The Blackmagic Design Spares - Camera URSA Broadcast - B4 Mount is a precision-engineered replacement lens mount designed specifically for the URSA Broadcast and URSA Broadcast G2. Because B4 lenses are the standard for electronic news gathering (ENG) and studio production, this mount is a critical interface that bridges high-end broadcast optics with the URSA’s digital sensor.
Optical and Mechanical Precision
The B4 mount is significantly more complex than a standard passive mount (like an EF or F mount). It features integrated optics designed to correct for the spherical aberration introduced by the three-color prism found in traditional B4 cameras.
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Spherical Aberration Correction: Since B4 lenses were originally designed for 3-sensor prism cameras, using them on a single-sensor camera like the URSA requires corrective glass. This mount includes high-quality optics that ensure the image is sharp across the entire sensor.
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Rugged Locking Mechanism: Features the classic "breech-lock" ring, allowing operators to secure heavy ENG zoom lenses with a rock-solid connection that prevents "lens sag."
Electronic Integration
The B4 mount spare is not just a piece of metal; it is an electronic bridge.
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12-pin Hirose Connection: The mount assembly works in tandem with the 12-pin broadcast connector on the side of the URSA chassis. This allows the camera to power the lens and provides the operator with control over iris, zoom, and start/stop recording via the lens handgrip.
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Lens Data Metadata: It facilitates the transfer of lens metadata (f-stop, focal length) directly into the Blackmagic RAW or ProRes files for post-production and VFX use.
Why You Might Need a Replacement
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Optical Scratches: Since this mount contains internal corrective glass, any scratches or fungus on that rear element will directly impact image quality.
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Mechanical Wear: The breech-lock ring can become loose or "gritty" over years of use in the field, leading to a lens connection that isn't perfectly light-tight.
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Electronic Pin Damage: While the 12-pin connector is on the camera body, the communication logic for the lens is tied to how the mount is seated. If the mount is warped due to a drop, the electronic connection may become intermittent.
Key Features
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Genuine OEM Spare: Guaranteed to maintain the correct flange focal distance (back focus) for B4 optics.
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Shim Kit Included: Usually ships with a set of precision shims to allow for fine-tuning of the back focus, ensuring the lens stays in focus throughout the entire zoom range.
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Durable Construction: Made from high-strength stainless steel and aircraft-grade aluminum.
Technical Installation Note
Replacing a B4 mount is a "clean-room" task that requires precise calibration:
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Sensor Protection: When the mount is removed, the camera's sensor is completely exposed. Perform the swap in a dust-free environment and keep the sensor protected with a body cap whenever possible.
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The Shimming Process: After installing the new mount, you must check the "back focus." If the lens is sharp at the wide end but soft at the telephoto end (or vice versa), you will need to add or remove the included shims behind the mount.
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Screw Torque: Use a high-quality Torx or Hex driver (as specified by the current revision) and tighten the mounting screws in a "star pattern." This ensures the mount is perfectly flush against the camera body.
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Avoid Fingerprints: Do not touch the rear corrective glass element. If you do, clean it only with professional lens cleaning solution and a high-quality microfiber cloth.
Are you seeing softness in your image that suggests the internal glass is damaged, or are you looking to convert an URSA Mini (EF/PL) into a Broadcast-ready rig?
