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Basler C125-0418-5M machine vision lens
BaslerC-mount lenses
  • Rosepetal compatible
  • Recommended by AIS Vision

Basler Lens C125-0418-5M f4mm

C125-0418-5M

The Basler C125-0418-5M is a fixed focal length C-mount lens with a 4 mm (nominal 4.09 mm) focal length and maximum aperture of F1.8, optimized for 5 megapixel sensors with 2.2 µm pixel pitch. It covers a 1/2.5" image circle (7.3 mm diameter) and delivers a center resolving power of approximately 230 lp/mm. The lens features manual focus and manual iris with locking screws, a back focal length of 8.09 mm, and an overall optical length of 39.74 mm, weighing approximately 55 g. Designed in cooperation with Fujinon, it provides a wide 76.4° horizontal field of view on 1/2.5" sensors with visible wavelength coverage (400–700 nm).

Brand
Basler
Focal length
4 mm
Lens mount
C-mount
Aperture (f-number)
F1.8–F22
Image circle / max sensor
7.3 mm (1/2.5")
Optical resolution
5 MP
Telecentric
No
Working distance
100 mm – ∞
Weight
55 g
Operating temperature
-10 to 50 °C
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Technical overview

The Basler C125-0418-5M is a 4 mm (nominal 4.09 mm) fixed focal length C-mount lens co-developed with Fujinon specifically for 5 MP sensors with a 2.2 µm pixel pitch. Its 7.3 mm image circle covers the 1/2.5" format completely, making it a natural pairing for any 5 MP C-mount camera built on that sensor format. At F1.8 maximum aperture, the lens gathers sufficient light to run at short exposure times in moderately lit machine vision cells without requiring extreme strobe power — particularly valuable when imaging moving parts on a conveyor. The adjustable iris to F22 gives integrators control over depth of field and diffraction trade-offs, and both focus and iris positions lock with set screws to prevent drift after calibration, a critical feature in production environments subject to vibration.

At 4 mm focal length the lens delivers a 76.4° horizontal field of view on a 1/2.5" sensor, which translates to an exceptionally wide scene capture from close proximity. Combined with a minimum working distance of 100 mm, this makes the lens well-suited to compact stations where the camera must be mounted close to the subject — robot end-effectors, small inspection enclosures, or under-conveyor viewing positions. The center resolving power of approximately 230 lp/mm is matched to the 2.2 µm pixel pitch of a 5 MP sensor (Nyquist limit ~227 lp/mm), meaning the lens does not bottleneck sensor resolution. Visible wavelength coverage spans 400–700 nm, so the lens operates correctly with standard white, red, blue, or green LED illumination across that range without requiring corrective filters.

This is a conventional (non-telecentric) entocentric lens, so perspective projection means that object features closer to the camera appear proportionally larger — a normal trade-off at this focal length and working distance. For applications requiring sub-pixel dimensional measurement accuracy across depth variation, this must be accounted for in calibration. For presence/absence, surface inspection, barcode reading, or robot guidance where absolute metrology is secondary, the perspective effect is negligible. At 55 g and 39.74 mm optical length the lens is compact and light enough for robot-mounted or gantry-mounted camera assemblies where payload and envelope constraints apply. The operating temperature range of -10 to 50 °C covers typical indoor factory environments.

Best for

  • Wide-area close-range inspection in compact stations — the 76.4° FOV at a 100 mm working distance captures a large scene footprint when the camera cannot be mounted far from the part, such as inside a small enclosure or on a robot wrist.
  • 5 MP area-scan cameras on 1/2.5" C-mount sensors — the lens is optimized for the 2.2 µm pixel pitch of this format and fills the image circle without vignetting, preserving full sensor resolution.
  • Surface and packaging inspection under LED ring or bar lighting — the F1.8 aperture makes efficient use of visible-spectrum LED illumination at 400–700 nm, reducing strobe power requirements and enabling shorter exposure times.
  • Robot guidance and pick-and-place vision — the light weight (55 g), compact form factor, and locking focus/iris screws make this lens practical for camera-on-robot mounting where vibration could otherwise shift optical settings.
  • OCR/OCV and code reading on labels or parts — the center resolving power of 230 lp/mm matched to 5 MP resolution provides sufficient spatial detail to resolve small characters and 1D/2D code elements across a wide field.

Selection notes

  • Sensor format compatibility is strict: the 7.3 mm image circle covers 1/2.5" sensors but will vignette on larger formats such as 1/2" or 2/3". Confirm the target camera's sensor format before pairing.
  • This lens is optimized for sensors with 2.2 µm pixel pitch. Pairing it with cameras that have coarser pixels (e.g., 3.45 µm or larger) will underutilize the lens resolution; pairing with finer pixels risks the lens becoming the resolution bottleneck rather than the sensor.
  • The lens is non-telecentric, so magnification varies with working distance. Applications requiring accurate dimensional measurement across parts with height variation should apply field calibration or choose a telecentric lens instead.
  • Visible wavelength range (400–700 nm) means the lens is not corrected for near-infrared illumination. If the application uses NIR lighting (e.g., 850 nm for surface enhancement or back-lighting silicon), chromatic shift will cause focus error and resolution loss.
  • Both focus and iris must be set and locked manually — there is no motorized or auto-iris function. Ensure the integration process includes a focus verification step and that set screws are torqued consistently across units to maintain repeatability across camera replacements.

Specifications: General
BrandBasler

Specifications: Optical
Focal length4 mm
Lens mountC-mount
Aperture (f-number)F1.8–F22
Image circle / max sensor7.3 mm (1/2.5")
Optical resolution5 MP
TelecentricNo
Working distance100 mm – ∞

Specifications: Environment
Operating temperature-10 to 50 °C

Specifications: Mechanical
Weight55 g

Frequently asked questions

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