Nikon Loses Key Patent Battle Against Viltrox in China

China’s patent office has ruled Nikon’s Z-mount accessory patent entirely invalid. This has struck a significant blow to the company’s infringement case against the China-based lens maker. The decision comes from the China National Intellectual Property Administration (CNIPA), which found the patent’s design lacked an inventive step.

The patent in question was granted back in 2021 and titled simply “Accessories.” It covered the core mechanical geometry of a lens mount: the arrangement of four bayonet lugs, the angles between them, and the placement of electrical contacts. Nikon argued the design prevented incorrect mounting, protected the contacts, and improved impact resistance. What is worth noting is that this patent doesn’t cover the entire Z-mount system, just this one piece of it.

How We Got Here

Viltrox filed the invalidation request back in December 2025, arguing the design was nothing a skilled engineer couldn’t have arrived at independently. The company backed that up with three earlier patent filings from the US, China, and Japan, all describing similar bayonet mounts, terminals, and anti-misinsertion features.

Nikon fought back and even narrowed its claims during the process, but the panel wasn’t convinced. It found the differences between Nikon’s design and the prior art were either already suggested in those earlier filings, standard knowledge in the field, or just obvious engineering choices (four lugs instead of three being one example). The whole patent got tossed on that basis.

As CineD notes, an invalid patent can’t support an infringement claim, so knocking it out first is seen as Viltrox’s defensive move. However, the infringement case itself is still only reported through unverified sources – neither Nikon nor Viltrox has issued a public statement.

Nikon has three months to challenge the ruling before the Beijing Intellectual Property Court, and the decision applies only to this one patent in China. Nikon still holds plenty of other Z-system patents, and this ruling says nothing about autofocus operation or electronic communication protocols.

The Bigger Picture

Nothing’s slowed down on Viltrox’s end. The company kept releasing Z-mount glass throughout the proceedings, and its catalog now spans well beyond mirrorless primes.

CineD mentions Sony and Canon, and I find these examples interesting and important for understanding this case better. Sony publishes an official list of E-mount licensees, while Canon has licensed its RF mount to select Sigma lenses. Viltrox isn’t recognized as a licensee by either. Nikon, on the other hand, has never published a partner list or an open Z-mount spec at all. So Viltrox probably got to its Z-mount through reverse-engineering rather than an authorized deal – which is exactly what Nikon is now trying to resolve.

[via CineD]

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