Fujifilm GFX100RF:
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Patent JP-2025-178957 Details GFX100RF Lens and a Mysterious 28mm Formula
A newly published patent (JP-2025-178957, published Dec 9, 2025) has surfaced, giving us a fascinating look under the hood of the GFX100RF. While we have been enjoying the camera since April, this filing reveals exactly how Fujifilm’s engineers managed to fit a medium format lens into such a compact body.
However, the patent contains a second optical example that is raising eyebrows: a 28mm lens that does not appear to cover the medium format sensor at all.
The GFX100RF Lens: 35mm f/4 (Example 2)
The second example in the patent describes a 35mm f/4 lens with an image height of approximately 28.2mm. This perfectly matches the GFX sensor (which requires a roughly 27-28mm image height to cover the semi-diagonal).
This confirms the optical DNA of the GFX100RF. The design utilizes a back focus of just ~5.4mm, allowing the rear element to sit virtually on top of the sensor. This ultra-short distance is what makes the camera so thin compared to GFX interchangeable lens bodies, but it necessitates the fixed-lens design with a built-in leaf shutter.
The Mystery: 28mm f/4 (Example 1)
Here is where things get interesting. Example 1 in the filing details a 28mm f/4 lens.
Initially, one might assume this was a wide-angle concept for a “GFX100RF Wide.” However, looking closely at the data, the image height (Y) for this lens is significantly smaller than what is required for medium format.
The image circle in Example 1 appears closer to Full Frame (36x24mm) or potentially a very aggressive APS-C projection. If this lens were mounted on a GFX sensor, it would likely produce massive mechanical vignetting.
What is the 28mm for?
There are a few possibilities for this “mystery lens”:
- A Full Frame Experiment: While Fujifilm has historically avoided Full Frame, patenting a fixed-lens formula for this format suggests they are at least exploring the optics required for a competitor to the Leica Q or Sony RX1 series.
- APS-C Wide Angle: This could be a new wide-angle formula for a future premium X-series compact (an “X80” successor or similar).
- Incomplete Data: It is possible the 28mm example relies on even heavier digital stretching than the 35mm, though covering the jump from Full Frame to Medium Format purely via distortion correction would be an extreme engineering feat.
For now, the patent serves as confirmation of the brilliant engineering in the GFX100RF, while leaving us with a very interesting breadcrumb regarding Fujifilm’s R&D into other sensor formats.
via J-PlatPat
