body takes M12 lenses and nothing else: a 1-inch-32 barrel will never enter a 12 mm thread. That asymmetry is the whole decision, and it commits as follows:

• At or under 6 mm focal length, on a 1/2-inch or smaller sensor: order the S-mount variant. The M12 range is dense there, in short, light barrels.
• Between 6 and 25 mm: both mounts are dense. Order by the lens stock you already hold and by the space around the camera.
• Longer focal lengths, any varifocal or motorized zoom, any iris control, or any sensor larger than 1/1.8-inch: order the CS variant. Telecentric work has its own decision path in entocentric vs telecentric lenses, and that glass, like the large-format ranges in machine vision lenses, is C-mount. The motorized zooms sit in CCTV lenses on C and CS mounts.

A varifocal lens, 6-15 mm for 2/3-inch sensors at up to 3 MP, in a C-mount barrel:

Barrels of that class thread straight into the CS variant. No S-mount body accepts them.

How to choose at order time, step by step

1. List the lenses you already own. Existing C or CS glass anywhere in the plant argues for the CS variant, which accepts all of it, directly or over a ring.
2. Size the focal length for the next station. Magnification is sensor width divided by field of view; run it in the lens focal length calculator or follow the worked example below. An answer under 6 mm puts the S-mount variant in play.
3. Confirm the mount carries that focal length for your sensor. In M12 board lenses the selection concentrates under 6 mm and thins beyond 25 mm; long glass, zooms and 1-inch formats live in the C and CS families. Format, focal length and IR-cut are worked through in M12 lens selection for board cameras.
4. Check image circle and resolution class. The image circle must cover the sensor diagonal, with the classes listed in the lens sensor format guide, and the megapixel class must meet the camera's resolution.
5. Check the mechanical envelope. The CS nose needs a clear opening just over 25 mm across; an M12 lens passes through about 12 mm. On a vibrating fixture the short M12 thread is the weak link: plan a lock ring, or take the CS variant with heavier glass.
6. Order the matching variant and read the mount line back. Variants are separate order codes. Confirm the mount field on the data sheet at checkout, not after the box arrives.

Worked example: 240 mm tray at 150 mm on a 1/2-inch sensor

A compact cell needs one overview camera watching a 240 mm wide tray. The frame fixes the working distance at 150 mm, and the camera family is offered in both variants around a 1/2-inch sensor with 6.4 mm of active width. Which variant goes on the order?

The rule in words: magnification is sensor width over field of view, and focal length is working distance times magnification over one plus magnification.

• Magnification: m = 6.4 mm / 240 mm = 0.0267.
• Focal length: f = 150 mm × 0.0267 / 1.0267 = 4.0 mm / 1.0267 = 3.9 mm.
• The nearest standard focal length is 4 mm. Solve the working distance back for it: WD = 4 mm × 1.0267 / 0.0267 = 154 mm, so the camera mounts at 154 mm.

The decision: 3.9 mm sits well under the 6 mm threshold on a 1/2-inch sensor, so the order is the S-mount variant and a 4 mm M12 lens. The CS variant would need a sub-6 mm C or CS lens in a larger barrel and gains nothing at this focal length.

Two M12 lenses that bracket the useful range, a 2.8 mm at 8 MP and a 25 mm at 5 MP:

The same 12 mm in each mount

Mid-range focal lengths exist in both mounts, and the data sheets show what really separates them: sensor coverage and barrel size. One focal length, one resolution class, two mounts:

All 2 share: Focal length 12 mm. Values as printed in each product's data sheet; open a part for its drawing and full specifications.

The LS-CTV-0012 serves a 1/2.5-inch sensor with an image circle up to 8 mm, in a fixed CS-mount barrel. The LS-MBL-0113 covers a 1/1.8-inch sensor with an 8-11 mm image circle. Choose the lens by sensor first and mount second; light gathering then follows the f-number in either family, a trade-off worked through in M12 lens light gathering.

Checks before you order

• Sensor diagonal against image circle. A 1/1.8-inch sensor has roughly an 8.9 mm diagonal and needs the 8-11 mm image-circle class; smaller sensors take the up-to-8 mm class.
• Resolution class against camera. A 5 MP lens in front of a 12 MP sensor wastes the sensor; match the classes at purchase.
• Front-hole clearance. Just over 25 mm for the CS nose, about 12 mm for an M12 lens. Measure the enclosure or bracket hole before ordering either variant.
• Vibration. Short M12 threads creep loose on shaking fixtures. Lock rings help; C-mount anti-vibration lenses exist when the fixture will not calm down.
• Illumination band. If the station lights with infrared, the lens must hold focus in that band, or the focus set under bench light drifts in production.
• Growth. A later zoom, iris, telecentric lens or larger sensor all point at the CS variant, the only one of the two that can host them.

When the usual answer is wrong

Order CS for flexibility fails at short focal lengths. Under 6 mm on a 1/2-inch or smaller sensor, the M12 range holds the choice in lighter, shorter barrels. Flexibility that is never used still costs diameter, weight and mounting space.

Adapt it later runs one way only. The M12-to-CS ring fits an M12 lens to a CS body; no ring fits a 1-inch-32 lens into an M12 nose. Board cameras with the larger M16 thread are a different body and can take C-mount glass through an adapter, as C-mount lens on an M16 board camera shows.

A CS lens on a C-mount body is not close enough. The 5.000 mm of missing flange eats the entire focusing range; the image stays sharp only at near distances.

Never choose the mount before the sensor. No M12 lens covers a 1-inch sensor, so a plausible sensor upgrade makes the CS variant the only path that survives it.

Verify it on the bench

1. Thread the lens in by hand until it seats. If it binds early, back out and restart: a cross-threaded aluminum nose is a write-off. The safe sequence is in camera lens mount thread binding.
2. Focus at the real working distance, then check all four corners before locking, as M12 lens focusing walks through. Corners reveal a lens a fraction of a turn off.
3. With a C-mount lens and the 5 mm ring on a CS body, recheck focus after tightening the ring; ring rotation can pull the lens off the mark.

For the next station, start in the lens finder or run the configurator from the lens step. If the decision still hangs on a lens you have not chosen, send the sensor and the field of view through the contact page; those two numbers settle the variant.