Adapter guide
Pentax K lenses on Fuji X
Yes, this works. Pentax K has a 45.46mm flange distance and Fujifilm X-mount has 17.7mm, so a 27.76mm mechanical adapter with no glass fills the gap and infinity focus is preserved. Focus and aperture stay manual.
- Pentax K flange
- 45.46 mm
- Fuji X flange
- 17.7 mm
- Adapter thickness
- 27.76 mm
- Optical elements
- None required
Setting it up
Set Shoot Without Lens to On and enter the focal length under Mount Adaptor Setting so stabilised bodies and EXIF know the lens. Focus peaking and digital split image work with any adapted lens.
Automatic diaphragm. Pentax-A and later lenses add an A position on the ring that hands aperture control to the body; leave it off A on an adapter.
Pentax K lenses and their field of view on Fuji X
Effective focal length changes with sensor size. The lens itself does not change; the smaller sensor simply captures a narrower part of the image circle.
| Lens | Focal length | Aperture | Frames like (APS-C (1.5x)) | Years | Used value |
|---|---|---|---|---|---|
| Pentax SMC Pentax 50mm f/1.2 | 50mm | f/1.2 | 75mm | 1975-1990s | $300 to $800 |
| Pentax SMC Pentax-M 50mm f/1.4 | 50mm | f/1.4 | 75mm | 1977-1984 | $60 to $210 |
Frequently asked
Do Pentax K lenses work on Fuji X cameras?
Yes. A plain Pentax K to Fuji X adapter works with no optics. Pentax K has a 45.46mm register and Fujifilm X-mount has a 17.7mm register, so the adapter is a 27.76mm tube that puts the lens exactly where a Pentax K body would. Plain adapter ring. Because K keeps the 45.46mm M42 register, M42 lenses also mount on K bodies with a thin adapter and keep infinity.
Do Pentax K lenses focus to infinity on Fuji X?
Yes. Because the adapter restores the native 45.46mm register, infinity focus is preserved and the full focus scale on the lens stays accurate. Adapters machined slightly short let the lens focus past infinity by a small margin, which is harmless; adapters machined long stop short of infinity, so buy from a maker with tight tolerances.
What focal length does a Pentax K lens become on Fuji X?
On APS-C (1.5x) Fuji X bodies (X-T, X-H, X-Pro, X-E, X-S, and X-M series) a 50mm lens frames like a 75mm lens on full frame; the aperture and depth of field at a given distance do not change.
More on this mount: Pentax K mount reference