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Adapter compatibility · Canon → Pentax / Ricoh

Canon FD to Pentax K adapter compatibility

Mounting a Canon FD lens on a Pentax K body — the feasibility verdict, AF / IS / aperture-control / infinity-focus outcome, image-circle relationship, official and reputable third-party adapter SKUs, and the caveats worth knowing before you buy.

Verdict at a glance

Speed booster
MFIS lens-onlyAp. wheel

Mount specs

Lens side

Canon FD

Flange distance
42 mm
Protocol
Mechanical only
Type
legacy-SLR

Body side

Pentax K

Flange distance
45.46 mm
Protocol
Pentax K (KAF/KAF2/KAF3/KAF4)
Type
DSLR

The Canon FDlens’s flange distance (42 mm) is 3.46 mm shorter than the Pentax K body’s (45.46 mm). A mechanical adapter can only add distance between the lens and the sensor, never remove it, so a plain spacer cannot hold a Canon FD lens close enough to reach infinity focus. The verdict above calls for a focal reducer (Speed Booster) — its corrective optics bridge the deficit and add roughly a stop of light.

Flange-distance schematic. Two rails share a sensor plane on the right. The Pentax K body register measures 45.46 millimetres; the Canon FD lens needs only 42 millimetres, which is 3.46 millimetres shorter. The orange region marks the deficit a mechanical spacer cannot remove; a focal reducer is required.Sensor planePentax K body · 45.46 mmCanon FD lens · 42 mm−3.46 mm short
The Pentax K body holds any lens 45.46 mm off the sensor, but the Canon FD lens reaches infinity at 42 mm — 3.46 mm closer than the body allows. A mechanical adapter only adds distance, so a focal reducer (Speed Booster) is required to recover infinity focus.

Adapter examples

  • Speed Booster / focal-reducer family

Caveats

  • Flange clearance is only -3.5 mm — a plain mechanical adapter cannot reach infinity focus; a focal reducer (Speed Booster) with optical glass is required.
  • Speed Boosters typically widen the effective focal length (~0.71×) and add ~1 stop of light, which can be desirable on crop bodies.

Common questions

Will Canon FD lenses autofocus on a Pentax K body through an adapter?
No — Canon FD → Pentax K adapters are mechanical only. Focus is fully manual; rely on the Pentax K body's focus peaking and magnify-to-focus aids to nail focus.
Does in-lens image stabilization (IS / VR / OS) still work through a Canon FD → Pentax K adapter?
Lens-side only — the Canon FD lens's IS / VR / OS unit operates, but it cannot synchronise with the Pentax K body's IBIS, so the dual-axis stabilisation native Pentax K lenses enjoy isn't available. Lens-side stabilisation still delivers most of the practical benefit.
What's the most-recommended Canon FD → Pentax K adapter?
No SKU in our curated catalogue covers Canon FD → Pentax K yet. Adapter examples photographers commonly use include the Speed Booster / focal-reducer family. Pair compatibility is mostly mechanical, so any well-built adapter at the correct flange distance should work — pick on build quality and tripod-foot integration.

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