Fujifilm G mount vs X mount: what's the difference?
Fujifilm X is APS-C at 17.70 mm; G (GFX) is medium format at 26.70 mm. Why XF and GF lenses never cross over, and what adapts onto each system instead.
Fujifilm X mount is the company’s APS-C mirrorless system, with a 17.70 mm flange focal distance. Fujifilm G mount is its medium-format GFX system, with a 26.70 mm flange distance and a sensor about four times the area. The two are completely separate: an XF or XC lens does not fit a GFX body, a GF lens does not fit an X body, and Fujifilm makes no adapter between them.
Beyond the brand name, the two systems share very little that matters when buying lenses.
The two mounts side by side
| Fujifilm X | Fujifilm G (GFX) | |
|---|---|---|
| Format | APS-C | Medium format |
| Sensor size | 23.5 × 15.7 mm (X-T5) | 43.8 × 32.9 mm |
| Field-of-view crop vs full frame | about 1.5× | about 0.79× |
| Flange focal distance | 17.70 mm | 26.70 mm |
| Throat diameter | not published | not published |
| Introduced | 2012 | 2017 |
| Lens names | XF, XC | GF |
Flange figures are from this site’s mount data. The X sensor size is from Fujifilm’s X-T5 specification; the GFX sensor size is from Fujifilm’s GFX system literature. Fujifilm has not published a throat diameter for either mount in this site’s data, so none is given here.
The X mount arrived in 2012 with the X-Pro1. The G mount followed in 2017 with the GFX 50S.
What the sensor difference means
The GFX sensor is 43.8 × 32.9 mm, against roughly 36 × 24 mm for full frame and 23.5 × 15.7 mm for X. By area it is about 1.7 times full frame and nearly four times Fujifilm’s APS-C.
In practice, a lens of a given focal length shows a much wider view on GFX than on X. A 50 mm lens frames like roughly a 40 mm lens on full frame when used on GFX, and like roughly a 75 mm lens on X. That is why GF and XF lenses with similar-looking fields of view have very different focal lengths.
The larger sensor also needs a larger image circle. That is the real reason the lenses are so different in size and cost, and it matters as much as the mount when thinking about adapting.
Why XF lenses do not fit GFX
Two reasons, either of which would be enough.
Flange distance. An X lens is designed to sit 17.70 mm from the sensor. A GFX body’s mount is 26.70 mm from its sensor. To focus at infinity, an X lens would have to sit 9.00 mm inside the camera. An adapter can only add distance, never take it away. The flange focal distance explainer covers the principle.
Image circle. Even if the lens could be positioned correctly, an XF lens projects an image circle sized for a 23.5 × 15.7 mm sensor. On a 43.8 × 32.9 mm sensor that would leave a small bright circle surrounded by black.
Why GF lenses do not go on X bodies
Here the arithmetic works on paper. G’s 26.70 mm is 9.00 mm longer than X’s 17.70 mm, comfortably more than the roughly 2 mm this site uses as the minimum for a plain adapter.
It still does not happen in practice, for three reasons:
- Electronics. GF lenses are electronic: the camera drives both focus and aperture. A plain spacer would leave you with a lens you cannot focus or control. Fujifilm makes no GF-to-X adapter, and this site has no electronic one on record.
- Waste. You would be paying for, and carrying, an image circle almost four times larger than the X sensor can use.
- Better options. X already has a large native range from Fujifilm plus licensed third-party autofocus lenses from Sigma, Tamron and Viltrox.
The Fujifilm G hub marks GF lenses as impractical to adapt out for this reason.
Adapting other lenses onto X
At 17.70 mm, X has one of the shorter flange distances in this site’s data, so most SLR and rangefinder lenses fit with a plain adapter.
Leica M (27.80 mm) leaves 10.10 mm. Fujifilm makes its own M Mount Adapter, and unusually it has electronic contacts. They do not add autofocus. Instead, they let you set the lens’s focal length and apply image corrections in the camera. Plain third-party rings also work, because M lenses are fully mechanical.
Canon EF (44.00 mm) leaves 26.30 mm. Fringer’s EF-FX Pro II is the best-known electronic adapter. It supports in-camera aperture control and phase-detect autofocus on X bodies from X-Trans II onwards. Performance varies by lens, and Fringer publishes its own compatibility list.
Manual SLR lenses fit with plain rings: Nikon F with 28.80 mm to spare, Pentax K and M42 with 27.76 mm, and Canon FD with 24.30 mm. Because X is APS-C, these lenses show the central part of their image, with a field of view about 1.5 times narrower than on a 35 mm camera.
What does not adapt usefully onto X: Sony E and Canon EF-M (only 0.30 mm longer, which leaves no room), Nikon Z (shorter than X), and Micro Four Thirds (1.55 mm longer, below this site’s 2 mm threshold, and its lenses cover a smaller sensor than X’s anyway). Canon RF and L-Mount clear the threshold at 2.30 mm, but both are electronic mounts with no licensed adapter to X.
Adapting other lenses onto GFX
The longer 26.70 mm flange distance cuts the list down, and the larger sensor cuts it further.
Hasselblad H. Fujifilm’s own H Mount Adapter G takes selected Fujinon HC and Hasselblad H lenses. The camera controls the aperture and the lens’s leaf shutter, with flash sync up to 1/800 second, but focusing is manual. This is the one adapted route that suits the format.
35 mm SLR lenses. Canon EF (17.30 mm to spare), Nikon F (19.80 mm), Pentax K and M42 (18.76 mm) and Canon FD (15.30 mm) all fit physically. Whether they cover the sensor is a property of the individual lens: they were designed to cover 36 × 24 mm, so many will vignette on the full GFX frame. GFX bodies have crop modes, but using one means recording a smaller part of the sensor.
Leica M is the exception to this site’s rules. At 27.80 mm it is only 1.10 mm longer than G, below the 2 mm this site’s matrix uses as a minimum, yet plain M-to-GFX adapters are made by Metabones, Novoflex, Fotodiox, Kipon and TTArtisan. They are manual only. Coverage is the same lens-by-lens question as for SLR lenses, and many M lenses will vignette on the full frame.
Which should you buy into?
This site covers mounts rather than cameras, but the mount facts point one way:
- X is the more flexible system for lenses. It has native third-party autofocus, a long list of adaptable SLR and rangefinder glass, and smaller, cheaper lenses.
- G is the choice if you specifically want the medium-format sensor. Its lens choice is narrower, and adapted 35 mm glass is a compromise rather than a bonus.
There is no upgrade path that takes XF lenses to GFX. Moving between the systems means replacing lenses.
Where to go next
- Fujifilm X mount and Fujifilm G mount hubs, with full specifications.
- The Leica M mount hub for the rangefinder lenses that adapt onto both.
- The compatibility matrix to check any lens mount against either body.